/* $NetBSD: backtrace.c,v 1.9 2025/01/23 12:08:12 christos Exp $ */
/*-
* Copyright (c) 2012 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Christos Zoulas.
*
* 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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>
__RCSID("$NetBSD: backtrace.c,v 1.9 2025/01/23 12:08:12 christos Exp $");
#include <sys/param.h>
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdarg.h>
#include <stdint.h>
#include <stddef.h>
#include <unistd.h>
#include <fcntl.h>
#include <dlfcn.h>
#include <elf.h>
#include "execinfo.h"
#include "symbol.h"
#include "symtab.h"
#ifdef __linux__
#define SELF "/proc/self/exe"
#else
#include <sys/sysctl.h>
#define SELF "/proc/curproc/file"
#endif
static int self_fd = -1;
static int
open_self(int flags)
{
const char *pathname = SELF;
#ifdef KERN_PROC_PATHNAME
static const int name[] = {
CTL_KERN, KERN_PROC_ARGS, -1, KERN_PROC_PATHNAME,
};
char path[MAXPATHLEN];
size_t len;
len = sizeof(path);
if (sysctl(name, __arraycount(name), path, &len, NULL, 0) != -1)
pathname = path;
#endif
return open(pathname, flags);
}
int
backtrace_sandbox_init(void)
{
if (self_fd == -1)
self_fd = open_self(O_RDONLY);
return self_fd >= 0 ? 0 : -1;
}
void
backtrace_sandbox_fini(void)
{
assert(self_fd >= 0);
close(self_fd);
self_fd = -1;
}
static int __printflike(4, 5)
rasprintf(char **buf, size_t *bufsiz, size_t offs, const char *fmt, ...)
{
for (;;) {
size_t nbufsiz;
char *nbuf;
if (*buf && offs < *bufsiz) {
va_list ap;
int len;
va_start(ap, fmt);
len = vsnprintf(*buf + offs, *bufsiz - offs, fmt, ap);
va_end(ap);
if (len < 0 || (size_t)len + 1 < *bufsiz - offs)
return len;
nbufsiz = MAX(*bufsiz + 512, (size_t)len + 1);
} else
nbufsiz = MAX(offs, *bufsiz) + 512;
nbuf = realloc(*buf, nbufsiz);
if (nbuf == NULL)
return -1;
*buf = nbuf;
*bufsiz = nbufsiz;
}
}
/*
* format specifiers:
* %a = address
* %n = symbol_name
* %d = symbol_address - address
* %D = if symbol_address == address "" else +%d
* %f = filename
*/
static ssize_t
format_string(char **buf, size_t *bufsiz, size_t offs, const char *fmt,
Dl_info *dli, const void *addr)
{
const uintptr_t symaddr = SYMBOL_CANONICALIZE(dli->dli_saddr);
ptrdiff_t diff = (const char *)addr - (const char *)symaddr;
size_t o = offs;
int len;
for (; *fmt; fmt++) {
if (*fmt != '%')
goto printone;
switch (*++fmt) {
case 'a':
len = rasprintf(buf, bufsiz, o, "%p", addr);
break;
case 'n':
len = rasprintf(buf, bufsiz, o, "%s", dli->dli_sname);
break;
case 'D':
if (diff)
len = rasprintf(buf, bufsiz, o, "+0x%tx", diff);
else
len = 0;
break;
case 'd':
len = rasprintf(buf, bufsiz, o, "0x%tx", diff);
break;
case 'f':
len = rasprintf(buf, bufsiz, o, "%s", dli->dli_fname);
break;
default:
printone:
len = rasprintf(buf, bufsiz, o, "%c", *fmt);
break;
}
if (len == -1)
return -1;
o += len;
}
return o - offs;
}
static ssize_t
format_address(symtab_t *st, char **buf, size_t *bufsiz, size_t offs,
const char *fmt, const void *addr)
{
Dl_info dli;
memset(&dli, 0, sizeof(dli));
(void)dladdr(addr, &dli);
if (st)
symtab_find(st, addr, &dli);
if (dli.dli_sname == NULL)
dli.dli_sname = "???";
if (dli.dli_fname == NULL)
dli.dli_fname = "???";
if (dli.dli_saddr == NULL)
dli.dli_saddr = (void *)(intptr_t)addr;
return format_string(buf, bufsiz, offs, fmt, &dli, addr);
}
char **
backtrace_symbols_fmt(void *const *trace, size_t len, const char *fmt)
{
static const size_t slen = sizeof(char *) + 64; /* estimate */
char *ptr;
symtab_t *st;
int fd = self_fd;
if (fd != -1 || (fd = open_self(O_RDONLY)) != -1)
st = symtab_create(fd, -1, STT_FUNC);
else
st = NULL;
if ((ptr = calloc(len, slen)) == NULL)
goto out;
size_t psize = len * slen;
size_t offs = len * sizeof(char *);
/* We store only offsets in the first pass because of realloc */
for (size_t i = 0; i < len; i++) {
ssize_t x;
((char **)(void *)ptr)[i] = (void *)offs;
x = format_address(st, &ptr, &psize, offs, fmt, trace[i]);
if (x == -1) {
free(ptr);
ptr = NULL;
goto out;
}
offs += x;
ptr[offs++] = '\0';
assert(offs < psize);
}
/* Change offsets to pointers */
for (size_t j = 0; j < len; j++)
((char **)(void *)ptr)[j] += (intptr_t)ptr;
out:
symtab_destroy(st);
if (fd != -1 && fd != self_fd)
(void)close(fd);
return (void *)ptr;
}
int
backtrace_symbols_fd_fmt(void *const *trace, size_t len, int fd,
const char *fmt)
{
char **s = backtrace_symbols_fmt(trace, len, fmt);
if (s == NULL)
return -1;
for (size_t i = 0; i < len; i++)
if (dprintf(fd, "%s\n", s[i]) < 0)
break;
free(s);
return 0;
}
static const char fmt[] = "%a <%n%D> at %f";
char **
backtrace_symbols(void *const *trace, size_t len)
{
return backtrace_symbols_fmt(trace, len, fmt);
}
int
backtrace_symbols_fd(void *const *trace, size_t len, int fd)
{
return backtrace_symbols_fd_fmt(trace, len, fd, fmt);
}
