fix(debug): hardware watchpoints, signal stops and breakpoint restore

Assisted-by: GLM 5.3

cmd/gasm/debug_linux.go

@@ -53,7 +53,7 @@ REPL commands:
 	bufSpec := fs.String("buf", "", "buffer specification: name:size:pattern[,name:size:pattern...] where pattern is zero, ones, seq, or hex")
 	script := fs.String("script", "", "run REPL commands from a file (one per line) and exit; '-' reads stdin")
 	cover := fs.Bool("cover", false, "run to completion with a breakpoint on every instruction and report which executed and how often")
-	timeout := fs.Duration("timeout", 0, "kill the debuggee after this duration (e.g. 30s); for headless --script runs")
+	timeout := fs.Duration("timeout", 0, "kill the debuggee after this duration (e.g. 30s); for headless --script runs; a timeout exits 3")
 	fs.Parse(args)
 
 	// --- Debuggee mode (internal, spawned by the debugger) ---
@@ -231,6 +231,13 @@ REPL commands:
 			if sess.Exited() {
 				break
 			}
+			// A genuine signal-delivery-stop (a fault in the kernel): the
+			// run cannot make progress, because resuming would restart the
+			// faulting instruction and fault forever.  Report and stop.
+			if sig := sess.LastSignal(); sig != 0 {
+				fmt.Printf("gasm debug: cover: stopped on signal %v\n", sig)
+				break
+			}
 			regs, rerr := sess.GetRegs()
 			if rerr != nil {
 				break

debug/breakpoint.go

@@ -9,11 +9,11 @@ import "strings"
 
 import "fmt"
 
-// Breakpoint is one INT3 breakpoint in the debuggee.
+// Breakpoint is one software breakpoint in the debuggee.
 type Breakpoint struct {
 	Addr    uint64 // absolute address in the debuggee
 	Label   string // source label ("" for raw addresses)
-	Orig    byte   // original byte at Addr (restored on removal)
+	Orig    []byte // original bytes at Addr (restored on removal)
 	Enabled bool
 	Cond    *Condition // optional condition (nil = unconditional)
 	hits    int
@@ -32,8 +32,12 @@ type Condition struct {
 	MemAddr uint64 // memory address (for register-memory comparison, prefixed with *)
 }
 
-// Eval checks the condition against the current registers.
+// Eval checks the condition against the current registers.  For the
-func (c *Condition) Eval(regs *Regs) bool {
+// register-memory form, mem reads an 8-byte little-endian word from the
+// debuggee; it may be nil when no reader is available.  Anything that cannot
+// be decided (unknown register or operator, unreadable memory) does not
+// block the breakpoint.
+func (c *Condition) Eval(regs *Regs, mem func(addr uint64) (uint64, bool)) bool {
 	actual, ok := regs.RegValue(c.Reg)
 	if !ok {
 		return true // unknown register, don't block
@@ -48,9 +52,16 @@ func (c *Condition) Eval(regs *Regs) bool {
 		}
 		expected = v
 	case c.MemAddr != 0:
-		// Register-memory comparison, requires a Session, not available here.
+		// Register-memory comparison, resolved in the debuggee at
-		// Fall back to treating as constant (the caller should resolve).
+		// evaluation time.
-		expected = c.Value
+		if mem == nil {
+			return true
+		}
+		v, ok := mem(c.MemAddr)
+		if !ok {
+			return true
+		}
+		expected = v
 	default:
 		expected = c.Value
 	}
@@ -72,6 +83,18 @@ func (c *Condition) Eval(regs *Regs) bool {
 	}
 }
 
+// String renders the condition for display.
+func (c *Condition) String() string {
+	switch {
+	case c.Reg2 != "":
+		return fmt.Sprintf("%s %s %s", c.Reg, c.Op, c.Reg2)
+	case c.MemAddr != 0:
+		return fmt.Sprintf("%s %s *%#x", c.Reg, c.Op, c.MemAddr)
+	default:
+		return fmt.Sprintf("%s %s %#x", c.Reg, c.Op, c.Value)
+	}
+}
+
 // Breakpoints manages the software breakpoints of one Session.
 type Breakpoints struct {
 	t   tracer
@@ -83,6 +106,18 @@ func NewBreakpoints(t tracer) *Breakpoints {
 	return &Breakpoints{t: t, bps: make(map[uint64]*Breakpoint)}
 }
 
+// breakpointMask is the byte mask of the breakpoint instruction inside a
+// peeked word: the low len(breakpointInsn) bytes, because every supported
+// architecture is little-endian and patches the instruction at the lowest
+// address of the word.
+func breakpointMask() uint64 {
+	var mask uint64
+	for range breakpointInsn {
+		mask = (mask << 8) | 0xFF
+	}
+	return mask
+}
+
 // Set installs a breakpoint at addr (replaces any existing one).
 func (bm *Breakpoints) Set(addr uint64, label string) (*Breakpoint, error) {
 	return bm.SetWithCond(addr, label, nil)
@@ -100,13 +135,12 @@ func (bm *Breakpoints) SetWithCond(addr uint64, label string, cond *Condition) (
 	if err != nil {
 		return nil, err
 	}
-	orig := byte(word)
+	orig := make([]byte, len(breakpointInsn))
-	// Patch with the breakpoint instruction, preserving the rest of the word.
+	for i := range orig {
-	mask := uint64(0)
+		orig[i] = byte(word >> (8 * i))
-	for range breakpointInsn {
-		mask = (mask << 8) | 0xFF
 	}
-	patched := (word &^ mask) | breakpointWord(breakpointInsn)
+	// Patch with the breakpoint instruction, preserving the rest of the word.
+	patched := (word &^ breakpointMask()) | breakpointWord(breakpointInsn)
 	if err := bm.t.Poke(addr, patched); err != nil {
 		return nil, err
 	}
@@ -134,26 +168,40 @@ func (bm *Breakpoints) Info() string {
 		}
 		cond := ""
 		if bp.Cond != nil {
-			cond = fmt.Sprintf(" if %s %s %#x", bp.Cond.Reg, bp.Cond.Op, bp.Cond.Value)
+			cond = " if " + bp.Cond.String()
 		}
 		result.WriteString(fmt.Sprintf("  %d: %s at %#x [%s, %d hits]%s\n", i, label, bp.Addr, status, bp.hits, cond))
 	}
 	return result.String()
 }
 
-// Clear removes the breakpoint at addr, restoring the original byte.
+// restore writes the saved original bytes back over the breakpoint
+// instruction, preserving the rest of the peeked word.  It reports whether
+// both the peek and the poke succeeded.
+func (bm *Breakpoints) restore(addr uint64, bp *Breakpoint) bool {
+	word, err := bm.t.Peek(addr)
+	if err != nil {
+		return false
+	}
+	orig := uint64(0)
+	for i, b := range bp.Orig {
+		orig |= uint64(b) << (8 * i)
+	}
+	return bm.t.Poke(addr, (word&^breakpointMask())|orig) == nil
+}
+
+// Clear removes the breakpoint at addr, restoring the original bytes.
 func (bm *Breakpoints) Clear(addr uint64) error {
 	bp, ok := bm.bps[addr]
 	if !ok {
 		return fmt.Errorf("debug: no breakpoint at %#x", addr)
 	}
-	word, err := bm.t.Peek(addr)
+	if !bm.restore(addr, bp) {
-	if err != nil {
+		word, err := bm.t.Peek(addr)
-		return err
+		if err != nil {
-	}
+			return err
-	restored := (word &^ 0xFF) | uint64(bp.Orig)
+		}
-	if err := bm.t.Poke(addr, restored); err != nil {
+		return fmt.Errorf("debug: restore breakpoint at %#x failed, word is %#x", addr, word)
-		return err
 	}
 	delete(bm.bps, addr)
 	return nil
@@ -185,43 +233,54 @@ func (bm *Breakpoints) All() []*Breakpoint {
 
 // HandleTrap is called after the debuggee stops on SIGTRAP.  It checks
 // whether the trap was caused by one of our breakpoints (PC-adjust matches
-// a breakpoint address), restores the original byte, rewinds PC, and
+// a breakpoint address), restores the original bytes, rewinds PC, and
 // returns the breakpoint that was hit (or nil if it was a single-step).
 // Hits returns how many times the breakpoint has been hit.
 func (bp *Breakpoint) Hits() int { return bp.hits }
 
 func (bm *Breakpoints) HandleTrap(regs *Regs) *Breakpoint {
-	// After a breakpoint trap, PC points past the breakpoint instruction.
+	// On amd64 the kernel reports the trap with RIP past the INT3; on the
+	// other supported architectures the PC still stands on the trap
+	// instruction, which breakpointPCAdjust encodes per architecture.
 	trapAddr := regs.GetPC() - uint64(breakpointPCAdjust)
 	bp, ok := bm.bps[trapAddr]
 	if !ok || !bp.Enabled {
 		return nil // single-step trap or unknown
 	}
 	// Check the condition (if any).
-	if bp.Cond != nil && !bp.Cond.Eval(regs) {
+	if bp.Cond != nil && !bp.Cond.Eval(regs, bm.peekValue) {
-		// Condition not met, restore the byte but do NOT rewind RIP.
+		// Condition not met: step the original instruction and re-arm the
-		// The process continues from the next instruction (past the INT3).
+		// breakpoint, leaving the debuggee stopped just past it, ready to
-		word, err := bm.t.Peek(trapAddr)
+		// resume silently.  The PC must be rewound first: on architectures
-		if err == nil {
+		// that report the trap past the instruction (amd64) it would
-			restored := (word &^ 0xFF) | uint64(bp.Orig)
+		// otherwise sit on the second byte of the replaced instruction.
-			bm.t.Poke(trapAddr, restored)
+		if !bm.restore(trapAddr, bp) {
+			return nil
 		}
-		// RIP is already past the INT3 (trapAddr + 1). Don't rewind.
+		regs.SetPC(trapAddr)
+		if err := bm.t.SetRegs(regs); err != nil {
+			return nil
+		}
+		if err := bm.t.Step(); err != nil {
+			return nil
+		}
+		bm.Reinsert(trapAddr)
 		return nil
 	}
 	bp.hits++
-	// Restore the original byte.
+	// Restore the original bytes and rewind PC to re-execute them.
-	word, err := bm.t.Peek(trapAddr)
+	bm.restore(trapAddr, bp)
-	if err == nil {
-		restored := (word &^ 0xFF) | uint64(bp.Orig)
-		bm.t.Poke(trapAddr, restored)
-	}
-	// Rewind PC to re-execute the original instruction.
 	regs.SetPC(trapAddr)
 	bm.t.SetRegs(regs)
 	return bp
 }
 
+// peekValue adapts tracer.Peek to the Condition value reader.
+func (bm *Breakpoints) peekValue(addr uint64) (uint64, bool) {
+	v, err := bm.t.Peek(addr)
+	return v, err == nil
+}
+
 // Reinsert re-inserts the breakpoint at addr after a single-step past it.
 // Called after Step() when we want the breakpoint to fire again on the
 // next Continue().
@@ -234,11 +293,7 @@ func (bm *Breakpoints) Reinsert(addr uint64) error {
 	if err != nil {
 		return err
 	}
-	mask := uint64(0)
+	patched := (word &^ breakpointMask()) | breakpointWord(breakpointInsn)
-	for range breakpointInsn {
-		mask = (mask << 8) | 0xFF
-	}
-	patched := (word &^ mask) | breakpointWord(breakpointInsn)
 	return bm.t.Poke(addr, patched)
 }
 

