https://jackxiang.com/index.php zh-cn https://jackxiang.com/post// jack <xdy108@126.com> Sun, 04 Oct 2009 04:49:21 +0000 https://jackxiang.com/post//
sigsegv.h

#ifndef __sigsegv_h__#define __sigsegv_h__#ifdef __cplusplusextern "C" {#endif  int setup_sigsegv();#ifdef __cplusplus}#endif#endif /* __sigsegv_h__ */

sigsegv.c

#define _GNU_SOURCE#include <memory.h>#include <stdlib.h>#include <stdio.h>#include <signal.h>#include <ucontext.h>#include <dlfcn.h>#include <execinfo.h>#ifndef NO_CPP_DEMANGLE#include <cxxabi.h>#endif#if defined(REG_RIP)# define SIGSEGV_STACK_IA64# define REGFORMAT "%016lx"#elif defined(REG_EIP)# define SIGSEGV_STACK_X86# define REGFORMAT "%08x"#else# define SIGSEGV_STACK_GENERIC# define REGFORMAT "%x"#endifstatic void signal_segv(int signum, siginfo_t* info, void*ptr) {  static const char *si_codes[3] = {"", "SEGV_MAPERR", "SEGV_ACCERR"};  size_t i;  ucontext_t *ucontext = (ucontext_t*)ptr;#if defined(SIGSEGV_STACK_X86) || defined(SIGSEGV_STACK_IA64)  int f = 0;  Dl_info dlinfo;  void **bp = 0;  void *ip = 0;#else  void *bt[20];  char **strings;  size_t sz;#endif  fprintf(stderr, "Segmentation Fault!\n");  fprintf(stderr, "info.si_signo = %d\n", signum);  fprintf(stderr, "info.si_errno = %d\n", info->si_errno);  fprintf(stderr, "info.si_code  = %d (%s)\n", info->si_code, si_codes[info->si_code]);  fprintf(stderr, "info.si_addr  = %p\n", info->si_addr);  for(i = 0; i &lt; NGREG; i++)    fprintf(stderr, "reg[%02d]       = 0x" REGFORMAT "\n", i, ucontext->uc_mcontext.gregs[i]);#if defined(SIGSEGV_STACK_X86) || defined(SIGSEGV_STACK_IA64)# if defined(SIGSEGV_STACK_IA64)  ip = (void*)ucontext->uc_mcontext.gregs[REG_RIP];  bp = (void**)ucontext->uc_mcontext.gregs[REG_RBP];# elif defined(SIGSEGV_STACK_X86)  ip = (void*)ucontext->uc_mcontext.gregs[REG_EIP];  bp = (void**)ucontext->uc_mcontext.gregs[REG_EBP];# endif  fprintf(stderr, "Stack trace:\n");  while(bp && ip) {    if(!dladdr(ip, &dlinfo))      break;    const char *symname = dlinfo.dli_sname;#ifndef NO_CPP_DEMANGLE    int status;    char *tmp = __cxa_demangle(symname, NULL, 0, &status);    if(status == 0 && tmp)      symname = tmp;#endif    fprintf(stderr, "% 2d: %p <%s+%u> (%s)\n",            ++f,            ip,            symname,            (unsigned)(ip - dlinfo.dli_saddr),            dlinfo.dli_fname);#ifndef NO_CPP_DEMANGLE    if(tmp)      free(tmp);#endif    if(dlinfo.dli_sname && !strcmp(dlinfo.dli_sname, "main"))      break;    ip = bp[1];    bp = (void**)bp[0];  }#else  fprintf(stderr, "Stack trace (non-dedicated):\n");  sz = backtrace(bt, 20);  strings = backtrace_symbols(bt, sz);  for(i = 0; i < sz; ++i)    fprintf(stderr, "%s\n", strings[i]);#endif  fprintf(stderr, "End of stack trace\n");  exit (-1);}int setup_sigsegv() {  struct sigaction action;  memset(&action, 0, sizeof(action));  action.sa_sigaction = signal_segv;  action.sa_flags = SA_SIGINFO;  if(sigaction(SIGSEGV, &action, NULL) < 0) {    perror("sigaction");    return 0;  }  return 1;}#ifndef SIGSEGV_NO_AUTO_INITstatic void __attribute((constructor)) init(void) {  setup_sigsegv();}#endif

main.c

#include "sigsegv.h"#include <string.h>int die() {  char *err = NULL;  strcpy(err, "gonner");  return 0;}int main() {  return die();}

