xref: /freebsd/lib/libproc/proc_bkpt.c (revision 8eb20f364fe0e4a0cbbbce6b8456a75324ae95d8)

/*
 * 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/cdefs.h>
__FBSDID("$FreeBSD$");

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

#include <assert.h>
#include <err.h>
#include <stdio.h>
#include <errno.h>
#include "_libproc.h"

#if defined(__i386__) || defined(__amd64__)
#define BREAKPOINT_INSTR	0xcc	/* int 0x3 */
#define	BREAKPOINT_INSTR_SZ	1
#else
#error "Add support for your architecture"
#endif

int
proc_bkptset(struct proc_handle *phdl, uintptr_t address,
    unsigned long *saved)
{
	struct ptrace_io_desc piod;
	unsigned long paddr, caddr;

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

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

	return (0);
}

int
proc_bkptdel(struct proc_handle *phdl, uintptr_t address,
    unsigned long saved)
{
	struct ptrace_io_desc piod;
	unsigned long paddr, caddr;

	if (phdl->status == PS_DEAD || phdl->status == PS_UNDEAD ||
	    phdl->status == PS_IDLE) {
		errno = ENOENT;
		return (-1);
	}
	DPRINTF("removing breakpoint at 0x%lx\n", address);
	/*
	 * Overwrite the breakpoint instruction that we setup previously.
	 */
	caddr = address;
	paddr = saved;
	piod.piod_op = PIOD_WRITE_I;
	piod.piod_offs = (void *)caddr;
	piod.piod_addr = &paddr;
	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%" PRIuPTR,
		    address);
		return (-1);
	}

	return (0);
}

/*
 * Decrement pc so that we delete the breakpoint at the correct
 * address, i.e. at the BREAKPOINT_INSTR address.
 */
void
proc_bkptregadj(unsigned long *pc)
{
	*pc = *pc - BREAKPOINT_INSTR_SZ;
}

/*
 * 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) {
		warn("ERROR: couldn't get PC register");
		return (-1);
	}
	proc_bkptregadj(&pc);
	if (proc_bkptdel(phdl, pc, saved) < 0) {
		warn("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) {
		warn("ERROR: ptrace step failed");
		return (-1);
	}
	status = proc_wstatus(phdl);
	if (!WIFSTOPPED(status)) {
		warn("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) {
		warn("ERROR: couldn't restore breakpoint");
		return (-1);
	}
	assert(samesaved == saved);

	return (0);
}