debug/debug_arch_test.go

@@ -0,0 +1,265 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build linux
+
+package debug
+
+// Architecture-neutral tests: label and line tables, and the breakpoint
+// manager against the mock tracer.  These do not launch a debuggee, so they
+// build on every supported linux architecture.
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestLineAt(t *testing.T) {
+	lines := []SourceLine{
+		{Offset: 0, Line: 5},
+		{Offset: 5, Line: 6},
+		{Offset: 10, Line: 7},
+		{Offset: 15, Line: 8},
+	}
+
+	tests := []struct {
+		offset int
+		want   int
+	}{
+		{0, 5},
+		{1, 5},
+		{4, 5},
+		{5, 6},
+		{7, 6},
+		{10, 7},
+		{12, 7},
+		{15, 8},
+		{20, 8},
+	}
+
+	for _, tt := range tests {
+		got := lineAt(lines, tt.offset)
+		if got != tt.want {
+			t.Errorf("lineAt(lines, %d) = %d, want %d", tt.offset, got, tt.want)
+		}
+	}
+
+	// Empty table.
+	if lineAt(nil, 5) != 0 {
+		t.Error("lineAt(nil, 5) should return 0")
+	}
+}
+
+func TestOffsetForLine(t *testing.T) {
+	lines := []SourceLine{
+		{Offset: 0, Line: 5},
+		{Offset: 5, Line: 6},
+		{Offset: 10, Line: 7},
+	}
+
+	tests := []struct {
+		line int
+		want int
+	}{
+		{5, 0},
+		{6, 5},
+		{7, 10},
+		{99, -1}, // not found
+		{0, -1},  // not found
+	}
+
+	for _, tt := range tests {
+		got := offsetForLine(lines, tt.line)
+		if got != tt.want {
+			t.Errorf("offsetForLine(lines, %d) = %d, want %d", tt.line, got, tt.want)
+		}
+	}
+}
+
+func TestNearestLabel(t *testing.T) {
+	labels := []Label{
+		{Name: "start", Offset: 0},
+		{Name: "loop", Offset: 10},
+		{Name: "done", Offset: 20},
+	}
+
+	tests := []struct {
+		offset int
+		want   string
+	}{
+		{0, "start"},
+		{5, "start"},
+		{10, "loop"},
+		{15, "loop"},
+		{20, "done"},
+		{25, "done"},
+	}
+
+	for _, tt := range tests {
+		got := nearestLabel(labels, tt.offset)
+		if got != tt.want {
+			t.Errorf("nearestLabel(labels, %d) = %q, want %q", tt.offset, got, tt.want)
+		}
+	}
+}
+
+func TestBreakpointsSetAndClear(t *testing.T) {
+	tr := newMockTracer()
+	bm := NewBreakpoints(tr)
+
+	// Set a breakpoint at address 0x1000.
+	bp, err := bm.Set(0x1000, "test")
+	if err != nil {
+		t.Fatalf("Set: %v", err)
+	}
+	if !bp.Enabled {
+		t.Error("breakpoint not enabled")
+	}
+	if bp.Label != "test" {
+		t.Errorf("label = %q, want test", bp.Label)
+	}
+
+	// Verify Peek was called.
+	if len(tr.peeks) != 1 || tr.peeks[0] != 0x1000 {
+		t.Errorf("peeks = %v, want [0x1000]", tr.peeks)
+	}
+
+	// Verify Poke wrote the breakpoint instruction's bytes.
+	if len(tr.pokes) != 1 || tr.pokes[0].addr != 0x1000 {
+		t.Errorf("pokes = %v", tr.pokes)
+	}
+	if got := tr.pokes[0].val & breakpointMask(); got != breakpointWord(breakpointInsn) {
+		t.Errorf("patched bytes %#x, want %#x", got, breakpointWord(breakpointInsn))
+	}
+
+	// At should find it.
+	if bm.At(0x1000) == nil {
+		t.Error("At(0x1000) returned nil")
+	}
+
+	// All should return it.
+	all := bm.All()
+	if len(all) != 1 {
+		t.Errorf("All() = %d breakpoints, want 1", len(all))
+	}
+
+	// Clear it.
+	if err := bm.Clear(0x1000); err != nil {
+		t.Fatalf("Clear: %v", err)
+	}
+	if bm.At(0x1000) != nil {
+		t.Error("At(0x1000) after Clear should be nil")
+	}
+}
+
+// TestBreakpointRestoreWidth proves the restore path writes back every
+// byte of the breakpoint instruction's width, not just the first byte: on
+// arm64, riscv64 and loong64 the instruction is four bytes, and restoring
+// one byte would leave three bytes of the trap instruction in place.
+func TestBreakpointRestoreWidth(t *testing.T) {
+	tr := newMockTracer()
+	bm := NewBreakpoints(tr)
+	tr.mem[0x3000] = 0x11
+	tr.mem[0x3001] = 0x22
+	tr.mem[0x3002] = 0x33
+	tr.mem[0x3003] = 0x44
+
+	if _, err := bm.Set(0x3000, "width"); err != nil {
+		t.Fatalf("Set: %v", err)
+	}
+	for i, b := range breakpointInsn {
+		if tr.mem[0x3000+uint64(i)] != b {
+			t.Fatalf("byte %d after Set = %#x, want the breakpoint byte %#x", i, tr.mem[0x3000+uint64(i)], b)
+		}
+	}
+	if len(bm.At(0x3000).Orig) != len(breakpointInsn) {
+		t.Fatalf("Orig holds %d bytes, want %d", len(bm.At(0x3000).Orig), len(breakpointInsn))
+	}
+
+	if err := bm.Clear(0x3000); err != nil {
+		t.Fatalf("Clear: %v", err)
+	}
+	want := []byte{0x11, 0x22, 0x33, 0x44}
+	for i, b := range want {
+		if tr.mem[0x3000+uint64(i)] != b {
+			t.Errorf("byte %d after Clear = %#x, want %#x (restore must cover the full instruction width)", i, tr.mem[0x3000+uint64(i)], b)
+		}
+	}
+}
+
+func TestBreakpointsSetWithCond(t *testing.T) {
+	tr := newMockTracer()
+	bm := NewBreakpoints(tr)
+
+	cond := &Condition{Reg: "rax", Op: "==", Value: 42}
+	bp, err := bm.SetWithCond(0x2000, "cond_test", cond)
+	if err != nil {
+		t.Fatalf("SetWithCond: %v", err)
+	}
+	if bp.Cond == nil || bp.Cond.Value != 42 {
+		t.Error("condition not set")
+	}
+
+	// Re-setting the same address should update the condition.
+	cond2 := &Condition{Reg: "rbx", Op: "<", Value: 100}
+	bp2, err := bm.SetWithCond(0x2000, "cond_test2", cond2)
+	if err != nil {
+		t.Fatalf("SetWithCond (update): %v", err)
+	}
+	if bp2.Cond.Value != 100 {
+		t.Error("condition not updated")
+	}
+	// Should have only 1 Peek (first Set), second is update (no Peek needed).
+	if len(tr.peeks) != 1 {
+		t.Errorf("expected 1 Peek, got %d", len(tr.peeks))
+	}
+}
+
+func TestBreakpointsClearAll(t *testing.T) {
+	tr := newMockTracer()
+	bm := NewBreakpoints(tr)
+
+	bm.Set(0x1000, "a")
+	bm.Set(0x2000, "b")
+	bm.Set(0x3000, "c")
+
+	if len(bm.All()) != 3 {
+		t.Fatalf("expected 3 breakpoints, got %d", len(bm.All()))
+	}
+
+	bm.ClearAll()
+	if len(bm.All()) != 0 {
+		t.Errorf("ClearAll: expected 0 breakpoints, got %d", len(bm.All()))
+	}
+}
+
+func TestBreakpointInfo(t *testing.T) {
+	tr := newMockTracer()
+	bm := NewBreakpoints(tr)
+	bm.Set(0x4000, "info_test")
+
+	info := bm.Info()
+	if info == "" {
+		t.Error("Info returned empty string")
+	}
+	if !strings.Contains(info, "info_test") {
+		t.Errorf("Info %q does not contain label", info)
+	}
+}
+
+// TestConditionString covers the display of all three condition forms.
+func TestConditionString(t *testing.T) {
+	tests := []struct {
+		cond Condition
+		want string
+	}{
+		{Condition{Reg: "rax", Op: "==", Value: 42}, "rax == 0x2a"},
+		{Condition{Reg: "rax", Op: "!=", Reg2: "rbx"}, "rax != rbx"},
+		{Condition{Reg: "rax", Op: "<", MemAddr: 0x5000}, "rax < *0x5000"},
+	}
+	for _, tt := range tests {
+		if got := tt.cond.String(); got != tt.want {
+			t.Errorf("Condition.String() = %q, want %q", got, tt.want)
+		}
+	}
+}

debug/debug_test.go

@@ -6,7 +6,6 @@
 package debug
 
 import (
-	"strings"
 	"testing"
 )
 
@@ -48,7 +47,7 @@ func TestConditionEval(t *testing.T) {
 	}
 
 	for _, tt := range tests {
-		got := tt.cond.Eval(regs)
+		got := tt.cond.Eval(regs, nil)
 		if got != tt.want {
 			t.Errorf("Condition{%q %q %d}.Eval() = %v, want %v",
 				tt.cond.Reg, tt.cond.Op, tt.cond.Value, got, tt.want)
@@ -56,65 +55,33 @@ func TestConditionEval(t *testing.T) {
 	}
 }
 
-func TestLineAt(t *testing.T) {
+// TestConditionEvalMem covers the register-memory form: the value is read
-	lines := []SourceLine{
+// through the supplied reader, and a missing or failing reader must not
-		{Offset: 0, Line: 5},
+// block the breakpoint.
-		{Offset: 5, Line: 6},
+func TestConditionEvalMem(t *testing.T) {
-		{Offset: 10, Line: 7},
+	regs := &Regs{RAX: 7}
-		{Offset: 15, Line: 8},
+	mem := func(addr uint64) (uint64, bool) {
-	}
+		if addr == 0x5000 {
-
+			return 7, true
-	tests := []struct {
-		offset int
-		want   int
-	}{
-		{0, 5},
-		{1, 5},
-		{4, 5},
-		{5, 6},
-		{7, 6},
-		{10, 7},
-		{12, 7},
-		{15, 8},
-		{20, 8},
-	}
-
-	for _, tt := range tests {
-		got := lineAt(lines, tt.offset)
-		if got != tt.want {
-			t.Errorf("lineAt(lines, %d) = %d, want %d", tt.offset, got, tt.want)
 		}
+		return 0, false
 	}
 
-	// Empty table.
+	eq := Condition{Reg: "rax", Op: "==", MemAddr: 0x5000}
-	if lineAt(nil, 5) != 0 {
+	if !eq.Eval(regs, mem) {
-		t.Error("lineAt(nil, 5) should return 0")
+		t.Error("register-memory comparison with matching word should hold")
 	}
-}
+	ne := Condition{Reg: "rax", Op: "!=", MemAddr: 0x5000}
-
+	if ne.Eval(regs, mem) {
-func TestOffsetForLine(t *testing.T) {
+		t.Error("register-memory comparison with mismatching word should not hold")
-	lines := []SourceLine{
-		{Offset: 0, Line: 5},
-		{Offset: 5, Line: 6},
-		{Offset: 10, Line: 7},
 	}
-
+	bad := Condition{Reg: "rax", Op: "==", MemAddr: 0x6000}
-	tests := []struct {
+	if !bad.Eval(regs, mem) {
-		line int
+		t.Error("unreadable memory must not block the breakpoint")
-		want int
-	}{
-		{5, 0},
-		{6, 5},
-		{7, 10},
-		{99, -1}, // not found
-		{0, -1},  // not found
 	}
-
+	noReader := Condition{Reg: "rax", Op: "==", MemAddr: 0x5000}
-	for _, tt := range tests {
+	if !noReader.Eval(regs, nil) {
-		got := offsetForLine(lines, tt.line)
+		t.Error("missing memory reader must not block the breakpoint")
-		if got != tt.want {
-			t.Errorf("offsetForLine(lines, %d) = %d, want %d", tt.line, got, tt.want)
-		}
 	}
 }
 
@@ -141,139 +108,6 @@ func TestDecodeRflags(t *testing.T) {
 	}
 }
 
-func TestNearestLabel(t *testing.T) {
-	labels := []Label{
-		{Name: "start", Offset: 0},
-		{Name: "loop", Offset: 10},
-		{Name: "done", Offset: 20},
-	}
-
-	tests := []struct {
-		offset int
-		want   string
-	}{
-		{0, "start"},
-		{5, "start"},
-		{10, "loop"},
-		{15, "loop"},
-		{20, "done"},
-		{25, "done"},
-	}
-
-	for _, tt := range tests {
-		got := nearestLabel(labels, tt.offset)
-		if got != tt.want {
-			t.Errorf("nearestLabel(labels, %d) = %q, want %q", tt.offset, got, tt.want)
-		}
-	}
-}
-
-func TestBreakpointsSetAndClear(t *testing.T) {
-	tr := newMockTracer()
-	bm := NewBreakpoints(tr)
-
-	// Set a breakpoint at address 0x1000.
-	bp, err := bm.Set(0x1000, "test")
-	if err != nil {
-		t.Fatalf("Set: %v", err)
-	}
-	if !bp.Enabled {
-		t.Error("breakpoint not enabled")
-	}
-	if bp.Label != "test" {
-		t.Errorf("label = %q, want test", bp.Label)
-	}
-
-	// Verify Peek was called.
-	if len(tr.peeks) != 1 || tr.peeks[0] != 0x1000 {
-		t.Errorf("peeks = %v, want [0x1000]", tr.peeks)
-	}
-
-	// Verify Poke wrote INT3.
-	if len(tr.pokes) != 1 || tr.pokes[0].addr != 0x1000 {
-		t.Errorf("pokes = %v", tr.pokes)
-	}
-
-	// At should find it.
-	if bm.At(0x1000) == nil {
-		t.Error("At(0x1000) returned nil")
-	}
-
-	// All should return it.
-	all := bm.All()
-	if len(all) != 1 {
-		t.Errorf("All() = %d breakpoints, want 1", len(all))
-	}
-
-	// Clear it.
-	if err := bm.Clear(0x1000); err != nil {
-		t.Fatalf("Clear: %v", err)
-	}
-	if bm.At(0x1000) != nil {
-		t.Error("At(0x1000) after Clear should be nil")
-	}
-}
-
-func TestBreakpointsSetWithCond(t *testing.T) {
-	tr := newMockTracer()
-	bm := NewBreakpoints(tr)
-
-	cond := &Condition{Reg: "rax", Op: "==", Value: 42}
-	bp, err := bm.SetWithCond(0x2000, "cond_test", cond)
-	if err != nil {
-		t.Fatalf("SetWithCond: %v", err)
-	}
-	if bp.Cond == nil || bp.Cond.Value != 42 {
-		t.Error("condition not set")
-	}
-
-	// Re-setting the same address should update the condition.
-	cond2 := &Condition{Reg: "rbx", Op: "<", Value: 100}
-	bp2, err := bm.SetWithCond(0x2000, "cond_test2", cond2)
-	if err != nil {
-		t.Fatalf("SetWithCond (update): %v", err)
-	}
-	if bp2.Cond.Value != 100 {
-		t.Error("condition not updated")
-	}
-	// Should have only 1 Peek (first Set), second is update (no Peek needed).
-	if len(tr.peeks) != 1 {
-		t.Errorf("expected 1 Peek, got %d", len(tr.peeks))
-	}
-}
-
-func TestBreakpointsClearAll(t *testing.T) {
-	tr := newMockTracer()
-	bm := NewBreakpoints(tr)
-
-	bm.Set(0x1000, "a")
-	bm.Set(0x2000, "b")
-	bm.Set(0x3000, "c")
-
-	if len(bm.All()) != 3 {
-		t.Fatalf("expected 3 breakpoints, got %d", len(bm.All()))
-	}
-
-	bm.ClearAll()
-	if len(bm.All()) != 0 {
-		t.Errorf("ClearAll: expected 0 breakpoints, got %d", len(bm.All()))
-	}
-}
-
-func TestBreakpointInfo(t *testing.T) {
-	tr := newMockTracer()
-	bm := NewBreakpoints(tr)
-	bm.Set(0x4000, "info_test")
-
-	info := bm.Info()
-	if info == "" {
-		t.Error("Info returned empty string")
-	}
-	if !strings.Contains(info, "info_test") {
-		t.Errorf("Info %q does not contain label", info)
-	}
-}
-
 func TestWatchpointSlotTracking(t *testing.T) {
 	s := &Session{} // per-session slots start free
 
