xref: /freebsd/lib/libproc/proc_bkpt.c (revision a2f733ab)

/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2010 The FreeBSD Foundation
 * All rights reserved.
 *
 * This software was developed by Rui Paulo under sponsorship from the
 * FreeBSD Foundation.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/types.h>
#include <sys/ptrace.h>
#include <sys/wait.h>

#include <assert.h>
#include <err.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>

#include "_libproc.h"

#if defined(__aarch64__)
#define	AARCH64_BRK		0xd4200000
#define	AARCH64_BRK_IMM16_SHIFT	5
#define	AARCH64_BRK_IMM16_VAL	(0xd << AARCH64_BRK_IMM16_SHIFT)
#define	BREAKPOINT_INSTR	(AARCH64_BRK | AARCH64_BRK_IMM16_VAL)
#define	BREAKPOINT_INSTR_SZ	4
#elif defined(__amd64__) || defined(__i386__)
#define	BREAKPOINT_INSTR	0xcc	/* int 0x3 */
#define	BREAKPOINT_INSTR_SZ	1
#define	BREAKPOINT_ADJUST_SZ	BREAKPOINT_INSTR_SZ
#elif defined(__arm__)
#define	BREAKPOINT_INSTR	0xe7ffffff	/* bkpt */
#define	BREAKPOINT_INSTR_SZ	4
#elif defined(__powerpc__)
#define	BREAKPOINT_INSTR	0x7fe00008	/* trap */
#define	BREAKPOINT_INSTR_SZ	4
#elif defined(__riscv)
#define	BREAKPOINT_INSTR	0x00100073	/* sbreak */
#define	BREAKPOINT_INSTR_SZ	4
#else
#error "Add support for your architecture"
#endif

/*
 * Use 4-bytes holder for breakpoint instruction on all the platforms.
 * Works for x86 as well until it is endian-little platform.
 * (We are coping one byte only on x86 from this 4-bytes piece of
 * memory).
 */
typedef uint32_t instr_t;

static int
proc_stop(struct proc_handle *phdl)
{
	int status;

	if (kill(proc_getpid(phdl), SIGSTOP) == -1) {
		DPRINTF("kill %d", proc_getpid(phdl));
		return (-1);
	} else if (waitpid(proc_getpid(phdl), &status, WSTOPPED) == -1) {
		DPRINTF("waitpid %d", proc_getpid(phdl));
		return (-1);
	} else if (!WIFSTOPPED(status)) {
		DPRINTFX("waitpid: unexpected status 0x%x", status);
		return (-1);
	}

	return (0);
}

int
proc_bkptset(struct proc_handle *phdl, uintptr_t address,
    unsigned long *saved)
{
	struct ptrace_io_desc piod;
	int ret = 0, stopped;
	instr_t instr;

	*saved = 0;
	if (phdl->status == PS_DEAD || phdl->status == PS_UNDEAD ||
	    phdl->status == PS_IDLE) {
		errno = ENOENT;
		return (-1);
	}

	DPRINTFX("adding breakpoint at 0x%lx", (unsigned long)address);

	stopped = 0;
	if (phdl->status != PS_STOP) {
		if (proc_stop(phdl) != 0)
			return (-1);
		stopped = 1;
	}

	/*
	 * Read the original instruction.
	 */
	instr = 0;
	piod.piod_op = PIOD_READ_I;
	piod.piod_offs = (void *)address;
	piod.piod_addr = &instr;
	piod.piod_len  = BREAKPOINT_INSTR_SZ;
	if (ptrace(PT_IO, proc_getpid(phdl), (caddr_t)&piod, 0) < 0) {
		DPRINTF("ERROR: couldn't read instruction at address 0x%jx",
		    (uintmax_t)address);
		ret = -1;
		goto done;
	}
	*saved = instr;
	/*
	 * Write a breakpoint instruction to that address.
	 */
	instr = BREAKPOINT_INSTR;
	piod.piod_op = PIOD_WRITE_I;
	piod.piod_offs = (void *)address;
	piod.piod_addr = &instr;
	piod.piod_len  = BREAKPOINT_INSTR_SZ;
	if (ptrace(PT_IO, proc_getpid(phdl), (caddr_t)&piod, 0) < 0) {
		DPRINTF("ERROR: couldn't write instruction at address 0x%jx",
		    (uintmax_t)address);
		ret = -1;
		goto done;
	}

