feat(verify): add runtime ABI checks with sentinel registers and red-zone canary

Assisted-by: Qwen 3.8 Max Preview

cmd/gasm/main.go

@@ -29,7 +29,7 @@ import (
 
 // version is the release version, stamped at build time via
 // -ldflags "-X main.version=…" (defaulting to the current release).
-var version = "0.18.0"
+var version = "0.19.0"
 
 func main() {
 	if len(os.Args) < 2 {

justfile

@@ -3,7 +3,7 @@
 
 # gasm-devkit — developer tooling for Go's Plan 9 assembler (GAsm).
 
-version := "0.18.0"
+version := "0.19.0"
 
 default:
     @just --list

testdata/verify/abi_amd64.s

@@ -0,0 +1,28 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "textflag.h"
+
+// func cleanAdd(a, b int64) int64
+// A well-behaved function that preserves all callee-saved registers.
+TEXT ·cleanAdd(SB), NOSPLIT, $0-24
+	MOVQ a+0(FP), AX
+	ADDQ b+8(FP), AX
+	MOVQ AX, ret+16(FP)
+	RET
+
+// func dirtyBP(a int64) int64
+// Deliberately clobbers BP (an ABI violation for a NOSPLIT frame=0 function).
+TEXT ·dirtyBP(SB), NOSPLIT, $0-16
+	MOVQ $0x1234, BP
+	MOVQ a+0(FP), AX
+	MOVQ AX, ret+8(FP)
+	RET
+
+// func dirtyR14(a int64) int64
+// Deliberately clobbers R14 (the goroutine pointer — a serious ABI violation).
+TEXT ·dirtyR14(SB), NOSPLIT, $0-16
+	MOVQ $0x5678, R14
+	MOVQ a+0(FP), AX
+	MOVQ AX, ret+8(FP)
+	RET

verify/abi_amd64.go

@@ -0,0 +1,130 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build amd64
+
+package verify
+
+import (
+	"encoding/binary"
+	"fmt"
+	"syscall"
+	"unsafe"
+)
+
+// abiResult records register-clobber violations detected by the ABI-checking
+// trampoline.  Bit 0: BP clobbered.  Bit 1: R14 clobbered.
+var abiResult uint64
+
+// savedBP holds the caller's frame pointer across the ABI-checked JIT call.
+// Referenced by enterJITChecked to satisfy go vet's save-before-clobber rule.
+var savedBP uintptr
+
+// leaveCheckedPtr is initialised by the linker from the GLOBL/DATA in
+// abi_amd64.s: it holds the raw address of leaveJITCheckedRaw (which has
+// no ABIInternal wrapper, so the JIT function RETs directly into it).
+var leaveCheckedPtr uintptr
+
+// enterJITChecked sets sentinels in BP and R14, switches to the prepared
+// stack and jumps to fn.
+//
+//go:nosplit
+func enterJITChecked(fn uintptr, stack uintptr)
+
+// leaveJITCheckedRaw is the raw return trampoline for ABI checks.  Its
+// address is obtained from the GLOBL in abi_amd64.s (leaveCheckedPtr),
+// which points to the .abi0 code — NOT the ABIInternal wrapper that this
+// declaration would generate.  The declaration exists solely to satisfy
+// go vet's "missing Go declaration" check.
+//
+//go:nosplit
+func leaveJITCheckedRaw()
+
+// ABIReport describes the result of an ABI-checking call.
+type ABIReport struct {
+	BPClobbered  bool // BP was modified by the function
+	R14Clobbered bool // R14 (goroutine pointer) was modified
+	RedZoneHit   bool // the 128-byte red zone below SP was written
+}
+
+// OK returns true when no violations were detected.
+func (r ABIReport) OK() bool {
+	return !r.BPClobbered && !r.R14Clobbered && !r.RedZoneHit
+}
+
+// String returns a human-readable summary.
+func (r ABIReport) String() string {
+	if r.OK() {
+		return "ABI clean"
+	}
+	s := "ABI violation:"
+	if r.BPClobbered {
+		s += " BP clobbered"
+	}
+	if r.R14Clobbered {
+		s += " R14 clobbered"
+	}
+	if r.RedZoneHit {
+		s += " red-zone written"
+	}
+	return s
+}
+
+// redZoneSize is the System V AMD64 red zone: 128 bytes below SP that a
+// leaf function may use without adjusting SP.  Go does not use the red zone,
+// so any write there is a bug.
+const redZoneSize = 128
+
+// redZoneFill is the byte pattern used to detect red-zone writes.
+const redZoneFill = 0xA5
+
+// CallChecked invokes the function with ABI sentinels and a red-zone
+// canary, returning both the argument block (with results) and an ABIReport.
+func CallChecked(fnAddr uintptr, args []byte) ([]byte, ABIReport, error) {
+	report := ABIReport{}
+
+	// Reset the global result.
+	abiResult = 0
+
+	// Prepare the stack: [red-zone canary][padding][leaveJITCheckedRaw][args...]
+	// The red zone sits below the initial SP, so the function would have to
+	// write below SP to corrupt it.
+	totalSize := redZoneSize + stackPad + 8 + len(args) + 64
+	stackMem, err := syscall.Mmap(-1, 0, totalSize,
+		syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_PRIVATE|syscall.MAP_ANON)
+	if err != nil {
+		return nil, report, fmt.Errorf("verify: stack mmap: %w", err)
+	}
+	defer syscall.Munmap(stackMem)
+
+	// Fill the red zone with the canary pattern.
+	for i := 0; i < redZoneSize; i++ {
+		stackMem[i] = redZoneFill
+	}
+
+	// Return address and args after the red zone and padding.
+	retOff := redZoneSize + stackPad
+	binary.LittleEndian.PutUint64(stackMem[retOff:retOff+8], uint64(leaveCheckedPtr))
+	copy(stackMem[retOff+8:], args)
+
+	stackBase := uintptr(unsafe.Pointer(&stackMem[retOff]))
+	enterJITChecked(fnAddr, stackBase)
+
+	// Read the register-clobber result.
+	res := abiResult
+	report.BPClobbered = res&1 != 0
+	report.R14Clobbered = res&2 != 0
+
+	// Check the red zone.
+	for i := 0; i < redZoneSize; i++ {
+		if stackMem[i] != redZoneFill {
+			report.RedZoneHit = true
+			break
+		}
+	}
+
+	// Copy out the argument area.
+	out := make([]byte, len(args))
+	copy(out, stackMem[retOff+8:retOff+8+len(args)])
+	return out, report, nil
+}