@@ -323,3 +157,19 @@ func TestWatchpointSlotTracking(t *testing.T) {
 		t.Errorf("FindFreeWatchpointSlot() with all slots used = %d, want -1", got)
 	}
 }
+
+// TestUnwatchSlotBound checks the bound the REPL parses against: it must
+// cover the architecture's whole slot range, not a hardcoded 0-3.
+func TestUnwatchSlotBound(t *testing.T) {
+	max := maxWatchpoints()
+	if max < 4 {
+		t.Fatalf("maxWatchpoints() = %d, want at least 4", max)
+	}
+	s := &Session{}
+	if s.IsWatchpointSlotUsed(max - 1) {
+		t.Errorf("slot %d should be free initially", max-1)
+	}
+	if s.IsWatchpointSlotUsed(max) {
+		t.Errorf("slot %d must be out of range", max)
+	}
+}

debug/disasm_linux_amd64.go

@@ -46,3 +46,11 @@ func (s *Session) DisassembleN(addr uint64, n int) string {
 	}
 	return result.String()
 }
+
+// isCallInsn reports whether disassembled text (x86asm.IntelSyntax) is a
+// call.  The first token must match exactly: a prefix test would also catch
+// unrelated mnemonics.
+func isCallInsn(text string) bool {
+	m, _, _ := strings.Cut(text, " ")
+	return strings.ToLower(m) == "call"
+}

debug/disasm_linux_arm64.go

@@ -7,6 +7,7 @@ package debug
 
 import (
 	"fmt"
+	"strings"
 
 	"sourcedock.dev/petrbalvin/gasm-devkit/arch"
 	"sourcedock.dev/petrbalvin/gasm-devkit/disasm"
@@ -44,3 +45,15 @@ func (s *Session) DisassembleN(addr uint64, n int) string {
 	}
 	return result
 }
+
+// isCallInsn reports whether disassembled text (arm64asm.GoSyntax) is a
+// call.  GoSyntax renders bl as CALL; the native mnemonic is accepted too.
+// The first token must match exactly so branches never match.
+func isCallInsn(text string) bool {
+	m, _, _ := strings.Cut(text, " ")
+	switch strings.ToLower(m) {
+	case "call", "bl":
+		return true
+	}
+	return false
+}

debug/disasm_linux_loong64.go

@@ -7,6 +7,7 @@ package debug
 
 import (
 	"fmt"
+	"strings"
 
 	"sourcedock.dev/petrbalvin/gasm-devkit/arch"
 	"sourcedock.dev/petrbalvin/gasm-devkit/disasm"
@@ -44,3 +45,16 @@ func (s *Session) DisassembleN(addr uint64, n int) string {
 	}
 	return result
 }
+
+// isCallInsn reports whether disassembled text (loong64asm.GoSyntax) is a
+// call.  GoSyntax renders bl and jirl calls as CALL (jirl returns print
+// RET); the native mnemonics are accepted too.  The first token must match
+// exactly: a "bl" prefix would catch bltz and other branches.
+func isCallInsn(text string) bool {
+	m, _, _ := strings.Cut(text, " ")
+	switch strings.ToLower(m) {
+	case "call", "bl", "jirl":
+		return true
+	}
+	return false
+}

debug/disasm_linux_riscv64.go

@@ -7,6 +7,7 @@ package debug
 
 import (
 	"fmt"
+	"strings"
 
 	"sourcedock.dev/petrbalvin/gasm-devkit/arch"
 	"sourcedock.dev/petrbalvin/gasm-devkit/disasm"
@@ -44,3 +45,17 @@ func (s *Session) DisassembleN(addr uint64, n int) string {
 	}
 	return result
 }
+
+// isCallInsn reports whether disassembled text (riscv64asm.GoSyntax) is a
+// call.  GoSyntax renders jal and jalr calls as CALL; the native mnemonics
+// are accepted too.  The first token must match exactly: a prefix test on
+// "bl" would catch branches on other architectures, and jalr as ret prints
+// RET, which must not be stepped over.
+func isCallInsn(text string) bool {
+	m, _, _ := strings.Cut(text, " ")
+	switch strings.ToLower(m) {
+	case "call", "jal", "jalr":
+		return true
+	}
+	return false
+}

debug/display_linux_amd64.go

@@ -73,9 +73,29 @@ func decodeRflags(f uint64) string {
 	return flags[:len(flags)-1]
 }
 
-// archReturnAddr reads the return address from the stack (amd64 ABI0 convention).
+// archReturnAddr reads the return address of the current frame (amd64
+// ABI0 convention).  A function that contains a CALL (or has a frame) is
+// assembled with the prologue PUSHQ BP; MOVQ SP, BP, so mid-function the
+// word at SP is the saved caller BP, a stack address, and the return
+// address sits further up.  Walk the stack from SP and take the first word
+// that lies in an executable mapping: stack and data words never do, a
+// return address always does.
 func archReturnAddr(s *Session, regs *Regs) (uint64, error) {
-	return s.Peek(regs.GetSP())
+	ranges := execRanges(s.pid)
+	for off := uint64(0); off < 512; off += 8 {
+		word, err := s.Peek(regs.RSP + off)
+		if err != nil {
+			break
+		}
+		for _, r := range ranges {
+			if word >= r.lo && word < r.hi {
+				return word, nil
+			}
+		}
+	}
+	// No mapping available or nothing code-like on the stack: fall back to
+	// the raw entry convention, [SP] before any push.
+	return s.Peek(regs.RSP)
 }
 
 // archSPLabel returns the SP register name for display.

debug/display_linux_arm64.go

@@ -5,7 +5,10 @@
 
 package debug
 
-import "fmt"
+import (
+	"encoding/binary"
+	"fmt"
+)
 
 func printRegs(regs *Regs, codeBase, funcOff uint64) {
 	fmt.Printf("  PC  = %#016x  (func+%#x)\n", regs.PC, regs.PC-codeBase-funcOff)
@@ -31,8 +34,8 @@ func printRegs(regs *Regs, codeBase, funcOff uint64) {
 func printVectorRegs(v *VectorRegs) {
 	fmt.Println("\n  Vector registers (V0-V31):")
 	for i := 0; i < 32; i += 2 {
-		fmt.Printf("  V%-2d  = %016x%016x\n", i, v.V[i][8], v.V[i][0])
+		fmt.Printf("  V%-2d  = %016x%016x\n", i, binary.LittleEndian.Uint64(v.V[i][8:16]), binary.LittleEndian.Uint64(v.V[i][0:8]))
-		fmt.Printf("  V%-2d  = %016x%016x\n", i+1, v.V[i+1][8], v.V[i+1][0])
+		fmt.Printf("  V%-2d  = %016x%016x\n", i+1, binary.LittleEndian.Uint64(v.V[i+1][8:16]), binary.LittleEndian.Uint64(v.V[i+1][0:8]))
 	}
 }
 

