一．用途：
主要用於程序異常退出時尋找錯誤原因
二．功能：
回溯堆棧，簡單的說就是可以列出當前函數調用關系
三．原理：
1． 通過對當前堆棧的分析，找到其上層函數在棧中的幀地址，再分析上層函數的堆棧，再找再上層的幀地址……一直找到最頂層為止，幀地址指的是一塊：在棧上存放局部變量，上層返回地址，及寄存器值的空間。
2． 由於不同處理器堆棧方式不同，此功能的具體實現是編譯器的內建函數__buildin_frame_address及__buildin_return_address中，它涉及工具glibc和gcc, 如果編譯器不支持此函數，也可自己實現此函數，舉例中有arm上的實現
四．方法：
在程序中加入backtrace及相關函數調用
五．舉例：
1． 一般backtrace的實現
i. 程序
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <execinfo.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#define PRINT_DEBUG
static void print_reason(int sig, siginfo_t * info, void *secret)
{
void *array[10];
size_t size;
#ifdef PRINT_DEBUG
char **strings;
size_t i;
size = backtrace(array, 10);
strings = backtrace_symbols(array, size);
printf("Obtained %zd stack frames.\n", size);
for (i = 0; i < size; i++)
printf("%s\n", strings[i]);
free(strings);
#else
int fd = open("err.log", O_CREAT | O_WRONLY);
size = backtrace(array, 10);
backtrace_symbols_fd(array, size, fd);
close(fd);
#endif
exit(0);
}
void die()
{
char *test1;
char *test2;
char *test3;
char *test4 = NULL;
strcpy(test4, "ab");
}
void test1()
{
die();
}
int main(int argc, char **argv)
{
struct sigaction myAction;
myAction.sa_sigaction = print_reason;
sigemptyset(&myAction.sa_mask);
myAction.sa_flags = SA_RESTART | SA_SIGINFO;
sigaction(SIGSEGV, &myAction, NULL);
sigaction(SIGUSR1, &myAction, NULL);
sigaction(SIGFPE, &myAction, NULL);
sigaction(SIGILL, &myAction, NULL);
sigaction(SIGBUS, &myAction, NULL);
sigaction(SIGABRT, &myAction, NULL);
sigaction(SIGSYS, &myAction, NULL);
test1();
}
ii. 編譯參數
gcc main.c -o test -g -rdynamic
2． 根據不同的處理器自已實現backtrace
i. arm的backtrace函數實現
static int backtrace_xy(void **BUFFER, int SIZE)
{
volatile int n = 0;
volatile int *p;
volatile int *q;
volatile int ebp1;
volatile int eip1;
volatile int i = 0;
p = &n;
ebp1 = p[4];
eip1 = p[6];
fprintf(stderr, "======================= backtrace_xy addr: 0x%0x, param1: 0x%0x, param2: 0x%0x\n",
backtrace_xy, &BUFFER, &SIZE);
fprintf(stderr, "n addr is 0x%0x\n", &n);
fprintf(stderr, "p addr is 0x%0x\n", &p);
for (i = 0; i < SIZE; i++)
{
fprintf(stderr, "ebp1 is 0x%0x, eip1 is 0x%0x\n", ebp1, eip1);
BUFFER[i] = (void *)eip1;
p = (int*)ebp1;
q = p - 5;
eip1 = q[5];
ebp1 = q[2];
if (ebp1 == 0 || eip1 == 0)
break;
}
fprintf(stderr, "total level: %d\n", i);
return i;
}
六．舉例2：
/*main.c*/
#include "sigsegv.h"
#include <string.h>
int die() {
char *err = NULL;
strcpy(err, "gonner");
return 0;
}
int main() {
return die();
}
/*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>
#define NO_CPP_DEMANGLE
#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"
#endif
static 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, info->si_codes[si_code]);
fprintf(stderr, "info->si_addr = %p\n", info->si_addr);
for(i = 0; i < 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_INIT
static void __attribute((constructor)) init(void)
{
setup_sigsegv();
}
#endif
/*sigsegv.h*/
#ifndef __sigsegv_h__
#define __sigsegv_h__
#ifdef __cplusplus
extern "C" {
#endif
int setup_sigsegv();
#ifdef __cplusplus
}
#endif
#endif /* __sigsegv_h__ */
編譯時需要加入-rdynamic -ldl –ggdb
void
handle_signal_error(int rec_signal,siginfo_t* signal_info,void* context)
{
NE_Info* __attribute__ ((unused)) ne_info = NULL;
struct sigaction action;
FILE* file;
void* backtr[NUMBER_OF_BACKTRACE];
cpal_uns32 __attribute__ ((unused)) i = 0;
cpal_uns32 backtr_size = 0;
ucontext_t *u_context;
time_t seconds_time;
struct tm* time_struct;
cpal_si32 ret_t;
char filename[SIZE_OF_FILENAME];
if(g_handler_running)
return;
g_handler_running = CPAL_TRUE;
ret_t = time(&seconds_time);
if(ret_t != - 1)
{
time_struct = gmtime(&seconds_time);
snprintf(filename,SIZE_OF_FILENAME,"%s%d%d%d-%d%d%d-%s",BACKTRACE_FILE_PATH,time_struct->tm_mon,time_struct->tm_mday,
(time_struct->tm_year-100)+2000,time_struct->tm_hour,time_struct->tm_min,time_struct->tm_sec,BACKTRACE_FILE);
}
else
{
snprintf(filename,SIZE_OF_FILENAME,"%s",BACKTRACE_FILE);
}
file = fopen(filename,"w");
if(file == NULL)
{
return;
}
if(signal_info == NULL)
{
return;
}
if(context == NULL)
{
return;
}
u_context = (ucontext_t*)context;
/*Restore the default action for this signal and re-raise it, so that the default action occurs. */
action.sa_sigaction = SIG_DFL;
sigemptyset(&action.sa_mask);
action.sa_flags = SA_RESTART;
sigaction(rec_signal,&action,NULL);
/* Print out the backtrace. */
backtr_size = backtrace(backtr,20);
/* The backtrace points to sigaction in libc, not to where the signal was actually raised.
This overwrites the sigaction with where the signal was sent, so we can resolve the sender. */
#if __WORDSIZE == 64
backtr[1] = (void*)u_context->uc_mcontext.gregs[REG_RIP];
#else
backtr[1] = (void*)u_context->uc_mcontext.gregs[REG_EIP];
#endif //__WORDSIZE
backtrace_symbols_fd(backtr,backtr_size,fileno(file));
fprintf(file,"Backtrace is above.\nFatal signal %d received.\n",rec_signal);
#if __WORDSIZE == 64
fprintf(file,"Signal received at address %p from 0x%08x.\n",signal_info->si_addr,
u_context->uc_mcontext.gregs[REG_RIP]);
#else
fprintf(file,"Signal received at address %p from 0x%08x.\n",signal_info->si_addr,
u_context->uc_mcontext.gregs[REG_EIP]);
#endif //__WORDSIZE
#if CPAL_LM_DEBUG
/* Print all NE_Infos */
for(; i < MAX_NO_OF_CONNS; i++)
{
ne_info = g_ne_hash_tab[i];
while(ne_info != NULL)
{
ne_info = ne_info->next_ne;
}
}
#endif
fflush(file);
fclose(file);
sleep (50); /* Sleep for 50 seconds */
g_handler_running = *_FALSE;
raise(rec_signal);
}