done:
	if (stopped)
		/* Restart the process if we had to stop it. */
		proc_continue(phdl);

	return (ret);
}

int
proc_bkptdel(struct proc_handle *phdl, uintptr_t address,
    unsigned long saved)
{
	struct ptrace_io_desc piod;
	int ret = 0, stopped;
	instr_t instr;

	if (phdl->status == PS_DEAD || phdl->status == PS_UNDEAD ||
	    phdl->status == PS_IDLE) {
		errno = ENOENT;
		return (-1);
	}

	DPRINTFX("removing breakpoint at 0x%lx", (unsigned long)address);

	stopped = 0;
	if (phdl->status != PS_STOP) {
		if (proc_stop(phdl) != 0)
			return (-1);
		stopped = 1;
	}

	/*
	 * Overwrite the breakpoint instruction that we setup previously.
	 */
	instr = saved;
	piod.piod_op = PIOD_WRITE_I;
	piod.piod_offs = (void *)address;
	piod.piod_addr = &instr;
	piod.piod_len  = BREAKPOINT_INSTR_SZ;
	if (ptrace(PT_IO, proc_getpid(phdl), (caddr_t)&piod, 0) < 0) {
		DPRINTF("ERROR: couldn't write instruction at address 0x%jx",
		    (uintmax_t)address);
		ret = -1;
	}

	if (stopped)
		/* Restart the process if we had to stop it. */
		proc_continue(phdl);

	return (ret);
}

/*
 * Decrement pc so that we delete the breakpoint at the correct
 * address, i.e. at the BREAKPOINT_INSTR address.
 *
 * This is only needed on some architectures where the pc value
 * when reading registers points at the instruction after the
 * breakpoint, e.g. x86.
 */
void
proc_bkptregadj(unsigned long *pc)
{

	(void)pc;
#ifdef BREAKPOINT_ADJUST_SZ
	*pc = *pc - BREAKPOINT_ADJUST_SZ;
#endif
}

/*
 * Step over the breakpoint.
 */
int
proc_bkptexec(struct proc_handle *phdl, unsigned long saved)
{
	unsigned long pc;
	unsigned long samesaved;
	int status;

	if (proc_regget(phdl, REG_PC, &pc) < 0) {
		DPRINTFX("ERROR: couldn't get PC register");
		return (-1);
	}
	proc_bkptregadj(&pc);
	if (proc_bkptdel(phdl, pc, saved) < 0) {
		DPRINTFX("ERROR: couldn't delete breakpoint");
		return (-1);
	}
	/*
	 * Go back in time and step over the new instruction just
	 * set up by proc_bkptdel().
	 */
	proc_regset(phdl, REG_PC, pc);
	if (ptrace(PT_STEP, proc_getpid(phdl), (caddr_t)1, 0) < 0) {
		DPRINTFX("ERROR: ptrace step failed");
		return (-1);
	}
	proc_wstatus(phdl);
	status = proc_getwstat(phdl);
	if (!WIFSTOPPED(status)) {
		DPRINTFX("ERROR: don't know why process stopped");
		return (-1);
	}
	/*
	 * Restore the breakpoint. The saved instruction should be
	 * the same as the one that we were passed in.
	 */
	if (proc_bkptset(phdl, pc, &samesaved) < 0) {
		DPRINTFX("ERROR: couldn't restore breakpoint");
		return (-1);
	}
	assert(samesaved == saved);

	return (0);
}