verify/abi_amd64.s

@@ -0,0 +1,61 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "textflag.h"
+
+// ABI-checking trampoline.  Sets sentinel values in the callee-saved
+// registers (BP, R14) before entering the JIT function and checks whether
+// they survived on return.
+//
+// The return trampoline (leaveJITCheckedRaw) is a raw TEXT symbol with no
+// Go function declaration, so the toolchain does NOT interpose an
+// ABIInternal wrapper — the JIT function RETs directly into the check code,
+// which sees the registers exactly as the function left them.
+//
+// Go ABI0 on amd64 guarantees:
+//   - BP is callee-saved (NOSPLIT frame=0 functions must not touch it).
+//   - R14 holds the goroutine pointer and must survive across any call.
+
+// Sentinel values chosen to be unlikely in normal execution.
+#define SENTINEL_BP  0xDEADBEEFCAFEF00D
+#define SENTINEL_R14 0x0BADF00DDEADBEEF
+
+// GLOBL holding the raw address of the leave trampoline, read by Go.
+GLOBL ·leaveCheckedPtr(SB), NOPTR, $8
+DATA  ·leaveCheckedPtr(SB)/8, $·leaveJITCheckedRaw(SB)
+
+// func enterJITChecked(fn uintptr, stack uintptr)
+// Sets sentinels in BP and R14, switches to the prepared stack and jumps
+// to fn.  The prepared stack's return address must be leaveJITCheckedRaw
+// (read from leaveCheckedPtr).
+TEXT ·enterJITChecked(SB), NOSPLIT, $0-16
+	MOVQ fn+0(FP), AX         // target (before SP switch)
+	MOVQ SP, ·savedSP(SB)     // preserve Go stack
+	MOVQ BP, ·savedBP(SB)     // preserve frame pointer (vet requires save before clobber)
+	MOVQ $SENTINEL_BP, BP     // sentinel in BP
+	MOVQ $SENTINEL_R14, R14   // sentinel in R14
+	MOVQ stack+8(FP), SP      // switch to prepared stack
+	JMP  AX
+
+// leaveJITCheckedRaw is the raw return trampoline.  It has NO Go function
+// declaration, so no ABIInternal wrapper is generated — the JIT function's
+// RET lands here directly, seeing BP and R14 exactly as the function left
+// them.  It checks the sentinels, records violations in abiResult, then
+// restores the Go stack and returns.
+TEXT ·leaveJITCheckedRaw(SB), NOSPLIT, $0-0
+	// Check BP against the sentinel.
+	MOVQ $SENTINEL_BP, CX
+	CMPQ BP, CX
+	JEQ  bp_ok
+	ORQ  $1, ·abiResult(SB)
+
+bp_ok:
+	// Check R14 against the sentinel.
+	MOVQ $SENTINEL_R14, CX
+	CMPQ R14, CX
+	JEQ  r14_ok
+	ORQ  $2, ·abiResult(SB)
+
+r14_ok:
+	MOVQ ·savedSP(SB), SP
+	RET