debug/ptrace_extra_test.go

@@ -0,0 +1,427 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build linux && amd64
+
+package debug
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+	"time"
+	"unsafe"
+
+	"sourcedock.dev/petrbalvin/gasm-devkit/asm"
+	"sourcedock.dev/petrbalvin/gasm-devkit/verify"
+)
+
+// Integration tests beyond the basic entry breakpoint: hardware watchpoints,
+// conditional breakpoints, next/finish over a CALL, faulting kernels and the
+// xstate vector-register readout.  All drive a real ptrace session, so they
+// run on amd64 hosts only.
+
+// writeKernel writes an assembly source to a temporary file with the
+// architecture suffix the assembler dispatcher expects.
+func writeKernel(t *testing.T, src string) string {
+	t.Helper()
+	path := filepath.Join(t.TempDir(), "kernel_amd64.s")
+	if err := os.WriteFile(path, []byte(src), 0o644); err != nil {
+		t.Fatalf("write kernel: %v", err)
+	}
+	return path
+}
+
+// launchKernel launches a session for the kernel source and returns the
+// session, its breakpoint manager and the function layout.
+func launchKernel(t *testing.T, bin, path, funcName string, args []byte) (*Session, *Breakpoints, asm.FuncLayout) {
+	t.Helper()
+	k, err := verify.Load(path)
+	if err != nil {
+		t.Fatalf("Load: %v", err)
+	}
+	t.Cleanup(k.Close)
+	fl, err := k.Func(funcName)
+	if err != nil {
+		t.Fatalf("Func: %v", err)
+	}
+	if len(args) < fl.Args {
+		padded := make([]byte, fl.Args)
+		copy(padded, args)
+		args = padded
+	}
+	sess, err := Launch(bin, path, funcName, args)
+	if err != nil {
+		t.Fatalf("Launch: %v", err)
+	}
+	t.Cleanup(sess.Kill)
+	bm := NewBreakpoints(sess)
+	return sess, bm, fl
+}
+
+// runToEntry resumes the freshly launched debuggee until the breakpoint at
+// the function entry traps, mirroring the REPL continue loop: the debuggee
+// SIGSTOPs twice (launch barrier and entry barrier) before entering the JIT
+// call.
+func runToEntry(t *testing.T, sess *Session, bm *Breakpoints, entry uint64) {
+	t.Helper()
+	for range 50 {
+		for _, bp := range bm.All() {
+			bm.Reinsert(bp.Addr)
+		}
+		if err := sess.Continue(); err != nil {
+			t.Fatalf("Continue: %v", err)
+		}
+		if sess.Exited() {
+			t.Fatal("debuggee exited before the entry breakpoint trapped")
+		}
+		regs, err := sess.GetRegs()
+		if err != nil {
+			t.Fatalf("GetRegs: %v", err)
+		}
+		if bm.HandleTrap(&regs) != nil {
+			return
+		}
+	}
+	t.Fatal("no entry breakpoint trap after 50 resumes")
+}
+
+// captureStdout runs fn with os.Stdout redirected to a pipe and returns
+// what it printed (the REPL writes its reports to stdout).
+func captureStdout(t *testing.T, fn func()) string {
+	t.Helper()
+	r, w, err := os.Pipe()
+	if err != nil {
+		t.Fatalf("pipe: %v", err)
+	}
+	old := os.Stdout
+	os.Stdout = w
+	done := make(chan string, 1)
+	go func() {
+		b, _ := io.ReadAll(r)
+		done <- string(b)
+	}()
+	defer func() { os.Stdout = old }()
+	fn()
+	w.Close()
+	return <-done
+}
+
+// TestWatchpointArmRunHit proves the debug-register offsets: the watchpoint
+// must fire on the store, with si_addr naming the watched address.  The
+// kernel writes its return value to ret+0(FP), which is the 8-byte word
+// right above the stack pointer at entry.
+func TestWatchpointArmRunHit(t *testing.T) {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+	bin := buildGasm(t)
+
+	const kernel = `#include "textflag.h"
+
+// func wpret() int64
+TEXT ·wpret(SB), NOSPLIT, $0-8
+	MOVQ $0x5a5a5a5a5a5a5a5a, AX
+	MOVQ AX, ret+0(FP)
+	RET
+`
+	path := writeKernel(t, kernel)
+	sess, bm, fl := launchKernel(t, bin, path, "wpret", nil)
+
+	entry := sess.CodeBase() + uint64(fl.Offset)
+	if _, err := bm.Set(entry, "entry"); err != nil {
+		t.Fatalf("Set: %v", err)
+	}
+	runToEntry(t, sess, bm, entry)
+
+	regs, err := sess.GetRegs()
+	if err != nil {
+		t.Fatalf("GetRegs: %v", err)
+	}
+	watched := regs.RSP + 8 // ret+0(FP): the store target
+
+	slot := sess.FindFreeWatchpointSlot()
+	if slot < 0 {
+		t.Fatal("no free watchpoint slot")
+	}
+	if err := sess.SetWatchpoint(slot, watched, WatchWrite, 8); err != nil {
+		t.Fatalf("SetWatchpoint: %v (wrong debug-register offsets?)", err)
+	}
+
+	if err := sess.Continue(); err != nil {
+		t.Fatalf("Continue: %v", err)
+	}
+	reason, addr := sess.StopInfo()
+	if reason != StopWatchpoint {
+		t.Fatalf("stop reason = %v, want StopWatchpoint (DR0-DR3/DR7 offsets are wrong)", reason)
+	}
+	if addr != watched {
+		t.Fatalf("watchpoint address = %#x, want %#x", addr, watched)
+	}
+
+	// The watched word holds the stored value: x86 data breakpoints are
+	// reported with the access complete.
+	if word, err := sess.Peek(watched); err != nil || word != 0x5a5a5a5a5a5a5a5a {
+		t.Errorf("watched word = %#x (err %v), want 0x5a5a5a5a5a5a5a5a", word, err)
+	}
+	if err := sess.ClearWatchpoint(slot); err != nil {
+		t.Fatalf("ClearWatchpoint: %v", err)
+	}
+}
+
+// TestConditionalBreakpointFalseThenTrue proves the false-condition path:
+// the breakpoint steps over the original instruction, re-arms itself and
+// keeps running silently, and the true condition stops exactly once with the
+// register in the expected state.
+func TestConditionalBreakpointFalseThenTrue(t *testing.T) {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+	bin := buildGasm(t)
+
+	const kernel = `#include "textflag.h"
+
+// func countdown(n int64) int64
+TEXT ·countdown(SB), NOSPLIT, $0-16
+	MOVQ n+0(FP), CX
+loop:
+	DECQ CX
+	CMPQ CX, $0
+	JNE loop
+	MOVQ CX, ret+8(FP)
+	RET
+`
+	path := writeKernel(t, kernel)
+	sess, bm, fl := launchKernel(t, bin, path, "countdown", []byte{8})
+
+	loopAddr := sess.CodeBase() + uint64(fl.Offset) + uint64(fl.Labels["loop"])
+	// The length of the breakpointed instruction, from a disassembly taken
+	// before the INT3 is patched in.
+	_, insnLen, err := sess.Disassemble(loopAddr)
+	if err != nil || insnLen <= 0 {
+		t.Fatalf("Disassemble at %#x: len=%d err=%v", loopAddr, insnLen, err)
+	}
+	cond := &Condition{Reg: "rcx", Op: "==", Value: 1}
+	bp, err := bm.SetWithCond(loopAddr, "loop", cond)
+	if err != nil {
+		t.Fatalf("SetWithCond: %v", err)
+	}
+
+	hits := 0
+	exited := false
+	for range 200 {
+		for _, b := range bm.All() {
+			bm.Reinsert(b.Addr)
+		}
+		if err := sess.Continue(); err != nil {
+			exited = true
+			break // the debuggee finished
+		}
+		if sess.Exited() {
+			exited = true
+			break
+		}
+		if sig := sess.LastSignal(); sig != 0 {
+			t.Fatalf("unexpected signal stop %v", sig)
+		}
+		regs, err := sess.GetRegs()
+		if err != nil {
+			t.Fatalf("GetRegs: %v", err)
+		}
+		if hit := bm.HandleTrap(&regs); hit != nil {
+			hits++
+			if regs.RCX != 1 {
+				t.Fatalf("hit with RCX=%d, want 1", regs.RCX)
+			}
+			// Park after the instruction, as the REPL does.
+			if err := sess.Step(); err != nil {
+				t.Fatalf("Step: %v", err)
+			}
+		} else {
+			// A false evaluation must leave the debuggee past the whole
+			// original instruction: a PC inside it (trapAddr+1 on amd64)
+			// means the resume happens mid-instruction.
+			fresh, err := sess.GetRegs()
+			if err != nil {
+				t.Fatalf("GetRegs: %v", err)
+			}
+			if fresh.RIP > loopAddr && fresh.RIP < loopAddr+uint64(insnLen) {
+				t.Fatalf("false evaluation left the PC at %#x, inside the %d-byte instruction at %#x",
+					fresh.RIP, insnLen, loopAddr)
+			}
+		}
+	}
+	if hits != 1 {
+		t.Fatalf("conditional breakpoint hit %d times, want exactly 1 (false evaluations must run through silently)", hits)
+	}
+	if bp.Hits() != 1 {
+		t.Errorf("bp.Hits() = %d, want 1", bp.Hits())
+	}
+	if !exited || !sess.Exited() {
+		t.Fatal("debuggee did not run to completion after the conditional hit")
+	}
+}
+
+// TestNextAndFinishOverCall proves next and finish evaluate the trap with
+// registers fetched after the stop: next lands exactly on the instruction
+// after the CALL, and finish stops exactly on the return address.
+func TestNextAndFinishOverCall(t *testing.T) {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+	bin := buildGasm(t)
+
+	const kernel = `#include "textflag.h"
+
+// func caller(x int64) int64
+// The argument travels in AX: FP argument slots of CALL-bearing functions
+// are an assembler concern outside this test's scope.
+TEXT ·caller(SB), NOSPLIT, $0-16
+	MOVQ $5, AX
+	CALL ·bump(SB)
+aftercall:
+	MOVQ AX, ret+8(FP)
+	RET
+
+// func bump(x int64) int64
+TEXT ·bump(SB), NOSPLIT, $0-0
+	ADDQ $3, AX
+	RET
+`
+	path := writeKernel(t, kernel)
+
+	// next: step the prologue and the constant load (3 instructions), then
+	// step over the CALL and check the landing address and RAX.
+	sess, bm, fl := launchKernel(t, bin, path, "caller", nil)
+	entry := sess.CodeBase() + uint64(fl.Offset)
+	if _, err := bm.Set(entry, "entry"); err != nil {
+		t.Fatalf("Set: %v", err)
+	}
+	runToEntry(t, sess, bm, entry)
+	afterOff := uint64(fl.Labels["aftercall"])
+
+	out := captureStdout(t, func() {
+		REPL(sess, bm, sess.CodeBase(), fl.Offset, fl.Size, fl.Args, nil, nil,
+			strings.NewReader("step 3\nnext\nregs\nquit\n"))
+	})
+	if !strings.Contains(out, fmt.Sprintf("func+%#x", afterOff)) {
+		t.Errorf("next did not land on the instruction after the CALL (func+%#x); output:\n%s", afterOff, out)
+	}
+	if !strings.Contains(out, "RAX = 0x0000000000000008") {
+		t.Errorf("callee did not run exactly once under next (want RAX=8); output:\n%s", out)
+	}
+
+	// finish: run to the return address read off the stack at entry.
+	sess2, bm2, fl2 := launchKernel(t, bin, path, "caller", nil)
+	entry2 := sess2.CodeBase() + uint64(fl2.Offset)
+	if _, err := bm2.Set(entry2, "entry"); err != nil {
+		t.Fatalf("Set: %v", err)
+	}
+	runToEntry(t, sess2, bm2, entry2)
+	regs, err := sess2.GetRegs()
+	if err != nil {
+		t.Fatalf("GetRegs: %v", err)
+	}
+	retAddr, err := sess2.Peek(regs.RSP)
+	if err != nil {
+		t.Fatalf("Peek return address: %v", err)
+	}
+
+	out2 := captureStdout(t, func() {
+		REPL(sess2, bm2, sess2.CodeBase(), fl2.Offset, fl2.Size, fl2.Args, nil, nil,
+			strings.NewReader("step 1\nfinish\nquit\n"))
+	})
+	want := fmt.Sprintf("finished, now at %#x\n", retAddr)
+	if !strings.Contains(out2, want) {
+		t.Errorf("finish stopped at the wrong PC; want %q in output:\n%s", want, out2)
+	}
+}
+
+// TestSignalStopSurfaced proves a faulting kernel surfaces as a reported
+// stop instead of an infinite fault loop.  A regression here hangs, so a
+// watchdog fails the run rather than letting CI stall.
+func TestSignalStopSurfaced(t *testing.T) {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+	bin := buildGasm(t)
+
+	const kernel = `#include "textflag.h"
+
+// func crash() int64
+TEXT ·crash(SB), NOSPLIT, $0-8
+	XORQ AX, AX
+	MOVQ (AX), AX
+	MOVQ AX, ret+0(FP)
+	RET
+`
+	path := writeKernel(t, kernel)
+	sess, bm, _ := launchKernel(t, bin, path, "crash", nil)
+
+	timer := time.AfterFunc(time.Minute, func() {
+		panic("watchdog: the debugger hung on the faulting kernel instead of reporting the signal stop")
+	})
+	defer timer.Stop()
+
+	out := captureStdout(t, func() {
+		REPL(sess, bm, sess.CodeBase(), 0, 0, 0, nil, nil,
+			strings.NewReader("continue\nquit\n"))
+	})
+	if !strings.Contains(out, "stopped on signal") {
+		t.Errorf("SIGSEGV did not surface as a reported stop; output:\n%s", out)
+	}
+	if !sess.Exited() {
+		t.Error("debuggee should be killed by quit after the signal stop")
+	}
+}
+
+// TestGetVectorRegsXState proves the NT_X86_XSTATE readout: the request
+// succeeds on a normal process and the XMM halves agree with
+// PTRACE_GETFPREGS.
+func TestGetVectorRegsXState(t *testing.T) {
+	// The FPRegs layout must mirror the kernel's user_fpregs_struct
+	// exactly: PTRACE_GETFPREGS fills all 512 bytes, so a short struct
+	// overflows the caller's memory.
+	if got := unsafe.Sizeof(FPRegs{}); got != 512 {
+		t.Fatalf("sizeof(FPRegs) = %d, want 512", got)
+	}
+	if got := unsafe.Offsetof(FPRegs{}.XMM); got != 160 {
+		t.Fatalf("offsetof(FPRegs.XMM) = %d, want 160", got)
+	}
+
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+	bin := buildGasm(t)
+
+	const kernel = `#include "textflag.h"
+
+// func vprobe() int64
+TEXT ·vprobe(SB), NOSPLIT, $0-8
+	MOVQ $1, AX
+	MOVQ AX, ret+0(FP)
+	RET
+`
+	path := writeKernel(t, kernel)
+	sess, bm, fl := launchKernel(t, bin, path, "vprobe", nil)
+
+	entry := sess.CodeBase() + uint64(fl.Offset)
+	if _, err := bm.Set(entry, "entry"); err != nil {
+		t.Fatalf("Set: %v", err)
+	}
+	runToEntry(t, sess, bm, entry)
+
+	v, err := sess.GetVectorRegs()
+	if err != nil {
+		t.Fatalf("GetVectorRegs: %v", err)
+	}
+	fp, err := sess.GetFPRegs()
+	if err != nil {
+		t.Fatalf("GetFPRegs: %v", err)
+	}
+	for i := range 16 {
+		if !bytes.Equal(v.YMM[i][:16], fp.XMM[i][:]) {
+			t.Errorf("YMM%d low half %x, want the FPRegs XMM half %x", i, v.YMM[i][:16], fp.XMM[i][:])
+		}
+	}
+}

debug/ptrace_linux.go

@@ -23,7 +23,13 @@ type Session struct {
 	stopped  bool
 	exited   bool
 	codeBase uint64   // base address of the JIT code in the debuggee
-	wpSlots  [16]bool // hardware watchpoint slots in use (DR0-DR3, arm64 BADVR0-15)
+	tmpDir   string   // scratch directory of the session, removed on Kill
+	wpSlots  [16]bool // hardware watchpoint slots in use (DR0-DR3, arm64 DBGWVR0-15)
+	// lastSignal holds the signal of the most recent stop when that stop
+	// was a genuine signal-delivery-stop the caller must see (a fault such
+	// as SIGSEGV, SIGBUS, SIGFPE or SIGILL); 0 for breakpoint traps,
+	// single-steps, SIGSTOP and suppressed runtime signals.
+	lastSignal syscall.Signal
 }
 
 // Launch starts the debuggee subprocess (gasm debug --target ...) and
@@ -78,7 +84,7 @@ func LaunchWithBuffers(gasmBin, asmPath, funcName string, args []byte, bufSpec s
 		return nil, nil, fmt.Errorf("debug: start debuggee: %w", err)
 	}
 
-	s := &Session{pid: cmd.Process.Pid, cmd: cmd}
+	s := &Session{pid: cmd.Process.Pid, cmd: cmd, tmpDir: tmpDir}
 
 	readyFile := filepath.Join(tmpDir, "ready")
 	for range 500 {
@@ -125,29 +131,17 @@ func LaunchWithBuffers(gasmBin, asmPath, funcName string, args []byte, bufSpec s
 	return s, bufAddrs, nil
 }
 
-// wait waits for the debuggee to stop and returns the wait status.
-func (s *Session) wait() error {
-	var ws syscall.WaitStatus
-	_, err := syscall.Wait4(s.pid, &ws, 0, nil)
-	if err != nil {
-		return err
-	}
-	if ws.Exited() {
-		s.exited = true
-		return fmt.Errorf("debuggee exited with status %d", ws.ExitStatus())
-	}
-	s.stopped = true
-	return nil
-}
-
 // waitStopped consumes ptrace-stop events until one the debugger cares
-// about arrives: SIGTRAP (a breakpoint or a completed single-step) or the
+// about arrives: SIGTRAP (a breakpoint or a completed single-step), the
-// debuggee's own SIGSTOP.  A Go tracee's runtime raises SIGURG for
+// debuggee's own SIGSTOP, or a genuine signal-delivery-stop.  A Go tracee's
-// asynchronous preemption, and every signal on a traced thread surfaces as
+// runtime raises SIGURG for asynchronous preemption, and every signal on a
-// a signal-delivery-stop, so those are suppressed and the tracee resumed
+// traced thread surfaces as a signal-delivery-stop, so SIGURG is suppressed
-// without them.  Runtime noise is why a single wait can return in the
+// and the tracee resumed without it.  Every other signal (SIGSEGV, SIGBUS,
-// middle of runtime code and a resume can then fail: the event stream must
+// SIGFPE, SIGILL, ...) is returned to the caller: resuming with signal 0
-// be drained by the tracer.
+// would restart the faulting instruction and fault forever, so a faulting
+// kernel must surface as a stop the caller reports.  Runtime noise is also
+// why a single wait can return in the middle of runtime code and a resume
+// can then fail: the event stream must be drained by the tracer.
 func (s *Session) waitStopped() (syscall.Signal, error) {
 	for {
 		var ws syscall.WaitStatus
@@ -165,10 +159,12 @@ func (s *Session) waitStopped() (syscall.Signal, error) {
 		switch sig := ws.StopSignal(); sig {
 		case syscall.SIGTRAP, syscall.SIGSTOP:
 			s.stopped = true
+			s.lastSignal = 0
 			return sig, nil
-		default:
+		case syscall.SIGURG:
-			// Runtime noise (SIGURG preemption and friends): resume the
+			// Go runtime asynchronous preemption: resume the tracee
-			// tracee without delivering the signal.
+			// without delivering the signal.
+			s.lastSignal = 0
 			if _, _, errno := syscall.Syscall6(
 				syscall.SYS_PTRACE,
 				uintptr(syscall.PTRACE_CONT),
@@ -177,10 +173,22 @@ func (s *Session) waitStopped() (syscall.Signal, error) {
 			); errno != 0 {
 				return 0, fmt.Errorf("debug: PTRACE_CONT: %w", errno)
 			}
+		default:
+			// A genuine signal-delivery-stop.  Report it; the caller
+			// decides how to proceed.
+			s.stopped = true
+			s.lastSignal = sig
+			return sig, nil
 		}
 	}
 }
 
