Backtrace inside Signal Handler - c++

Question

I'm trying to following the code from this post to have signal handlers print a backtrace on errors such as floating point and segmentation faults. I'm using seg fault signals as a starting point. Here is the code:
#include <cstdlib> //for exit()
#include <signal.h> //signal handling
#include <execinfo.h> //backtrace, backtrace_symbols and backtrace_fd
#include <iostream>
#include <string.h>
#include <stdio.h>
#define TRACE_MSG fprintf(stderr, "TRACE at: %s() [%s:%d]\n", \
__FUNCTION__, __FILE__, __LINE__)
void show_stackframe()
{
void *trace[1024];
char **messages = (char **) NULL;
int i, trace_size = 0;
TRACE_MSG;
trace_size = backtrace(trace, 1024); // segfault here???
// More code here to print backtrace, but not needed at the moment..
TRACE_MSG;
}
void sigSegvHandler( int signum, siginfo_t* info, void* arg )
{
TRACE_MSG;
show_stackframe();
return;
}
double func_b()
{
show_stackframe(); // Show that backtrace works without being
// called inside sighandler.
TRACE_MSG;
int int_a[5];
int_a[0] = 4;
int_a[11] = 10; // cause a segfault on purpose to see
// how the signal handling performs.
return 1.1;
}
int main()
{
// Examine and change the seg fault signal
struct sigaction segvAction; // File: /usr/include/bits/sigaction.h
// Initialize segvAction struct to all zeros for initialiation
memset( &segvAction, 0, sizeof( segvAction ) );
segvAction.sa_sigaction = sigSegvHandler;
segvAction.sa_flags = SA_SIGINFO; //Invoke signal catching function with 3 arguments instead of 1
// Set the action for the SIGSEGV signal
sigaction( SIGSEGV, &segvAction, NULL );
func_b(); // Produce a SIGSEGV error
}
I am compiling using:
g++ -rdynamic testprogram.cpp -o testprogram
I receive the following output from the program:
TRACE at: show_stackframe() [stackoverflow.cpp:15]
TRACE at: show_stackframe() [stackoverflow.cpp:17]
TRACE at: func_b() [stackoverflow.cpp:33]
TRACE at: sigSegvHandler() [stackoverflow.cpp:22]
TRACE at: show_stackframe() [stackoverflow.cpp:15]
Segmentation fault
My question is why does show_stackframe() cause a segmentation fault inside of sigaction but works fine when not inside of the sigaction handler? I obviously seem to be setting up the signal handler/action incorrect but I haven't been able to find it all day. GDB doesn't seem to be any help in this case.

Answer 1

As stated here, the backtrace function is AS-Unsafe, which means it is unsafe to call from an asynchronous signal handler. Doing so invokes undefined behavior.