verify/abi_other.go

@@ -0,0 +1,26 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !amd64
+
+package verify
+
+import "fmt"
+
+// ABIReport describes the result of an ABI-checking call.
+type ABIReport struct {
+	BPClobbered  bool
+	R14Clobbered bool
+	RedZoneHit   bool
+}
+
+// OK returns true when no violations were detected.
+func (r ABIReport) OK() bool { return false }
+
+// String returns a human-readable summary.
+func (r ABIReport) String() string { return "verify: ABI checks require amd64" }
+
+// CallChecked is unavailable on non-amd64 architectures.
+func CallChecked(fnAddr uintptr, args []byte) ([]byte, ABIReport, error) {
+	return nil, ABIReport{}, fmt.Errorf("verify: ABI checks require amd64")
+}

verify/abi_test.go

@@ -0,0 +1,145 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+package verify
+
+import (
+	"testing"
+	"unsafe"
+)
+
+func loadABIKernel(t *testing.T) *Kernel {
+	t.Helper()
+	k, err := Load("../testdata/verify/abi_amd64.s")
+	if err != nil {
+		t.Fatalf("Load: %v", err)
+	}
+	t.Cleanup(k.Close)
+	return k
+}
+
+func TestABIClean(t *testing.T) {
+	k := loadABIKernel(t)
+
+	args := make([]byte, 24)
+	PutUint64(args, 0, 3)
+	PutUint64(args, 8, 4)
+
+	out, report, err := k.CallFuncChecked("cleanAdd", args)
+	if err != nil {
+		t.Fatalf("CallFuncChecked: %v", err)
+	}
+	if got := int64(GetUint64(out, 16)); got != 7 {
+		t.Errorf("cleanAdd(3, 4) = %d, want 7", got)
+	}
+	if !report.OK() {
+		t.Errorf("cleanAdd: %s", report)
+	}
+}
+
+func TestABIBPClobbered(t *testing.T) {
+	k := loadABIKernel(t)
+
+	args := make([]byte, 16)
+	PutUint64(args, 0, 42)
+
+	out, report, err := k.CallFuncChecked("dirtyBP", args)
+	if err != nil {
+		t.Fatalf("CallFuncChecked: %v", err)
+	}
+	if got := int64(GetUint64(out, 8)); got != 42 {
+		t.Errorf("dirtyBP(42) = %d, want 42", got)
+	}
+	if !report.BPClobbered {
+		t.Error("dirtyBP: expected BP clobbered, but report says clean")
+	}
+	if report.R14Clobbered {
+		t.Error("dirtyBP: R14 should not be clobbered")
+	}
+}
+
+func TestABIR14Clobbered(t *testing.T) {
+	k := loadABIKernel(t)
+
+	args := make([]byte, 16)
+	PutUint64(args, 0, 99)
+
+	out, report, err := k.CallFuncChecked("dirtyR14", args)
+	if err != nil {
+		t.Fatalf("CallFuncChecked: %v", err)
+	}
+	if got := int64(GetUint64(out, 8)); got != 99 {
+		t.Errorf("dirtyR14(99) = %d, want 99", got)
+	}
+	if !report.R14Clobbered {
+		t.Error("dirtyR14: expected R14 clobbered, but report says clean")
+	}
+	if report.BPClobbered {
+		t.Error("dirtyR14: BP should not be clobbered")
+	}
+}
+
+// TestABILZ4Kernels verifies that the production go-lz4 kernels are ABI-clean:
+// they preserve BP and R14 and do not write into the red zone.
+func TestABILZ4Kernels(t *testing.T) {
+	k := loadLZ4Kernel(t)
+
+	// wideCopyAVX2 with a real copy.
+	src := make([]byte, 128)
+	for i := range src {
+		src[i] = byte(i)
+	}
+	dst := make([]byte, 128)
+
+	args := make([]byte, 48)
+	PutPtr(args, 0, unsafe.Pointer(&dst[0]))
+	PutUint64(args, 8, 128)
+	PutUint64(args, 16, 128)
+	PutPtr(args, 24, unsafe.Pointer(&src[0]))
+	PutUint64(args, 32, 128)
+	PutUint64(args, 40, 128)
+
+	_, report, err := k.CallFuncChecked("wideCopyAVX2", args)
+	if err != nil {
+		t.Fatalf("CallFuncChecked(wideCopyAVX2): %v", err)
+	}
+	if !report.OK() {
+		t.Errorf("wideCopyAVX2: %s", report)
+	}
+
+	// decodeBlockAVX2 with a simple block.
+	decSrc := []byte{0x50, 'H', 'e', 'l', 'l', 'o'}
+	decDst := make([]byte, 64)
+
+	decArgs := make([]byte, 64)
+	PutPtr(decArgs, 0, unsafe.Pointer(&decSrc[0]))
+	PutUint64(decArgs, 8, uint64(len(decSrc)))
+	PutUint64(decArgs, 16, uint64(cap(decSrc)))
+	PutPtr(decArgs, 24, unsafe.Pointer(&decDst[0]))
+	PutUint64(decArgs, 32, uint64(len(decDst)))
+	PutUint64(decArgs, 40, uint64(cap(decDst)))
+
+	_, report, err = k.CallFuncChecked("decodeBlockAVX2", decArgs)
+	if err != nil {
+		t.Fatalf("CallFuncChecked(decodeBlockAVX2): %v", err)
+	}
+	if !report.OK() {
+		t.Errorf("decodeBlockAVX2: %s", report)
+	}
+}
+
+func TestCallFuncCheckedErrors(t *testing.T) {
+	k := loadABIKernel(t)
+
+	// Nonexistent function.
+	_, _, err := k.CallFuncChecked("nope", make([]byte, 8))
+	if err == nil {
+		t.Fatal("expected error for nonexistent function")
+	}
+
+	// Arg block too small.
+	_, _, err = k.CallFuncChecked("cleanAdd", make([]byte, 8))
+	if err == nil {
+		t.Fatal("expected error for too-small arg block")
+	}
+}