+// LastSignal returns the signal of the most recent stop when that stop was
+// a genuine signal-delivery-stop (a fault such as SIGSEGV, SIGFPE, SIGILL
+// or SIGBUS), and 0 for breakpoint traps, single-steps, SIGSTOP and
+// suppressed runtime signals.
+func (s *Session) LastSignal() syscall.Signal { return s.lastSignal }
+
 // Peek reads a word (8 bytes) from the debuggee's memory at addr.
 func (s *Session) Peek(addr uint64) (uint64, error) {
 	mem, err := os.OpenFile(fmt.Sprintf("/proc/%d/mem", s.pid), os.O_RDONLY, 0)
@@ -294,7 +302,8 @@ func (s *Session) Pid() int { return s.pid }
 // CodeBase returns the base address of the JIT code in the debuggee.
 func (s *Session) CodeBase() uint64 { return s.codeBase }
 
-// Kill terminates the debuggee.
+// Kill terminates the debuggee and removes the session's scratch
+// directory, so a successful session leaves no gasm-debug-* debris behind.
 func (s *Session) Kill() {
 	if !s.exited {
 		syscall.Kill(s.pid, syscall.SIGKILL)
@@ -304,6 +313,35 @@ func (s *Session) Kill() {
 	if s.cmd != nil && s.cmd.Process != nil {
 		s.cmd.Wait()
 	}
+	if s.tmpDir != "" {
+		os.RemoveAll(s.tmpDir)
+		s.tmpDir = ""
+	}
+}
+
+// execRange is one executable mapping of the debuggee.
+type execRange struct {
+	lo, hi uint64
+}
+
+// execRanges parses the debuggee's executable mappings from /proc/pid/maps.
+func execRanges(pid int) []execRange {
+	data, err := os.ReadFile(fmt.Sprintf("/proc/%d/maps", pid))
+	if err != nil {
+		return nil
+	}
+	var out []execRange
+	for line := range strings.SplitSeq(string(data), "\n") {
+		fields := strings.Fields(line)
+		if len(fields) < 2 || !strings.Contains(fields[1], "x") {
+			continue
+		}
+		var lo, hi uint64
+		if _, err := fmt.Sscanf(fields[0], "%x-%x", &lo, &hi); err == nil {
+			out = append(out, execRange{lo, hi})
+		}
+	}
+	return out
 }
 
 // findRWXMapping reads /proc/pid/maps and returns the base address of the

debug/ptrace_linux_amd64.go

@@ -6,6 +6,7 @@
 package debug
 
 import (
+	"encoding/binary"
 	"fmt"
 	"syscall"
 	"unsafe"
@@ -44,20 +45,24 @@ func (s *Session) SetRegs(regs *Regs) error {
 	return nil
 }
 
-// FPRegs holds the x87 FPU and SSE (XMM) register state from PTRACE_GETFPREGS.
+// FPRegs holds the x87 FPU and SSE (XMM) register state from
+// PTRACE_GETFPREGS.  The layout is the kernel's struct user_fpregs_struct
+// (sys/user.h), the FXSAVE image: 512 bytes with XMM0-15 at offset 160.
+// The i387 fcs/ds segment fields do not exist in the 64-bit layout.  The
+// size matters: the copy fills all 512 bytes, so a short or misaligned
+// struct makes PTRACE_GETFPREGS overflow the caller's memory.
 type FPRegs struct {
 	FCW       uint16
 	FSW       uint16
-	FTW       byte
+	FTW       uint16
 	FOP       uint16
 	FIP       uint64
-	FCS       uint16
 	FDP       uint64
-	FDS       uint16
 	MXCSR     uint32
 	MXCSRMask uint32
 	ST        [8][16]byte  // x87 stack (10 bytes per reg, padded to 16)
-	XMM       [16][16]byte // XMM0-15
+	XMM       [16][16]byte // XMM0-15, struct offset 160
+	Reserved  [96]byte     // FXSAVE padding, to the full 512 bytes
 }
 
 // GetFPRegs retrieves the FPU/SSE register state of the stopped debuggee.
@@ -82,16 +87,68 @@ type VectorRegs struct {
 	YMM [16][32]byte // YMM0-15 (full 256-bit values)
 }
 
-// GetVectorRegs retrieves the YMM registers via PTRACE_GETREGSET + XSAVE.
+// NT_X86_XSTATE (0x202), the xsave extended-state regset
+// (include/uapi/linux/elf.h).
+const ntX86XState = 0x202
+
+// Layout of the buffer PTRACE_GETREGSET returns for NT_X86_XSTATE: the
+// 512-byte legacy fxsave image (x87 state in 0-159, XMM0-15 in 160-511),
+// then the 64-byte xsave header whose first 8 bytes are xstate_bv, then one
+// component per set feature bit, each 64-byte aligned.  The YMM high halves
+// are the first extended component, at offset 576; that offset is fixed by
+// the ISA on AVX-capable x86-64.  XFEATURE_MASK_YMM is bit 2 of xstate_bv
+// (arch/x86/include/asm/fpu/types.h); the high halves are zero when the bit
+// is clear.
+const (
+	xsaveXMMOffset    = 160
+	xsaveXMMSize      = 256
+	xsaveHeaderOffset = 512
+	xsaveBVOffset     = xsaveHeaderOffset
+	ymmOffset         = xsaveHeaderOffset + 64 // 576
+	ymmSize           = 256                    // 16 registers, 16 bytes each
+	xfeatureMaskYMM   = 1 << 2
+	xstateMaxBuffer   = 4096 // CPUID(0xD).xsave_size is far below this
+)
+
+// GetVectorRegs retrieves the YMM registers via PTRACE_GETREGSET on
+// NT_X86_XSTATE.  The low (XMM) halves always come from the legacy image;
+// the high halves are copied only when xstate_bv reports the YMM feature,
+// and read as zero otherwise.  When the regset request fails the FP image
+// still provides correct XMM halves, so that is the fallback.
 func (s *Session) GetVectorRegs() (VectorRegs, error) {
 	var v VectorRegs
-	fp, err := s.GetFPRegs()
+	buf := make([]byte, xstateMaxBuffer)
-	if err != nil {
+	iovec := syscall.Iovec{
-		return v, err
+		Base: &buf[0],
+		Len:  uint64(len(buf)),
 	}
+	_, _, errno := syscall.Syscall6(
+		syscall.SYS_PTRACE,
+		uintptr(syscall.PTRACE_GETREGSET),
+		uintptr(s.pid),
+		uintptr(ntX86XState),
+		uintptr(unsafe.Pointer(&iovec)),
+		0, 0,
+	)
+	if errno != 0 {
+		fp, err := s.GetFPRegs()
+		if err != nil {
+			return v, err
+		}
+		for i := range 16 {
+			copy(v.YMM[i][:16], fp.XMM[i][:])
+		}
+		return v, nil
+	}
+	n := int(iovec.Len)
 	for i := range 16 {
-		for j := range 16 {
+		copy(v.YMM[i][:16], buf[xsaveXMMOffset+16*i:xsaveXMMOffset+16*i+16])
-			v.YMM[i][j] = fp.XMM[i][j]
+	}
+	if n >= ymmOffset+ymmSize {
+		if binary.LittleEndian.Uint64(buf[xsaveBVOffset:xsaveBVOffset+8])&xfeatureMaskYMM != 0 {
+			for i := range 16 {
+				copy(v.YMM[i][16:], buf[ymmOffset+16*i:ymmOffset+16*i+16])
+			}
 		}
 	}
 	return v, nil

debug/regs_linux_amd64.go

@@ -91,5 +91,9 @@ func (r *Regs) RegValue(name string) (uint64, bool) {
 // breakpointInsn is the software breakpoint instruction.
 var breakpointInsn = []byte{0xCC} // INT3
 
-// breakpointPCAdjust is how far PC is past the breakpoint instruction after a trap.
+// breakpointPCAdjust is how far PC is past the breakpoint instruction after
+// a trap.  x86-64 reports the #DB for INT3 with RIP on the byte after the
+// INT3 (Intel SDM vol 3, "Debug Exceptions"), so the trap address is
+// PC-1.  The other supported architectures leave the PC on the trap
+// instruction and use 0 there.
 const breakpointPCAdjust = 1

debug/regs_linux_arm64.go

@@ -130,5 +130,11 @@ func (r *Regs) RegValue(name string) (uint64, bool) {
 // breakpointInsn is the software breakpoint instruction (BRK #0).
 var breakpointInsn = []byte{0x00, 0x00, 0x20, 0xD4} // BRK #0
 
-// breakpointPCAdjust is how far PC is past the breakpoint instruction after a trap.
+// breakpointPCAdjust is how far PC is past the breakpoint instruction after
-const breakpointPCAdjust = 4
+// a trap: 0, because the arm64 kernel delivers the BRK SIGTRAP with the PC
+// still on the BRK.  do_el0_brk64 calls send_user_sigtrap, which uses
+// instruction_pointer(regs) unmodified (arch/arm64/kernel/debug-monitors.c);
+// only the kernel-internal skip paths advance the PC.  GDB history agrees:
+// decr_pc_after_break on aarch64 Linux is 0 (the +4 variant was a QEMU bug,
+// sourceware PR 17280).
+const breakpointPCAdjust = 0

debug/regs_linux_loong64.go

@@ -126,5 +126,9 @@ func (r *Regs) RegValue(name string) (uint64, bool) {
 // breakpointInsn is the software breakpoint instruction (BRK $0).
 var breakpointInsn = []byte{0x05, 0x00, 0x2a, 0x00} // break 0
 
-// breakpointPCAdjust is how far PC is past the breakpoint instruction after a trap.
+// breakpointPCAdjust is how far PC is past the breakpoint instruction after
-const breakpointPCAdjust = 4
+// a trap: 0, because the kernel delivers the break SIGTRAP with csr_era
+// still on the break instruction.  do_bp passes regs->csr_era straight to
+// force_sig_fault(SIGTRAP, TRAP_BRKPT, ...) and never adjusts era on the
+// signal path (arch/loongarch/kernel/traps.c).
+const breakpointPCAdjust = 0

debug/regs_linux_riscv64.go

@@ -126,5 +126,9 @@ func (r *Regs) RegValue(name string) (uint64, bool) {
 // breakpointInsn is the software breakpoint instruction (EBREAK).
 var breakpointInsn = []byte{0x73, 0x00, 0x10, 0x00} // ebreak
 