下面来编译上面的main.c程序看看将会产生什么样的信息呢，不过要注意的就是如果要在你的程序里引用sigsegv.h、sigsegv.c得到堆栈信息的话记得加上-rdynamic -ldl参数。

/data/codes/c/test/backtraces $ gcc -o test -rdynamic -ldl -ggdb -g sigsegv.c main.c/data/codes/c/test/backtraces $ ./testSegmentation Fault!info.si_signo = 11info.si_errno = 0info.si_code  = 1 (SEGV_MAPERR)info.si_addr  = (nil)reg[00]       = 0x00000033reg[01]       = 0x00000000reg[02]       = 0xc010007breg[03]       = 0x0000007breg[04]       = 0x00000000reg[05]       = 0xb7fc8ca0reg[06]       = 0xbff04c2creg[07]       = 0xbff04c1creg[08]       = 0xb7f8cff4reg[09]       = 0x00000001reg[10]       = 0xbff04c50reg[11]       = 0x00000000reg[12]       = 0x0000000ereg[13]       = 0x00000006reg[14]       = 0x080489ecreg[15]       = 0x00000073reg[16]       = 0x00010282reg[17]       = 0xbff04c1creg[18]       = 0x0000007bStack trace: 1: 0x80489ec <die+16> (/data/codes/c/test/backtraces/test) 2: 0x8048a16 <main+19> (/data/codes/c/test/backtraces/test)End of stack trace/data/codes/c/test/backtraces $

下面用gdb来看看出错的地方左右的代码：

/data/codes/c/test/backtraces $ gdb ./testgdb> disassemble die+16Dump of assembler code for function die:0x080489dc <die+0>:     push   %ebp0x080489dd <die+1>:     mov    %esp,%ebp0x080489df <die+3>:     sub    $0x10,%esp0x080489e2 <die+6>:     movl   $0x0,0xfffffffc(%ebp)0x080489e9 <die+13>:    mov    0xfffffffc(%ebp),%eax0x080489ec <die+16>:    movl   $0x6e6e6f67,(%eax)0x080489f2 <die+22>:    movw   $0x7265,0x4(%eax)0x080489f8 <die+28>:    movb   $0x0,0x6(%eax)0x080489fc <die+32>:    mov    $0x0,%eax0x08048a01 <die+37>:    leave  0x08048a02 <die+38>:    ret    End of assembler dump.gdb&gt;

也可以直接break *die+16进行调试，看看在出错之前的堆栈情况，那么下面我们再来看看代码问题到底出在什么地方了。

/data/codes/c/test/backtraces $ gdb ./testgdb> break *die+16Breakpoint 1 at 0x80489f2: file main.c, line 6.gdb&gt; list *die+160x80489f2 is in die (main.c:6).1       #include "sigsegv.h"2       #include <string.h>3       4       int die() {5         char *err = NULL;6         strcpy(err, "gonner");7         return 0;8       }9       10      int main() {gdb>

现在看看定位错误将会多么方便，上面的调试指令中list之前break不是必须的，只是让你可以看到break其实就已经指出了哪一行代码导致 Segmentation fault了。如果你要发布你的程序你一般会为了减少体积不会附带调试信息的(也就是不加-ggdb -g参数)，不过没关系，你一样可以得到上面stack-trace信息，然后你调试之前只要加上调试信息即可。 ]]> https://jackxiang.com/post//#blogcomment <user@domain.com> Thu, 01 Jan 1970 00:00:00 +0000 https://jackxiang.com/post//#blogcomment