feat(debug): port the debugger to FreeBSD
Assisted-by: GLM 5.3 Flash
This commit is contained in:
@@ -0,0 +1,205 @@
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// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
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// SPDX-License-Identifier: BSD-3-Clause
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//go:build freebsd && arm64
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package debug
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import (
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"fmt"
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"unsafe"
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"golang.org/x/sys/unix"
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)
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// Hardware watchpoint support via arm64 debug registers, read and written
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// as one blob through PT_GETDBREGS/PT_SETDBREGS. The FreeBSD struct dbreg
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// (sys/arm64/include/reg.h) opens with the debug-facility header and then
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// carries 16 breakpoint and 16 watchpoint pairs of {address, control}.
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// dbreg mirrors FreeBSD's struct dbreg for PT_GETDBREGS/PT_SETDBREGS.
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type dbreg struct {
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DbDebugVer uint8
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DbNbkpts uint8
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DbNwtpts uint8
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_ [5]byte
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DbBreakregs [16]struct {
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Addr uint64
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Ctrl uint32
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_ uint32
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}
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DbWatchregs [16]struct {
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Addr uint64
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Ctrl uint32
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_ uint32
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}
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}
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// WatchpointType selects what triggers the watchpoint.
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type WatchpointType int
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const (
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WatchWrite WatchpointType = 1 // trigger on write
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WatchRead WatchpointType = 3 // trigger on read or write
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)
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// maxWatchpoints reports the number of hardware watchpoint slots the
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// architecture provides: DBGWVR0-DBGWCR15.
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func maxWatchpoints() int { return 16 }
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// getDbRegs reads the debug register file of the stopped debuggee.
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func (s *Session) getDbRegs() (*dbreg, error) {
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var dr dbreg
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if _, _, errno := unix.Syscall6(
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unix.SYS_PTRACE,
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uintptr(unix.PT_GETDBREGS),
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uintptr(s.pid),
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0,
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uintptr(unsafe.Pointer(&dr)),
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0, 0,
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); errno != 0 {
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return nil, errno
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}
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return &dr, nil
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}
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// setDbRegs writes the debug register file of the stopped debuggee.
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func (s *Session) setDbRegs(dr *dbreg) error {
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if _, _, errno := unix.Syscall6(
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unix.SYS_PTRACE,
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uintptr(unix.PT_SETDBREGS),
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uintptr(s.pid),
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0,
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uintptr(unsafe.Pointer(dr)),
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0, 0,
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); errno != 0 {
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return errno
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}
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return nil
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}
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// archStopTrace classifies a TRAP_TRACE stop. On arm64 the kernel
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// delivers both the software single step and the watchpoint hit through
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// EXCP_SOFTSTP_EL0/EXCP_WATCHPT_EL0 with TRAP_TRACE (sys/arm64/arm64/
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// trap.c); the watchpoint address rides the FAR register, so a stop whose
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// reported address falls inside an armed watchpoint's byte range is a
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// watchpoint and everything else is a single step.
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func archStopTrace(s *Session, siAddr uint64) (StopReason, uint64) {
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dr, err := s.getDbRegs()
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if err != nil {
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return StopSingleStep, 0
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}
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for slot := range 16 {
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ctrl := uint64(dr.DbWatchregs[slot].Ctrl)
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if ctrl&1 == 0 || dr.DbWatchregs[slot].Addr == 0 {
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continue
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}
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if bas := (ctrl >> 5) & 0xFF; bas != 0 && siAddr >= dr.DbWatchregs[slot].Addr && siAddr < dr.DbWatchregs[slot].Addr+8 {
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return StopWatchpoint, siAddr
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}
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}
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return StopSingleStep, 0
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}
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// FindFreeWatchpointSlot returns the index of the first free watchpoint
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// slot, or -1 if all of them are in use.
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func (s *Session) FindFreeWatchpointSlot() int {
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for i := range maxWatchpoints() {
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if !s.wpSlots[i] {
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return i
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}
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}
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return -1
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}
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// IsWatchpointSlotUsed reports whether slot currently holds a watchpoint.
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func (s *Session) IsWatchpointSlotUsed(slot int) bool {
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if slot < 0 || slot >= maxWatchpoints() {
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return false
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}
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return s.wpSlots[slot]
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}
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// SetWatchpoint installs a hardware watchpoint on the given address. The
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// control word is the architectural DBGWCR (ARM DDI 0487): bit 0 enables,
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// bits 3-4 select the access type (10 store, 11 load+store) and bits 5-12
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// are the byte-address select, so the watch stays 8-byte aligned and names
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// its watched bytes through BAS.
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func (s *Session) SetWatchpoint(slot int, addr uint64, typ WatchpointType, size int) error {
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if slot < 0 || slot >= maxWatchpoints() {
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return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints()-1)
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}
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if s.wpSlots[slot] {
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return fmt.Errorf("debug: watchpoint slot %d already in use", slot)
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}
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var bas uint64
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switch size {
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case 1:
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bas = 0x01
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case 2:
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bas = 0x03
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case 4:
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bas = 0x0F
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case 8:
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bas = 0xFF
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default:
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return fmt.Errorf("debug: watchpoint size must be 1, 2, 4, or 8")
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}
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dr, err := s.getDbRegs()
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if err != nil {
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return fmt.Errorf("debug: read debug registers: %w", err)
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}
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if uint8(slot) >= dr.DbNwtpts && dr.DbNwtpts != 0 {
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return fmt.Errorf("debug: slot %d exceeds available watchpoints (%d)", slot, dr.DbNwtpts)
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}
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ctrl := uint64(1) // enable
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switch typ {
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case WatchWrite:
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ctrl |= 2 << 3 // store only
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case WatchRead:
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ctrl |= 3 << 3 // load+store
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}
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ctrl |= bas << 5
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dr.DbWatchregs[slot].Addr = addr
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dr.DbWatchregs[slot].Ctrl = uint32(ctrl)
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if err := s.setDbRegs(dr); err != nil {
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return fmt.Errorf("debug: set debug registers: %w", err)
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}
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s.wpSlots[slot] = true
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return nil
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}
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// ClearWatchpoint removes a hardware watchpoint.
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func (s *Session) ClearWatchpoint(slot int) error {
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if slot < 0 || slot >= maxWatchpoints() {
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return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints()-1)
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}
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if !s.wpSlots[slot] {
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return fmt.Errorf("debug: watchpoint slot %d is not in use", slot)
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}
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dr, err := s.getDbRegs()
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if err != nil {
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return err
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}
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dr.DbWatchregs[slot].Addr = 0
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dr.DbWatchregs[slot].Ctrl = 0
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if err := s.setDbRegs(dr); err != nil {
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return err
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}
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s.wpSlots[slot] = false
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return nil
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}
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// ClearAllWatchpoints removes all hardware watchpoints.
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func (s *Session) ClearAllWatchpoints() error {
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for slot := range maxWatchpoints() {
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if s.wpSlots[slot] {
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if err := s.ClearWatchpoint(slot); err != nil {
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return err
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}
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}
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}
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return nil
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}
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