[Bug libstdc++/46751] New: backtrace_symbols wrong when in unexpected_handler

[Bug libstdc++/46751] New: backtrace_symbols wrong when in unexpected_handler

[erik at cq2 dot nl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46751

           Summary: backtrace_symbols wrong when in unexpected_handler
           Product: gcc
           Version: 4.4.5
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: erik@cq2.nl


When in an std::unexpected_handler, backtrace_symbols returns a trace with
functions not even called at all.  

I noticed strange functions to appear on the trace, and missed functions that
should be there.

I reproduced it with the following minimal code:

#include <exception>
#include <execinfo.h>

extern "C" void my_unexpected_handler() {
        void* trace[100];
        int size = backtrace(trace, 100);
        backtrace_symbols_fd(trace, size, 2);
}

void throw_0() throw() {
        throw 0;
}

extern "C" void not_called_at_all_but_appearing_on_the_backtrace() { }

extern "C" int main(int, char*[]) {
        std::set_unexpected(my_unexpected_handler);
        throw_0();
        return 0;
}

I compile this with: g++ -g -rdynamic <filename>
It then produces:

./a.out(my_unexpected_handler+0x1f)[0x8048973]
/usr/lib/libstdc++.so.6(+0xbd465)[0xb7853465]
/usr/lib/libstdc++.so.6(__cxa_call_unexpected+0x45)[0xb78528b5]
./a.out(not_called_at_all_but_appearing_on_the_backtrace+0x0)[0x80489dc]
./a.out(main+0x1a)[0x80489fb]
/lib/i686/cmov/libc.so.6(__libc_start_main+0xe6)[0xb7621c76]
./a.out[0x80488c1]
terminate called after throwing an instance of 'int'
Aborted

As you can see, "not_called_at_all_but_appearing_on_the_backtrace" is not
called anywhere, but yet it is on the stack trace.

The function throw_0 however is missing.

I believe this is a bug.  If not, what is going on here?

Best regards
Erik Groeneveld

[Bug libstdc++/46751] backtrace_symbols wrong when in unexpected_handler

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46751

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2010-12-01 19:18:02 UTC ---
backtrace is part of libc and not GCC.

[Bug libstdc++/46751] backtrace_symbols wrong when in unexpected_handler

[erik at cq2 dot nl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46751

--- Comment #2 from Erik J Groeneveld <erik at cq2 dot nl> 2010-12-01 19:27:26 UTC ---
(In reply to comment #1)
> backtrace is part of libc and not GCC.

Thank you, I'll post it there too.

Could it also have to do something with exception handling code in the c++
runtime that calls unexpected_handler?  I think it somehow leaves the stack in
a state that backtrace does not expect. That still leaves open the question
where the bug is, if any.

[Bug middle-end/46751] backtrace_symbols wrong when in unexpected_handler

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46751

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
          Component|libstdc++                   |middle-end
         Resolution|                            |INVALID

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-02-04 00:25:04 UTC ---
The backtrace is mostly right.  The issue is that the function after
_Z7throw_0v is not_called_at_all_but_appearing_on_the_backtrace.  

The debugging info is correct.  The call return place is really
not_called_at_all_but_appearing_on_the_backtrace.