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From: "josopait at goopax dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libbacktrace/112322] New: std::stacktrace fails
Date: Tue, 31 Oct 2023 19:58:50 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: libbacktrace
X-Bugzilla-Version: 12.3.1
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X-Bugzilla-Who: josopait at goopax dot com
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112322

            Bug ID: 112322
           Summary: std::stacktrace fails
           Product: gcc
           Version: 12.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libbacktrace
          Assignee: unassigned at gcc dot gnu.org
          Reporter: josopait at goopax dot com
                CC: ian at gcc dot gnu.org
  Target Milestone: ---

I installed gcc on gentoo linux:

EXTRA_ECONF=3D"--enable-libstdcxx-backtrace=3Dyes" emerge gcc

and compiled the following program:



#include <iostream>
#include <stacktrace>

int main()
{
  std::cout << std::stacktrace::current() << std::endl;
}

$ g++-13 -g -std=3Dc++23 a.cpp -o a  -lstdc++_libbacktrace



When compiled with GCC 13 or GCC 14, the program output is weird:

$ ./a=20
   0#      at :32764
   1#      at :32764
   2#      at :32764
   3#      at :32764
   4#=20

The number 32764 changes randomly between program calls, in the range 32764=
 ..
32767.


When compiled with GCC 12, the program crashes with a segmentation fault:

(gdb) bt
#0  0x0000000000000000 in ?? ()
#1  0x000055555555ad41 in elf_nodebug (state=3D<optimized out>, pc=3D<optim=
ized
out>, callback=3D<optimized out>, data=3D<optimized out>, error_callback=3D=
<optimized
out>) at elf.c:585
#2  elf_nodebug (state=3D<optimized out>, pc=3D<optimized out>, callback=3D=
<optimized
out>, error_callback=3D<optimized out>, data=3D<optimized out>) at elf.c:565
#3  0x0000555555557c0f in std::stacktrace_entry::_M_get_info
(this=3D0x55555557e2b0, __desc=3D0x7fffffffdb60, __file=3D0x7fffffffdb80,
__line=3D0x7fffffffdb5c) at
/usr/lib/gcc/x86_64-pc-linux-gnu/12/include/g++-v12/stacktrace:191
#4  0x0000555555557db2 in std::operator<< (__os=3D..., __f=3D...) at
/usr/lib/gcc/x86_64-pc-linux-gnu/12/include/g++-v12/stacktrace:722
#5  0x00005555555585ce in std::operator<<
<std::allocator<std::stacktrace_entry> > (__os=3D..., __st=3D...) at
/usr/lib/gcc/x86_64-pc-linux-gnu/12/include/g++-v12/stacktrace:737
#6  0x0000555555557492 in main () at a.cpp:8

Here, parameter `state` of function elf_nodebug points to:
(gdb) p *__state
$10 =3D {filename =3D 0x0, threaded =3D 1, lock =3D 0x0, fileline_fn =3D 0x=
55555555a5f0
<elf_nodebug>, fileline_data =3D 0x0, syminfo_fn =3D 0x55555555a5d0 <elf_no=
syms>,
syminfo_data =3D 0x0, fileline_initialization_failed =3D 0, lock_alloc =3D =
0,
freelist =3D 0x7ffff7fc4048}

and error_callback is NULL, which causes the segmentation fault.=