Bug#605611: libc: backtrace_symbols wrong when in unexpected_handler

["Erik J. Groeneveld" <erik@cq2.nl>]

Package: libc6
Version: 2.11.2-7
Severity: normal
File: libc
Tags: upstream


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


-- System Information:
Debian Release: squeeze/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: i386 (i686)

Kernel: Linux 2.6.32-5-686-bigmem (SMP w/2 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages libc6 depends on:
ii  libc-bin                      2.11.2-7   Embedded GNU C Library: Binaries
ii  libgcc1                       1:4.4.5-6  GCC support library

Versions of packages libc6 recommends:
ii  libc6-i686                    2.11.2-7   Embedded GNU C Library: Shared lib

Versions of packages libc6 suggests:
ii  debconf [debconf-2.0]         1.5.36     Debian configuration management sy
pn  glibc-doc                     <none>     (no description available)
ii  locales                       2.11.2-7   Embedded GNU C Library: National L

-- debconf information excluded