[Bug breakpoints/27151] Step will skip subsequent statements for malloc functions

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=27151

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-01-06
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
I managed to reproduce this on ubuntu 20.

Configurations:
- gcc-10, system gdb,
- gcc-10, gdb build from current trunk.

The problem goes away when small.c is build with fcf-protection=none.

I tried to reproduce this on my usual setup, openSUSE Leap 15.2, by forcing
fcf-protection=full.  Didn't reproduce.

Copied Leap executable to ubuntu, and tried using gdb there.  Didn't reproduce.

Then copied ubuntu executable to Leap.  Reproduced.

So, sofar this seems specific to the ubuntu executable.

The two executables have similar line info and insns for main.

There is a difference in the plt.

For leap, we have:
...
00000000000005f0 <malloc@plt>:
 5f0:   ff 25 32 0a 20 00       jmpq   *0x200a32(%rip) \
          # 201028 <malloc@GLIBC_2.2.5>
 5f6:   68 02 00 00 00          pushq  $0x2
 5fb:   e9 c0 ff ff ff          jmpq   5c0 <.plt>
...

For ubuntu, we have:
...
0000000000001090 <malloc@plt>:
    1090:       f3 0f 1e fa             endbr64
    1094:       f2 ff 25 35 2f 00 00    bnd jmpq *0x2f35(%rip) \
                  # 3fd0 <malloc@GLIBC_2.2.5>
    109b:       0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
...

Using "set debug infrun 1", with leap we have:
...
[infrun] handle_signal_stop: stop_pc=0x5555555545f0
[infrun] process_event_stop_test: stepped into dynsym resolve code
...
where:
...
(gdb) info sym 0x5555555545f0        
malloc@plt in section .plt of /home/vries/gdb_versions/devel/a.leap.out
...

But with ubuntu we have:
...
[infrun] handle_signal_stop: stop_pc=0x555555555090
[infrun] process_event_stop_test: stepped into subroutine
[infrun] insert_step_resume_breakpoint_at_sal_1: inserting step-resume
breakpoint at 0x7ffff7df0710
...
where:
...
(gdb) info sym 0x555555555090
malloc@plt in section .plt.sec of /home/vries/gdb_versions/devel/a.out
...
and:
...
(gdb) info sym 0x7ffff7df0710
malloc in section .text of /lib64/ld-linux-x86-64.so.2
...
Looking for the "stepped into dynsym resolve code" in the gdb sources, we find
in_solib_dynsym_resolve_code, which returns false with the ubuntu exec, and
true with the leap exec.

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