[Bug libc/24401] backtrace_symbols not accurate with optimisation -O1

[jg at jguk dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=24401

--- Comment #3 from Jonny Grant <jg at jguk dot org> ---
(In reply to Andreas Schwab from comment #2)
> What is the issue exactly?

Hi!

I don't know the cause. But GDB is accurate, backtrace_symbols() is *not*
accurate.  It shows basic_string.h:176

backtrace_symbols() for some reason leads to:
basic_string.h:176 is _M_data() in that STL file.

Modified SEGV at end of print_trace. I'll attach this test case.

$ ./exception4
Unhandled C++ exception: [vector::_M_range_check: __n (which is 0) >=
this->size() (which is 0)]

Backtrace:
[0]: ./exception4(+0x11da) [0x55cfa17411da]
print_trace()
exception4.cpp:20
[1]: ./exception4(+0x15c1) [0x55cfa17415c1]
test()
basic_string.h:176
[2]: ./exception4(+0x1627) [0x55cfa1741627]
main
exception4.cpp:94
[3]: /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7) [0x7fe576d0cb97]
??
??:0
[4]: ./exception4(+0x10ca) [0x55cfa17410ca]
_start
??:?
Segmentation fault (core dumped)
$
$ gdb -c core exception4
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Reading symbols from exception4...done.
[New LWP 3468]
Core was generated by `./exception4'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  __GI_raise (sig=<optimised out>) at ../sysdeps/unix/sysv/linux/raise.c:51
51      ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) bt
#0  __GI_raise (sig=<optimised out>) at ../sysdeps/unix/sysv/linux/raise.c:51
#1  0x000055cfa1741508 in print_trace () at exception4.cpp:73
#2  0x000055cfa17415c1 in test () at exception4.cpp:86
#3  0x000055cfa1741627 in main () at exception4.cpp:93

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