On a mips platform, I am trying to get Unwind work. Currently if I issue print_trace manually stack trace is correctly shown as below:
backtrace_helper 0x4b6958
backtrace_helper 0x4b6ab4
backtrace_helper 0x2ac2f628
Obtained 3 stack frames.
./v(print_trace+0x38) [0x4b6958]
./v(main+0x90) [0x4b6ab4]
/lib/libc.so.0(__uClibc_main+0x24c) [0x2ac2f628]
But when a SIGSEGV occurs, stack trace does not show correct function call sequence.
backtrace_helper 0x4b7a74
backtrace_helper 0x2ab9b84c
Obtained 2 stack frames.
./v(getLineIDByPhyIdx+0x3d8) [0x4b7a74]
/lib/libpthread.so.0(__new_sem_post+0x2c8) [0x2ab9b84c]
I am compiling with -g -fexceptions -rdynamic. Also I have seen How to generate a stacktrace when my gcc C++ app crashes in which 2nd answer mentiones about wrong address but when I set as he does but it only changes 2nd frame and rest is the same, code snippet is below:
caller_address = (void *) uc->uc_mcontext.gregs[30]; // Frame pointer (from wikipedia here)
fprintf(stderr, "signal %d (%s), address is %p from %p\n",
sig_num, strsignal(sig_num), info->si_addr,
(void *)caller_address);
size = backtrace(array, 50);
/* overwrite sigaction with caller's address */
array[1] = caller_address;
messages = backtrace_symbols(array, size);
Code:
int main(int argc, char *argv[]) {
registerSignalHandler(signalHandler);
print_trace();
{
// Seg Fault
int *p = NULL;
*p = 54;
}
}
void print_trace(void) {
void *array[10];
size_t size;
char **strings;
size_t i;
/* Get the address at the time the signal was raised from the EIP (x86) */
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);
}
static _Unwind_Reason_Code
backtrace_helper (struct _Unwind_Context *ctx, void *a)
{
struct trace_arg *arg = a;
assert (unwind_getip != NULL);
/* We are first called with address in the __backtrace function. Skip it. */
if (arg->cnt != -1) {
arg->array[arg->cnt] = (void *) unwind_getip (ctx);
printf("backtrace_helper %p \n", arg->array[arg->cnt]);
}
if (++arg->cnt == arg->size)
return _URC_END_OF_STACK;
return _URC_NO_REASON;
}
/*
* Perform stack unwinding by using the _Unwind_Backtrace.
*
* User application that wants to use backtrace needs to be
* compiled with -fexceptions option and -rdynamic to get full
* symbols printed.
*/
int backtrace (void **array, int size)
{
struct trace_arg arg = { .array = array, .size = size, .cnt = -1 };
if (unwind_backtrace == NULL)
backtrace_init();
if (size >= 1)
unwind_backtrace (backtrace_helper, &arg);
return arg.cnt != -1 ? arg.cnt : 0;
}
void signalHandler( int sig, siginfo_t* siginfo, void* notused)
{
/* Print out the signal info */
signalInfo(sig, siginfo);
switch (sig) {
case SIGSEGV:
{
print_trace();
abort();
}
}
}
