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: [email protected]
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.
