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* [Bug c/111896] New: call with wrong stack alignment
@ 2023-10-20 14:29 lukas.graetz@tu-darmstadt.de
  2023-10-20 15:33 ` [Bug target/111896] " pinskia at gcc dot gnu.org
                   ` (4 more replies)
  0 siblings, 5 replies; 6+ messages in thread
From: lukas.graetz@tu-darmstadt.de @ 2023-10-20 14:29 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111896

            Bug ID: 111896
           Summary: call with wrong stack alignment
           Product: gcc
           Version: 9.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lukas.graetz@tu-darmstadt.de
  Target Milestone: ---

Created attachment 56157
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56157&action=edit
ccnhCTdD.i.tmp.i

For some reason, I manged to get a SEGV when running a program. I spent time
debugging it, and found out that the problem was when executing:

movaps %xmm0,0x40(%rsp)

It took me some time, but I realized the SEGV was caused by the rsp pointer 8
bytes off. It should be aligned to 16 bytes. So wrong alignment. I also found
out where the misalignment happend.

See the attached file. dlist_free_original() is calling freeit(). This is
compiled as dlist_free_original.constprop.0 calling do_line() as follows:

dlist_free_original.constprop.0:
...
        pushq   %rbp
...
        pushq   %rbx
...
        call    do_line

So the stack is misaligned when the call happens. It might be because do_line()
is written in inline asm with __attribute__((naked)).

Starting with gcc 11.3, there seems to be an extra "sub rsp,8" which seems to
solve this. But I was using gcc 9.4.0 (shipped with ubuntu 20.04) on amd64
linux. A quick check on godbolt showed me that misalignment still happen in gcc
11.2. So I am unsure if this is still relevant but I am reporting just in case.

gcc -O3 -c -S ccnhCTdD.i.tmp.i -o tmp.s

If you need the full executable or anything else, ask me.

Background:

I wanted to have a way to record which functions where called through a
pointer. For that, I created a wrapper for every function, renaming the
original function to ..._original. I also created a macro renaming direct calls
to _original so that only calls through a pointer were left. The wrapper
functions are doing their logging (it takes only a few instructions) and then
sibcall to the respective original function. A wrapper for vararg functions
seemed to be only possible using asm, so I used asm. Since the other functions
might be static, I had to do inline asm with attribute naked.

^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2023-10-20 16:35 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-10-20 14:29 [Bug c/111896] New: call with wrong stack alignment lukas.graetz@tu-darmstadt.de
2023-10-20 15:33 ` [Bug target/111896] " pinskia at gcc dot gnu.org
2023-10-20 16:02 ` lukas.graetz@tu-darmstadt.de
2023-10-20 16:31 ` pinskia at gcc dot gnu.org
2023-10-20 16:34 ` pinskia at gcc dot gnu.org
2023-10-20 16:35 ` lukas.graetz@tu-darmstadt.de

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