On 27/03/2019 21:34, Jonathan Wakely wrote:
On Wed, 27 Mar 2019 at 21:27, Jonny Grant wrote:
Hi!
Thank you for your reply and input.
Maybe GCC's "libbacktrace" module could be used?
I was wondering if -fsanitize=address would output a backtrace for the
C++ exception, but it doesn't seem to. Also it actually prevents the
core being dumped - that's probably not intended?
Compile without Sanitizer, and it does dump the core to a file at least!
$ export UBSAN_OPTIONS=print_stacktrace=1
This is a UBsan option.
// g++-8 -fsanitize=address -Wall -o exception exception.cpp
But you're not using UBsan.
#include <vector>
int main()
{
std::vector<int> v;
return v.at(0);
}
$ ./exception
terminate called after throwing an instance of 'std::out_of_range'
what(): vector::_M_range_check: __n (which is 0) >= this->size()
(which is 0)
Aborted
There's no undefined behaviour or memory corruption here, so it's not
surprising that UBsan and Asan don't print anything.
Ok I see, thank you for pointing this out.
I did wonder, as -fsanitize=address seems to inhibit the core dump that
is otherwise created by the abort() that appears to be called - is that
a known issue?
$ g++-8 -Wall -o exception exception.cpp
jonny@asus:~/code/crash$ ./exception
terminate called after throwing an instance of 'std::out_of_range'
what(): vector::_M_range_check: __n (which is 0) >= this->size()
(which is 0)
Aborted (core dumped)
$
Usually I just load the core dump into GDB to take a look at it.
If you want a stack trace for exceptions that terminate the process
then you could install a custom terminate handler which does that.
Libstdc++'s default terminate handler just prints the message above,
which includes the type of the exception and if it's a type derived
from std::exception, the what() string stored in it.
Yes, I'd love to have a stack trace for exceptions that terminate the
process. Do you know a simple example you can refer me to? I've looked
and there are people using boost::stacktrace::stacktrace() but I'd
rather not link to boost as a dependency.
It would be great if there was a glibc option to do this, or GCC could
insert it.
Otherwise we each need to insert our own stack tracers...
Found this:
https://www.gnu.org/software/libc/manual/html_node/Backtraces.html
I added this (attached) to a C++ exception handler, but there's no file
and line numbers. Other examples resort to calling addr2line! Seems a
bit over the top for us each to code our own stack tracer... Or reading
symbols etc. Am I asking too much for a general print_backtrace() in
libc or elsewhere ?
Cheers, Jonny
// g++-8 -Wall -g -o exception exception.cpp
#include <vector>
#include <iostream>
int main2();
#include <execinfo.h>
#include <stdio.h>
#include <stdlib.h>
/* Obtain a backtrace and print it to stdout.
https://www.gnu.org/software/libc/manual/html_node/Backtraces.html
*/
void
print_trace (void)
{
void *array[10];
size_t size;
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 ("symbols %s\n", strings[i]);
free (strings);
}
int main()
{
try
{
main2();
}
catch( const std::exception &e)
{
const std::string what(e.what());
std::cout << "Unhandled exception: [" << what << "]\n";
print_trace();
exit(0);
}
}
int main2()
{
std::vector<int> v;
return v.at(0);
}