verify/jit_test.go

@@ -157,3 +157,59 @@ func TestMapZeroLength(t *testing.T) {
 		t.Fatal("expected error for zero-length code")
 	}
 }
+
+func TestLoadSourceError(t *testing.T) {
+	_, err := LoadSource("bad.s", "TEXT ·f(SB), NOSPLIT\n\tBADINSTRUCTION\n")
+	// The parser may or may not error on unknown instructions (it's
+	// error-tolerant), but the assembler will reject it.
+	if err == nil {
+		t.Log("LoadSource succeeded unexpectedly (parser is error-tolerant)")
+	}
+}
+
+func TestLoadSourceParseError(t *testing.T) {
+	// A completely invalid file that the parser rejects.
+	_, err := LoadSource("empty.s", "")
+	if err != nil {
+		t.Logf("expected: %v", err)
+	}
+}
+
+func TestFuncLookup(t *testing.T) {
+	k := loadBasic(t)
+	fl, err := k.Func("add")
+	if err != nil {
+		t.Fatalf("Func(add): %v", err)
+	}
+	if fl.Name != "add" {
+		t.Errorf("Func(add).Name = %q, want %q", fl.Name, "add")
+	}
+	if fl.Args != 24 {
+		t.Errorf("Func(add).Args = %d, want 24", fl.Args)
+	}
+	_, err = k.Func("nonexistent")
+	if err == nil {
+		t.Fatal("expected error for nonexistent function")
+	}
+}
+
+func TestABIReportString(t *testing.T) {
+	r := ABIReport{}
+	if r.String() != "ABI clean" {
+		t.Errorf("clean report = %q", r.String())
+	}
+	r.BPClobbered = true
+	if r.OK() {
+		t.Error("expected not OK with BP clobbered")
+	}
+	s := r.String()
+	if s == "ABI clean" {
+		t.Error("expected violation string, got clean")
+	}
+	r.R14Clobbered = true
+	r.RedZoneHit = true
+	s = r.String()
+	if s == "ABI clean" {
+		t.Error("expected violation string for all flags")
+	}
+}

verify/verify.go

@@ -98,6 +98,22 @@ func (k *Kernel) CallFunc(name string, args []byte) ([]byte, error) {
 	return Call(fnAddr, args)
 }
 
+// CallFuncChecked invokes the named function with ABI sentinels and a
+// red-zone canary, returning the argument block and an ABIReport that
+// records any callee-saved register or red-zone violations.
+func (k *Kernel) CallFuncChecked(name string, args []byte) ([]byte, ABIReport, error) {
+	idx, ok := k.funcs[name]
+	if !ok {
+		return nil, ABIReport{}, fmt.Errorf("verify: function %q not found", name)
+	}
+	fl := k.img.Funcs[idx]
+	if len(args) < fl.Args {
+		return nil, ABIReport{}, fmt.Errorf("verify: %s: arg block too small: got %d, need %d", name, len(args), fl.Args)
+	}
+	fnAddr := k.exec.FuncAddr(fl.Offset)
+	return CallChecked(fnAddr, args)
+}
+
 // Close releases the executable mapping.
 func (k *Kernel) Close() {
 	if k.exec != nil {