gasm-sdk/debug/watchpoint_linux_riscv64.go

// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: BSD-3-Clause

//go:build linux && riscv64

package debug

import (
	"fmt"
)

// Hardware watchpoints are not reachable through the riscv64 kernel ptrace
// 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

const (
	WatchWrite WatchpointType = 1
	WatchRead  WatchpointType = 3
)

// 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() {
		if !s.wpSlots[i] {
			return i
		}
	}
	return -1
}

func (s *Session) IsWatchpointSlotUsed(slot int) bool {
	if slot < 0 || slot >= maxWatchpoints() {
		return false
	}
	return s.wpSlots[slot]
}

// 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 {
	return fmt.Errorf("debug: hardware watchpoints are not supported by the riscv64 kernel ptrace interface")
}

// ClearWatchpoint always fails: no watchpoint can ever be armed.
func (s *Session) ClearWatchpoint(slot int) error {
	if slot < 0 || slot >= maxWatchpoints() {
		return fmt.Errorf("debug: watchpoint slot must be 0-%d", maxWatchpoints()-1)
	}
	return fmt.Errorf("debug: watchpoint slot %d is not in use", slot)
}

func (s *Session) ClearAllWatchpoints() error {
	return nil
}