-// breakpointPCAdjust is how far PC is past the breakpoint instruction after a trap.
+// breakpointPCAdjust is how far PC is past the breakpoint instruction after
-const breakpointPCAdjust = 4
+// a trap: 0, because the kernel delivers the EBREAK SIGTRAP with sepc still
+// on the ebreak.  handle_break passes regs->epc straight to
+// force_sig_fault(SIGTRAP, TRAP_BRKPT, ...) and only the kernel-internal
+// WARN/CFI paths advance epc (arch/riscv/kernel/traps.c).
+const breakpointPCAdjust = 0

debug/repl.go

@@ -7,9 +7,10 @@ package debug
 
 import (
 	"bufio"
+	"cmp"
 	"fmt"
 	"io"
-	"sort"
+	"slices"
 	"strconv"
 	"strings"
 )
@@ -93,7 +94,7 @@ func REPL(s *Session, bm *Breakpoints, codeBase uint64, funcOffset, funcSize, ar
 			regs, _ := s.GetRegs()
 			pc := regs.GetPC()
 			text, instLen, _ := s.Disassemble(pc)
-			if strings.HasPrefix(strings.ToLower(text), "call") || strings.HasPrefix(strings.ToLower(text), "bl") {
+			if isCallInsn(text) {
 				afterAddr := pc + uint64(instLen)
 				_, err := bm.Set(afterAddr, "(next)")
 				if err != nil {
@@ -108,6 +109,21 @@ func REPL(s *Session, bm *Breakpoints, codeBase uint64, funcOffset, funcSize, ar
 					bm.Clear(afterAddr)
 					continue
 				}
+				if s.Exited() {
+					bm.Clear(afterAddr)
+					fmt.Println("debuggee exited")
+					continue
+				}
+				if sig := s.LastSignal(); sig != 0 {
+					bm.Clear(afterAddr)
+					regs, _ := s.GetRegs()
+					fmt.Printf("stopped on signal %v at %#x\n", sig, regs.GetPC())
+					continue
+				}
+				// Fetch the registers after the stop: the trap must be
+				// evaluated against the real PC, not the pre-Continue
+				// snapshot, and a stale SetRegs would clobber live state.
+				regs, _ = s.GetRegs()
 				bm.HandleTrap(&regs)
 				bm.Clear(afterAddr)
 			} else {
@@ -143,9 +159,21 @@ func REPL(s *Session, bm *Breakpoints, codeBase uint64, funcOffset, funcSize, ar
 				bm.Clear(retAddr)
 				continue
 			}
-			if !s.Exited() {
+			if s.Exited() {
-				bm.HandleTrap(&regs)
+				bm.Clear(retAddr)
+				fmt.Println("debuggee exited")
+				continue
 			}
+			if sig := s.LastSignal(); sig != 0 {
+				bm.Clear(retAddr)
+				regs, _ := s.GetRegs()
+				fmt.Printf("stopped on signal %v at %#x\n", sig, regs.GetPC())
+				continue
+			}
+			// Fetch the registers after the stop, as the continue case
+			// does: HandleTrap must see the PC the trap left behind.
+			regs, _ = s.GetRegs()
+			bm.HandleTrap(&regs)
 			bm.Clear(retAddr)
 			if s.Exited() {
 				fmt.Println("debuggee exited")
@@ -171,6 +199,15 @@ func REPL(s *Session, bm *Breakpoints, codeBase uint64, funcOffset, funcSize, ar
 					fmt.Println("debuggee exited")
 					break
 				}
+				if sig := s.LastSignal(); sig != 0 {
+					// A genuine signal-delivery-stop (a fault): report it
+					// and return to the prompt.  Continuing would restart
+					// the faulting instruction and fault forever.
+					regs, _ := s.GetRegs()
+					fmt.Printf("stopped on signal %v at %#x (func+%#x)\n",
+						sig, regs.GetPC(), regs.GetPC()-codeBase-uint64(funcOffset))
+					break
+				}
 				reason, wpAddr := s.StopInfo()
 				if reason == StopWatchpoint {
 					fmt.Printf("watchpoint hit at %#x\n", wpAddr)
@@ -221,13 +258,27 @@ func REPL(s *Session, bm *Breakpoints, codeBase uint64, funcOffset, funcSize, ar
 				reg := strings.ToLower(parts[3])
 				op := parts[4]
 				operand := parts[5]
-				if val, err := strconv.ParseUint(operand, 0, 64); err == nil {
+				switch {
-					cond = &Condition{Reg: reg, Op: op, Value: val}
+				case strings.HasPrefix(operand, "*"):
-				} else {
+					// Memory operand: compare against the 8-byte word at
-					cond = &Condition{Reg: reg, Op: op, Reg2: strings.ToLower(operand)}
+					// the address, resolved in the debuggee when the
+					// breakpoint is evaluated.
+					addr, err := strconv.ParseUint(strings.TrimPrefix(operand, "*"), 0, 64)
+					if err != nil {
+						fmt.Printf("invalid memory operand: %s\n", operand)
+						continue
+					}
+					cond = &Condition{Reg: reg, Op: op, MemAddr: addr}
+				default:
+					val, err := strconv.ParseUint(operand, 0, 64)
+					if err == nil {
+						cond = &Condition{Reg: reg, Op: op, Value: val}
+					} else {
+						cond = &Condition{Reg: reg, Op: op, Reg2: strings.ToLower(operand)}
+					}
 				}
 			} else if len(parts) >= 4 && parts[2] == "if" {
-				fmt.Println("usage: break <label|addr> if <reg> <op> <value|reg>")
+				fmt.Println("usage: break <label|addr> if <reg> <op> <value|reg|*addr>")
 				continue
 			}
 			bp, err := bm.SetWithCond(addr, label, cond)
@@ -237,7 +288,7 @@ func REPL(s *Session, bm *Breakpoints, codeBase uint64, funcOffset, funcSize, ar
 			}
 			condStr := ""
 			if cond != nil {
-				condStr = fmt.Sprintf(" if %s %s %#x", cond.Reg, cond.Op, cond.Value)
+				condStr = " if " + cond.String()
 			}
 			fmt.Printf("breakpoint set: %s at %#x (func+%#x)%s\n", bp.Label, bp.Addr, bp.Addr-codeBase-uint64(funcOffset), condStr)
 
@@ -277,7 +328,11 @@ func REPL(s *Session, bm *Breakpoints, codeBase uint64, funcOffset, funcSize, ar
 				addr, _ = resolveAddr(parts[1], codeBase, uint64(funcOffset), labels)
 			}
 			if len(parts) > 2 {
-				length, _ = strconv.Atoi(parts[2])
+				// A malformed or non-positive length would panic
+				// ReadMemory's make; fall back to the default instead.
+				if n, err := strconv.Atoi(parts[2]); err == nil && n > 0 {
+					length = n
+				}
 			}
 			mem, err := s.ReadMemory(addr, length)
 			if err != nil {
@@ -336,10 +391,8 @@ func REPL(s *Session, bm *Breakpoints, codeBase uint64, funcOffset, funcSize, ar
 			}
 
 		case "labels", "l":
-			sorted := make([]Label, len(labels))
+			slices.SortFunc(labels, func(a, b Label) int { return cmp.Compare(a.Offset, b.Offset) })
-			copy(sorted, labels)
+			for _, l := range labels {
-			sort.Slice(sorted, func(i, j int) bool { return sorted[i].Offset < sorted[j].Offset })
-			for _, l := range sorted {
 				fmt.Printf("  func+%#04x  %s\n", l.Offset, l.Name)
 			}
 
@@ -369,7 +422,10 @@ func REPL(s *Session, bm *Breakpoints, codeBase uint64, funcOffset, funcSize, ar
 			fmt.Println()
 
 		case "help", "h", "?":
-			fmt.Printf(`  break <label|addr> [if <reg> <op> <val>]  set a breakpoint
+			fmt.Printf(`  break <label|addr> [if <reg> <op> <val|reg|*addr>]
+                       set a breakpoint, optionally conditional on a
+                       register compared to a constant, a register, or the
+                       8-byte word at *addr
   delete <label|addr>  remove a breakpoint
   info break           list all breakpoints
   watch <addr> [r|w] [size]  set a hardware watchpoint (write by default)
@@ -463,8 +519,8 @@ func REPL(s *Session, bm *Breakpoints, codeBase uint64, funcOffset, funcSize, ar
 		case "unwatch":
 			if len(parts) >= 2 {
 				slot, err := strconv.Atoi(parts[1])
-				if err != nil || slot < 0 || slot > 3 {
+				if err != nil || slot < 0 || slot >= maxWatchpoints() {
-					fmt.Println("usage: unwatch [<slot>]")
+					fmt.Printf("usage: unwatch [<slot 0-%d>]\n", maxWatchpoints()-1)
 					continue
 				}
 				if err := s.ClearWatchpoint(slot); err != nil {

debug/stopinfo_linux.go

@@ -6,6 +6,7 @@
 package debug
 
 import (
+	"encoding/binary"
 	"syscall"
 	"unsafe"
 )
@@ -61,8 +62,15 @@ func (s *Session) StopInfo() (StopReason, uint64) {
 	case trapBRKPT:
 		return StopBreakpoint, 0
 	case trapHWBRKPT:
-		addr := *(*uint64)(unsafe.Add(unsafe.Pointer(&info), 16))
+		// si_addr sits at struct offset 16 (12 bytes of signo/errno/code
-		return StopWatchpoint, addr
+		// plus 4 bytes of union alignment).  The siginfo buffer is only
+		// 4-byte aligned, so the address is read byte-wise to keep the
+		// load aligned on riscv64 and loong64.  What si_addr names is
+		// architecture-specific (the data address on arm64, the
+		// instruction pointer on x86), so the per-architecture
+		// archWatchpointAddr resolves it to the watched address.
+		addr := binary.LittleEndian.Uint64(info._pad[4:12])
+		return StopWatchpoint, archWatchpointAddr(s, addr)
 	default:
 		return StopSingleStep, 0
 	}

debug/target_linux_arm64.go

@@ -28,15 +28,7 @@ func RunTarget(asmPath, funcName, argsFile, tmpDir string) error {
 		return fmt.Errorf("debug target: parse: %v", errs[0])
 	}
 
-	var img *asm.Image
+	img, err := asm.AssembleFileARM64(file)
-	switch "arm64" {
-	case "arm64":
-		img, err = asm.AssembleFileARM64(file)
-	case "riscv64":
-		img, err = asm.AssembleFileRISCV(file)
-	case "loong64":
-		img, err = asm.AssembleFileLOONG64(file)
-	}
 	if err != nil {
 		return fmt.Errorf("debug target: assemble: %w", err)
 	}

debug/target_linux_loong64.go

@@ -28,15 +28,7 @@ func RunTarget(asmPath, funcName, argsFile, tmpDir string) error {
 		return fmt.Errorf("debug target: parse: %v", errs[0])
 	}
 
-	var img *asm.Image
+	img, err := asm.AssembleFileLOONG64(file)
-	switch "loong64" {
-	case "arm64":
-		img, err = asm.AssembleFileARM64(file)
-	case "riscv64":
-		img, err = asm.AssembleFileRISCV(file)
-	case "loong64":
-		img, err = asm.AssembleFileLOONG64(file)
-	}
 	if err != nil {
 		return fmt.Errorf("debug target: assemble: %w", err)
 	}

debug/tracer.go

@@ -12,10 +12,11 @@ type tracer interface {
 	Peek(addr uint64) (uint64, error)
 	Poke(addr uint64, val uint64) error
 	SetRegs(regs *Regs) error
+	Step() error
 	Pid() int
 }
 
-// mockTracer records Peek/Poke calls and provides fake register state.
+// mockTracer records Peek/Poke/Step calls and provides fake register state.
 type mockTracer struct {
 	mem   map[uint64]byte
 	peeks []uint64
@@ -23,7 +24,8 @@ type mockTracer struct {
 		addr uint64
 		val  uint64
 	}
-	regs *Regs
+	steps int
+	regs  *Regs
 }
 
 func newMockTracer() *mockTracer {
@@ -57,4 +59,8 @@ func (m *mockTracer) SetRegs(regs *Regs) error {
 	m.regs = regs
 	return nil
 }
+func (m *mockTracer) Step() error {
+	m.steps++
+	return nil
+}
 func (m *mockTracer) Pid() int { return 42 }

debug/watchpoint_linux_amd64.go

@@ -8,10 +8,48 @@ package debug
 import (
 	"fmt"
 	"syscall"
+	"unsafe"
 )
 
 // Hardware watchpoint support via x86-64 debug registers (DR0-DR3, DR7).
 
+// The kernel translates PTRACE_POKEUSER/PEEKUSER offsets inside
+// [offsetof(struct user, u_debugreg[0]), u_debugreg[7]] to DR0-DR7
+// (arch/x86/kernel/ptrace.c, arch_ptrace).  sys/user.h places u_debugreg at
+// 0x350: DR0-DR3 are 0x350/0x358/0x360/0x368, DR6 (status) is 0x380 and
+// DR7 (control) is 0x388.  Offsets below 0x350 write user_regs_struct
+// fields (r15 at 0x0, r10 at 0x38), not debug registers.
+const (
+	drOffset = 0x350 // offsetof(struct user, u_debugreg[0]), DR0
+	dr6Off   = 0x380 // offsetof(struct user, u_debugreg[6]), DR6
+	dr7Off   = 0x388 // offsetof(struct user, u_debugreg[7]), DR7
+)
+
+// archWatchpointAddr resolves the address of the watchpoint that fired.
+// x86 delivers si_addr = the instruction pointer of the trapping access
+// (arch/x86/kernel/ptrace.c send_sigtrap passes regs->ip), so the watched
+// data address is recovered from DR6's slot bits (B0-B3, positive polarity
+// through PEEKUSER) and the matching DR0-DR3.
+func archWatchpointAddr(s *Session, siAddr uint64) uint64 {
+	dr6, err := ptracePeekUser(s.pid, dr6Off)
+	if err != nil {
+		return siAddr
+	}
+	for slot := range 4 {
+		if dr6&(1<<slot) != 0 {
+			addr, err := ptracePeekUser(s.pid, drOffset+uintptr(slot*8))
+			if err == nil && addr != 0 {
+				return addr
+			}
+		}
+	}
+	return siAddr
+}
+
+// maxWatchpoints reports the number of hardware watchpoint slots the
+// architecture provides: four address registers, DR0-DR3.
+func maxWatchpoints() int { return 4 }
+
 // WatchpointType selects what triggers the watchpoint.
 type WatchpointType int
 
@@ -62,23 +100,11 @@ func (s *Session) SetWatchpoint(slot int, addr uint64, typ WatchpointType, size
 		return fmt.Errorf("debug: watchpoint size must be 1, 2, 4, or 8")
 	}
 
-	var drAddr uintptr
+	if err := ptracePokeUser(s.pid, drOffset+uintptr(slot*8), addr); err != nil {
-	switch slot {
-	case 0:
-		drAddr = 0x0
-	case 1:
-		drAddr = 0x8
-	case 2:
-		drAddr = 0x10
-	case 3:
-		drAddr = 0x18
-	}
-
-	if err := ptracePokeUser(s.pid, drAddr, addr); err != nil {
 		return fmt.Errorf("debug: set DR%d: %w", slot, err)
 	}
 
-	dr7, err := ptracePeekUser(s.pid, 0x38)
+	dr7, err := ptracePeekUser(s.pid, dr7Off)
 	if err != nil {
 		return fmt.Errorf("debug: read DR7: %w", err)
 	}
@@ -90,7 +116,7 @@ func (s *Session) SetWatchpoint(slot int, addr uint64, typ WatchpointType, size
 	mask := ^((uint64(1) << (2 * slot)) | (uint64(3) << (16 + 4*slot)) | (uint64(3) << (18 + 4*slot)))
 	dr7 = (dr7 & mask) | enableBit | rwBits | lenField
 
-	if err := ptracePokeUser(s.pid, 0x38, dr7); err != nil {
+	if err := ptracePokeUser(s.pid, dr7Off, dr7); err != nil {
 		return fmt.Errorf("debug: set DR7: %w", err)
 	}
 	s.wpSlots[slot] = true
@@ -105,12 +131,12 @@ func (s *Session) ClearWatchpoint(slot int) error {
 	if !s.wpSlots[slot] {
 		return fmt.Errorf("debug: watchpoint slot %d is not in use", slot)
 	}
-	dr7, err := ptracePeekUser(s.pid, 0x38)
+	dr7, err := ptracePeekUser(s.pid, dr7Off)
 	if err != nil {
 		return err
 	}
 	dr7 &^= uint64(1) << (2 * slot)
-	if err := ptracePokeUser(s.pid, 0x38, dr7); err != nil {
+	if err := ptracePokeUser(s.pid, dr7Off, dr7); err != nil {
 		return err
 	}
 	s.wpSlots[slot] = false
@@ -119,7 +145,7 @@ func (s *Session) ClearWatchpoint(slot int) error {
 
 // ClearAllWatchpoints removes all hardware watchpoints.
 func (s *Session) ClearAllWatchpoints() error {
-	for slot := range 4 {
+	for slot := range maxWatchpoints() {
 		if s.wpSlots[slot] {
 			if err := s.ClearWatchpoint(slot); err != nil {
 				return err
@@ -146,16 +172,21 @@ func ptracePokeUser(pid int, offset uintptr, val uint64) error {
 }
 
 func ptracePeekUser(pid int, offset uintptr) (uint64, error) {
+	// x86 PEEKUSR writes the word to the user-space pointer in data
+	// (arch/x86/kernel/ptrace.c uses put_user); passing 0 there fails with
+	// EFAULT, so the word is read through a real address.
 	const ptracePeekuser = 3
-	val, _, errno := syscall.Syscall6(
+	var word uint64
+	_, _, errno := syscall.Syscall6(
 		syscall.SYS_PTRACE,
 		uintptr(ptracePeekuser),
 		uintptr(pid),
 		offset,
-		0, 0, 0,
+		uintptr(unsafe.Pointer(&word)),
+		0, 0,
 	)
 	if errno != 0 {
 		return 0, errno
 	}
-	return uint64(val), nil
+	return word, nil
 }

debug/watchpoint_linux_arm64.go

@@ -12,7 +12,7 @@ import (
 )
 
 // Hardware watchpoint support via arm64 debug registers (DBGWVR/DBGWCR).
-// Accessed via PTRACE_SETREGSET with NT_ARM_HW_BREAK.
+// Accessed via PTRACE_GETREGSET/SETREGSET with NT_ARM_HW_WATCH.
 
 // WatchpointType selects what triggers the watchpoint.
 type WatchpointType int
@@ -22,26 +22,35 @@ const (
 	WatchRead  WatchpointType = 3
 )
 
-const maxWatchpoints = 16
+// maxWatchpoints reports the number of hardware watchpoint slots the
+// architecture provides: DBGWVR0-DBGWCR15.
+func maxWatchpoints() int { return 16 }
 
-// hwBreakState mirrors the kernel's struct user_hwdebug_state.
+// hwWatchState mirrors the kernel's struct user_hwdebug_state.
-type hwBreakState struct {
+type hwWatchState struct {
 	DbgInfo uint32
 	_pad    [4]byte
-	DbgRegs [16]hwBreakReg
+	DbgRegs [16]hwWatchReg
 }
 
-type hwBreakReg struct {
+type hwWatchReg struct {
 	Addr uint64
 	Ctrl uint64
 }
 
-const (
+// ntArmHWWatch is NT_ARM_HW_WATCH (0x403), the watchpoint regset
-	ntArmHWBreak = 0x403 // NT_ARM_HW_BREAK
+// (include/uapi/linux/elf.h; 0x402 is NT_ARM_HW_BREAK).  Watchpoints and
-)
+// breakpoints live in different regsets with the same struct shape, so the
+// constant is named for what it arms to keep a future edit from arming
+// breakpoints instead.
+const ntArmHWWatch = 0x403
+
+// archWatchpointAddr resolves the address of the watchpoint that fired:
+// the arm64 kernel already reports the watched data address as si_addr.
+func archWatchpointAddr(s *Session, siAddr uint64) uint64 { return siAddr }
 
 func (s *Session) FindFreeWatchpointSlot() int {
-	for i := range maxWatchpoints {
+	for i := range maxWatchpoints() {
 		if !s.wpSlots[i] {
 			return i
 		}
@@ -50,7 +59,7 @@ func (s *Session) FindFreeWatchpointSlot() int {
 }
 
 func (s *Session) IsWatchpointSlotUsed(slot int) bool {
-	if slot < 0 || slot >= maxWatchpoints {
+	if slot < 0 || slot >= maxWatchpoints() {
 		return false
 	}
 	return s.wpSlots[slot]
@@ -58,27 +67,31 @@ func (s *Session) IsWatchpointSlotUsed(slot int) bool {
 
 // SetWatchpoint installs a hardware watchpoint on the given address.
 func (s *Session) SetWatchpoint(slot int, addr uint64, typ WatchpointType, size int) error {
-	if slot < 0 || slot >= maxWatchpoints {
+	if slot < 0 || slot >= maxWatchpoints() {
-		return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints-1)
+		return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints()-1)
 	}
 	if s.wpSlots[slot] {
 		return fmt.Errorf("debug: watchpoint slot %d already in use", slot)
 	}
 
-	state, err := s.getHWBreakState()
+	state, err := s.getHWWatchState()
 	if err != nil {
 		return fmt.Errorf("debug: read watchpoint state: %w", err)
 	}
 
-	if uint32(slot) >= state.DbgInfo {
+	// MDSCR_EL1 packs (debug_arch << 8) | num_slots into dbg_info, so only
-		return fmt.Errorf("debug: slot %d exceeds available watchpoints (%d)", slot, state.DbgInfo)
+	// the low byte counts slots.
+	if uint32(slot) >= state.DbgInfo&0xff {
+		return fmt.Errorf("debug: slot %d exceeds available watchpoints (%d)", slot, state.DbgInfo&0xff)
 	}
 
 	state.DbgRegs[slot].Addr = addr
+	// DBGWCR bits 3-4 select the access type: 01 load, 10 store, 11 either
+	// (ARM DDI 0487, DBGWCR<n>_EL1 watchpoint type field).
 	ctrl := uint64(1) // enable
 	switch typ {
 	case WatchWrite:
-		ctrl |= 1 << 3 // store only
+		ctrl |= 2 << 3 // store only
 	case WatchRead:
 		ctrl |= 3 << 3 // load+store
 	}
@@ -98,7 +111,7 @@ func (s *Session) SetWatchpoint(slot int, addr uint64, typ WatchpointType, size
 	ctrl |= bas << 5
 	state.DbgRegs[slot].Ctrl = ctrl
 
-	if err := s.setHWBreakState(state); err != nil {
+	if err := s.setHWWatchState(state); err != nil {
 		return fmt.Errorf("debug: set watchpoint: %w", err)
 	}
 
@@ -107,20 +120,20 @@ func (s *Session) SetWatchpoint(slot int, addr uint64, typ WatchpointType, size
 }
 
 func (s *Session) ClearWatchpoint(slot int) error {
-	if slot < 0 || slot >= maxWatchpoints {
+	if slot < 0 || slot >= maxWatchpoints() {
-		return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints-1)
+		return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints()-1)
 	}
 	if !s.wpSlots[slot] {
 		return fmt.Errorf("debug: watchpoint slot %d is not in use", slot)
 	}
 
-	state, err := s.getHWBreakState()
+	state, err := s.getHWWatchState()
 	if err != nil {
 		return err
 	}
 	state.DbgRegs[slot].Addr = 0
 	state.DbgRegs[slot].Ctrl = 0
-	if err := s.setHWBreakState(state); err != nil {
+	if err := s.setHWWatchState(state); err != nil {
 		return err
 	}
 	s.wpSlots[slot] = false
@@ -128,7 +141,7 @@ func (s *Session) ClearWatchpoint(slot int) error {
 }
 
 func (s *Session) ClearAllWatchpoints() error {
-	for slot := 0; slot < maxWatchpoints; slot++ {
+	for slot := range maxWatchpoints() {
 		if s.wpSlots[slot] {
 			if err := s.ClearWatchpoint(slot); err != nil {
 				return err
@@ -138,8 +151,8 @@ func (s *Session) ClearAllWatchpoints() error {
 	return nil
 }
 
-func (s *Session) getHWBreakState() (*hwBreakState, error) {
+func (s *Session) getHWWatchState() (*hwWatchState, error) {
-	var state hwBreakState
+	var state hwWatchState
 	iovec := syscall.Iovec{
 		Base: (*byte)(unsafe.Pointer(&state)),
 		Len:  uint64(unsafe.Sizeof(state)),
@@ -148,7 +161,7 @@ func (s *Session) getHWBreakState() (*hwBreakState, error) {
 		syscall.SYS_PTRACE,
 		uintptr(syscall.PTRACE_GETREGSET),
 		uintptr(s.pid),
-		uintptr(ntArmHWBreak),
+		uintptr(ntArmHWWatch),
 		uintptr(unsafe.Pointer(&iovec)),
 		0, 0,
 	)
@@ -158,7 +171,7 @@ func (s *Session) getHWBreakState() (*hwBreakState, error) {
 	return &state, nil
 }
 
-func (s *Session) setHWBreakState(state *hwBreakState) error {
+func (s *Session) setHWWatchState(state *hwWatchState) error {
 	iovec := syscall.Iovec{
 		Base: (*byte)(unsafe.Pointer(state)),
 		Len:  uint64(unsafe.Sizeof(*state)),
@@ -167,7 +180,7 @@ func (s *Session) setHWBreakState(state *hwBreakState) error {
 		syscall.SYS_PTRACE,
 		uintptr(syscall.PTRACE_SETREGSET),
 		uintptr(s.pid),
-		uintptr(ntArmHWBreak),
+		uintptr(ntArmHWWatch),
 		uintptr(unsafe.Pointer(&iovec)),
 		0, 0,
 	)

debug/watchpoint_linux_loong64.go

@@ -8,10 +8,47 @@ package debug
 import (
 	"fmt"
 	"syscall"
+	"unsafe"
 )
 
-// Hardware watchpoint support for LoongArch via debug registers.
+// Hardware watchpoint support via the NT_LOONGARCH_HW_WATCH regset.
-// Uses PTRACE_POKEUSER/PEEKUSER to access HW watchpoint registers.
+//
+// The kernel's PTRACE_POKEUSER on loong64 accepts only the user_pt_regs
+// indices 0-34 (GPRs, orig_a0, era, badv, per
+// arch/loongarch/include/uapi/asm/ptrace.h), so there is no debug-register
+// window to poke.  The real interface is PTRACE_GETREGSET/SETREGSET on
+// NT_LOONGARCH_HW_WATCH (0xa06, include/uapi/linux/elf.h) with struct
+// user_watch_state_v2 (arch/loongarch/include/uapi/asm/ptrace.h): a dbg_info
+// word followed by 14 slots of {addr u64, mask u64, ctrl u32, pad u32}.
+// hw_break_get puts the slot count in the low byte of dbg_info
+// (arch/loongarch/kernel/ptrace.c, ptrace_hbp_get_resource_info) and
+// hw_break_set ignores dbg_info, reading addr, mask and ctrl per slot.
+
+const ntLoongHWWatch = 0xa06
+
+// loongWatchState mirrors the kernel's struct user_watch_state_v2.
+type loongWatchState struct {
+	DbgInfo uint64
+	DbgRegs [14]loongWatchReg
+}
+
+type loongWatchReg struct {
+	Addr uint64
+	Mask uint64
+	Ctrl uint32
+	Pad  uint32
+}
+
+// Control word bit layout (arch/loongarch/include/asm/hw_breakpoint.h):
+// bits 1-4 privilege enables (CTRL_PLV3_ENABLE, 0x10, covers user mode),
+// bits 8-9 access type (LOAD 1<<0, STORE 1<<1), bits 10-11 length
+// (0=8 bytes, 1=4, 2=2, 3=1, inverted like the hardware FWP cfg).
+const (
+	loongCtrlPLV3Enable = 0x10
+	loongTypeLoad       = 1 << 8
+	loongTypeStore      = 2 << 8
+	loongLenShift       = 10
+)
 
 // WatchpointType selects what triggers the watchpoint.
 type WatchpointType int
@@ -21,10 +58,16 @@ const (
 	WatchRead  WatchpointType = 3
 )
 
-const maxWatchpoints = 4
+// maxWatchpoints reports the slot capacity of the regset struct; the number
+// the hardware actually provides is read from dbg_info at arm time.
+func maxWatchpoints() int { return len(loongWatchState{}.DbgRegs) }
+
+// archWatchpointAddr resolves the address of the watchpoint that fired:
+// the loongarch kernel already reports the accessed address as si_addr.
+func archWatchpointAddr(s *Session, siAddr uint64) uint64 { return siAddr }
 
 func (s *Session) FindFreeWatchpointSlot() int {
-	for i := range maxWatchpoints {
+	for i := range maxWatchpoints() {
 		if !s.wpSlots[i] {
 			return i
 		}
@@ -33,53 +76,56 @@ func (s *Session) FindFreeWatchpointSlot() int {
 }
 
 func (s *Session) IsWatchpointSlotUsed(slot int) bool {
-	if slot < 0 || slot >= maxWatchpoints {
+	if slot < 0 || slot >= maxWatchpoints() {
 		return false
 	}
 	return s.wpSlots[slot]
 }
 
-// SetWatchpoint installs a hardware watchpoint.
+// SetWatchpoint installs a hardware watchpoint on the given address.
 func (s *Session) SetWatchpoint(slot int, addr uint64, typ WatchpointType, size int) error {
-	if slot < 0 || slot >= maxWatchpoints {
+	if slot < 0 || slot >= maxWatchpoints() {
-		return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints-1)
+		return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints()-1)
 	}
 	if s.wpSlots[slot] {
 		return fmt.Errorf("debug: watchpoint slot %d already in use", slot)
 	}
-	if size != 1 && size != 2 && size != 4 && size != 8 {
+
+	var ctrlType uint32
+	switch typ {
+	case WatchWrite:
+		ctrlType = loongTypeStore
+	case WatchRead:
+		ctrlType = loongTypeLoad | loongTypeStore
+	}
+	var lenBits uint32
+	switch size {
+	case 1:
+		lenBits = 3
+	case 2:
+		lenBits = 2
+	case 4:
+		lenBits = 1
+	case 8:
+		lenBits = 0
+	default:
 		return fmt.Errorf("debug: watchpoint size must be 1, 2, 4, or 8")
 	}
 
-	// LoongArch debug registers: DBGWVR (watchpoint value) and DBGWCR (watchpoint control).
+	state, err := s.getLoongWatchState()
-	// Accessed via PTRACE_POKEUSER at architecture-specific offsets.
+	if err != nil {
-	if err := ptracePokeUser(s.pid, uintptr(0x1000+slot*8), addr); err != nil {
+		return fmt.Errorf("debug: read watchpoint state: %w", err)
-		return fmt.Errorf("debug: set watchpoint address: %w", err)
+	}
+	if uint64(slot) >= state.DbgInfo&0xff {
+		return fmt.Errorf("debug: slot %d exceeds available watchpoints (%d)", slot, state.DbgInfo&0xff)
 	}
 
-	// DBGWCR: enable + type + size.
+	state.DbgRegs[slot].Addr = addr
-	var wcr uint64 = 1 // enable
+	state.DbgRegs[slot].Mask = 0
-	switch typ {
+	state.DbgRegs[slot].Ctrl = loongCtrlPLV3Enable | ctrlType | lenBits<<loongLenShift
-	case WatchWrite:
-		wcr |= 1 << 3 // store
-	case WatchRead:
-		wcr |= 3 << 3 // load+store
-	}
-	var sizeBits uint64
-	switch size {
-	case 1:
-		sizeBits = 0
-	case 2:
-		sizeBits = 1
-	case 4:
-		sizeBits = 2
-	case 8:
-		sizeBits = 3
-	}
-	wcr |= sizeBits << 5
 
-	if err := ptracePokeUser(s.pid, uintptr(0x1001+slot*8), wcr); err != nil {
+	if err := s.setLoongWatchState(state); err != nil {
-		return fmt.Errorf("debug: set watchpoint control: %w", err)
+		return fmt.Errorf("debug: set watchpoint: %w", err)
 	}
 
 	s.wpSlots[slot] = true
@@ -87,14 +133,21 @@ func (s *Session) SetWatchpoint(slot int, addr uint64, typ WatchpointType, size
 }
 
 func (s *Session) ClearWatchpoint(slot int) error {
-	if slot < 0 || slot >= maxWatchpoints {
+	if slot < 0 || slot >= maxWatchpoints() {
-		return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints-1)
+		return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints()-1)
 	}
 	if !s.wpSlots[slot] {
 		return fmt.Errorf("debug: watchpoint slot %d is not in use", slot)
 	}
 
-	if err := ptracePokeUser(s.pid, uintptr(0x1001+slot*8), 0); err != nil {
+	state, err := s.getLoongWatchState()
+	if err != nil {
+		return err
+	}
+	state.DbgRegs[slot].Addr = 0
+	state.DbgRegs[slot].Mask = 0
+	state.DbgRegs[slot].Ctrl = 0
+	if err := s.setLoongWatchState(state); err != nil {
 		return err
 	}
 	s.wpSlots[slot] = false
@@ -102,7 +155,7 @@ func (s *Session) ClearWatchpoint(slot int) error {
 }
 
 func (s *Session) ClearAllWatchpoints() error {
-	for slot := 0; slot < maxWatchpoints; slot++ {
+	for slot := range maxWatchpoints() {
 		if s.wpSlots[slot] {
 			if err := s.ClearWatchpoint(slot); err != nil {
 				return err
@@ -112,14 +165,37 @@ func (s *Session) ClearAllWatchpoints() error {
 	return nil
 }
 
-func ptracePokeUser(pid int, offset uintptr, val uint64) error {
+func (s *Session) getLoongWatchState() (*loongWatchState, error) {
-	const ptracePokeuser = 6
+	var state loongWatchState
+	iovec := syscall.Iovec{
+		Base: (*byte)(unsafe.Pointer(&state)),
+		Len:  uint64(unsafe.Sizeof(state)),
+	}
 	_, _, errno := syscall.Syscall6(
 		syscall.SYS_PTRACE,
-		uintptr(ptracePokeuser),
+		uintptr(syscall.PTRACE_GETREGSET),
-		uintptr(pid),
+		uintptr(s.pid),
-		offset,
+		uintptr(ntLoongHWWatch),
-		uintptr(val),
+		uintptr(unsafe.Pointer(&iovec)),
+		0, 0,
+	)
+	if errno != 0 {
+		return nil, errno
+	}
+	return &state, nil
+}
+
+func (s *Session) setLoongWatchState(state *loongWatchState) error {
+	iovec := syscall.Iovec{
+		Base: (*byte)(unsafe.Pointer(state)),
+		Len:  uint64(unsafe.Sizeof(*state)),
+	}
+	_, _, errno := syscall.Syscall6(
+		syscall.SYS_PTRACE,
+		uintptr(syscall.PTRACE_SETREGSET),
+		uintptr(s.pid),
+		uintptr(ntLoongHWWatch),
+		uintptr(unsafe.Pointer(&iovec)),
 		0, 0,
 	)
 	if errno != 0 {
@@ -127,18 +203,3 @@ func ptracePokeUser(pid int, offset uintptr, val uint64) error {
 	}
 	return nil
 }
-
-func ptracePeekUser(pid int, offset uintptr) (uint64, error) {
-	const ptracePeekuser = 3
-	val, _, errno := syscall.Syscall6(
-		syscall.SYS_PTRACE,
-		uintptr(ptracePeekuser),
-		uintptr(pid),
-		offset,
-		0, 0, 0,
-	)
-	if errno != 0 {
-		return 0, errno
-	}
-	return uint64(val), nil
-}

debug/watchpoint_linux_riscv64.go

@@ -7,11 +7,16 @@ package debug
 
 import (
 	"fmt"
-	"syscall"
 )
 
-// Hardware watchpoint support for RISC-V via Sdtrig trigger registers.
+// Hardware watchpoints are not reachable through the riscv64 kernel ptrace
-// Uses PTRACE_POKEUSER/PEEKUSER to access debug registers.
+// interface.  arch/riscv/kernel/ptrace.c forwards every POKEUSER/PEEKUSER to
+// the generic ptrace_request, and the riscv user_regset view contains only
+// the GPR, FP and vector regsets: there is no debug-register or trigger
+// regset, and offsets outside the view fail with EIO.  The Sdtrig CSRs
+// (tselect/tdata1/tdata2) are not exposed to ptrace either.  Until the
+// kernel grows a trigger regset, SetWatchpoint reports the fact instead of
+// poking a window that does not exist.
 
 // WatchpointType selects what triggers the watchpoint.
 type WatchpointType int
@@ -21,10 +26,18 @@ const (
 	WatchRead  WatchpointType = 3
 )
 
-const maxWatchpoints = 4
+// maxWatchpoints reports the number of hardware watchpoint slots the
+// architecture provides.  riscv64 exposes none via ptrace; the bound exists
+// so the slot bookkeeping stays consistent.
+func maxWatchpoints() int { return 4 }
+
+// archWatchpointAddr resolves the address of the watchpoint that fired.
+// Unreachable in practice (watchpoints cannot be armed), but si_addr names
+// the accessed address where the kernel does report one.
+func archWatchpointAddr(s *Session, siAddr uint64) uint64 { return siAddr }
 
 func (s *Session) FindFreeWatchpointSlot() int {
-	for i := range maxWatchpoints {
+	for i := range maxWatchpoints() {
 		if !s.wpSlots[i] {
 			return i
 		}
@@ -33,115 +46,26 @@ func (s *Session) FindFreeWatchpointSlot() int {
 }
 
 func (s *Session) IsWatchpointSlotUsed(slot int) bool {
-	if slot < 0 || slot >= maxWatchpoints {
+	if slot < 0 || slot >= maxWatchpoints() {
 		return false
 	}
 	return s.wpSlots[slot]
 }
 
-// SetWatchpoint installs a hardware watchpoint.
+// SetWatchpoint always fails: the riscv64 kernel ptrace interface has no
+// hardware-watchpoint access.
 func (s *Session) SetWatchpoint(slot int, addr uint64, typ WatchpointType, size int) error {
-	if slot < 0 || slot >= maxWatchpoints {
+	return fmt.Errorf("debug: hardware watchpoints are not supported by the riscv64 kernel ptrace interface")
-		return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints-1)
-	}
-	if s.wpSlots[slot] {
-		return fmt.Errorf("debug: watchpoint slot %d already in use", slot)
-	}
-	if size != 1 && size != 2 && size != 4 && size != 8 {
-		return fmt.Errorf("debug: watchpoint size must be 1, 2, 4, or 8")
-	}
-
-	// RISC-V trigger registers: tdata1 encodes type/control, tdata2 holds address.
-	// The exact encoding depends on the trigger implementation (Sdtrig).
-	// Use PTRACE_POKEUSER to write to the trigger CSRs via the kernel's
-	// debug register interface.
-	if err := ptracePokeUser(s.pid, uintptr(0x1000+slot*8), addr); err != nil {
-		return fmt.Errorf("debug: set watchpoint address: %w", err)
-	}
-
-	// tdata1: set match control.  Mode=2 (data match), select=0, action=1 (debug exception).
-	var tdata1 uint64 = 2 << 60 // type = match (2)
-	tdata1 |= 1 << 0            // action = enter debug mode
-	tdata1 |= 1 << 7            // store (write) trigger
-	if typ == WatchRead {
-		tdata1 |= 1 << 6 // load trigger
-	}
-	// Size encoding: 0=1byte, 1=2byte, 2=4byte, 3=8byte.
-	var sizeBits uint64
-	switch size {
-	case 1:
-		sizeBits = 0
-	case 2:
-		sizeBits = 1
-	case 4:
-		sizeBits = 2
-	case 8:
-		sizeBits = 3
-	}
-	tdata1 |= sizeBits << 16 // size field
-
-	if err := ptracePokeUser(s.pid, uintptr(0x1001+slot*8), tdata1); err != nil {
-		return fmt.Errorf("debug: set watchpoint control: %w", err)
-	}
-
-	s.wpSlots[slot] = true
-	return nil
 }
 
+// ClearWatchpoint always fails: no watchpoint can ever be armed.
 func (s *Session) ClearWatchpoint(slot int) error {
-	if slot < 0 || slot >= maxWatchpoints {
+	if slot < 0 || slot >= maxWatchpoints() {
-		return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints-1)
+		return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints()-1)
 	}
-	if !s.wpSlots[slot] {
+	return fmt.Errorf("debug: watchpoint slot %d is not in use", slot)
-		return fmt.Errorf("debug: watchpoint slot %d is not in use", slot)
-	}
-
-	// Disable by clearing tdata1.
-	if err := ptracePokeUser(s.pid, uintptr(0x1001+slot*8), 0); err != nil {
-		return err
-	}
-	s.wpSlots[slot] = false
-	return nil
 }
 
 func (s *Session) ClearAllWatchpoints() error {
-	for slot := 0; slot < maxWatchpoints; slot++ {
-		if s.wpSlots[slot] {
-			if err := s.ClearWatchpoint(slot); err != nil {
-				return err
-			}
-		}
-	}
 	return nil
 }
-
-func ptracePokeUser(pid int, offset uintptr, val uint64) error {
-	const ptracePokeuser = 6
-	_, _, errno := syscall.Syscall6(
-		syscall.SYS_PTRACE,
-		uintptr(ptracePokeuser),
-		uintptr(pid),
-		offset,
-		uintptr(val),
-		0, 0,
-	)
-	if errno != 0 {
-		return errno
-	}
-	return nil
-}
-
-func ptracePeekUser(pid int, offset uintptr) (uint64, error) {
-	const ptracePeekuser = 3
-	val, _, errno := syscall.Syscall6(
-		syscall.SYS_PTRACE,
-		uintptr(ptracePeekuser),
-		uintptr(pid),
-		offset,
-		0, 0, 0,
-	)
-	if errno != 0 {
-		return 0, errno
-	}
-	return uint64(val), nil
-}