[Bug target/56807] mingw32: Conflict between stack realignment and stack probe destroys function argument in EAX

[BugMaster at narod dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56807

Anton Mitrofanov  changed:

   What|Removed |Added

 CC||BugMaster at narod dot ru

--- Comment #18 from Anton Mitrofanov  ---
This patch is ok for mingw32 target but may produce incorrect code for x86_64
linux target in case of saving/restoring both rax and r10. In that case during
restoring of rax register (in "if (r10_live && eax_live)" path of
http://gcc.gnu.org/viewcvs/gcc/trunk/gcc/config/i386/i386.c?r1=205860&r2=205859&pathrev=205860)
we will make move from incorrect address [rsp + allocate - UNITS_PER_WORD]
while the saved value will be at address [rsp + allocate + UNITS_PER_WORD].
Here is possible code that can be generated (by looking at current gcc source
code):

// suppose rsp == 1000 here
push rax // rsp == 992 ; [992] == rax
push r10 // rsp == 984 ; [984] == r10
mov rax, 400 // where 400 is allocate value
call allocate_stack
sub rsp, rax // rax == 400 so rsp == 584
mov r10, [rsp + 400] // 584 + 400 == 984 ; r10 = [984]
mov rax, [rsp + 400 - 8] // 584 + 400 - 8 == 976 ; rax = [976] <- WRONG

Instead the last instruction should be

mov rax, [rsp + 400 + 8] // 584 + 400 + 8 == 992 ; rax = [992]

Sorry, I can't write test case to trigger this code path so I will leave this
comment here and not create new bug report (if you want you can move it to new
bug report).

[Bug target/56807] mingw32: Conflict between stack realignment and stack probe destroys function argument in EAX

[BugMaster at narod dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56807

--- Comment #20 from Anton Mitrofanov  ---
I was talking about:

 if (r10_live && eax_live)
{
  t = plus_constant (Pmode, stack_pointer_rtx, allocate);
  emit_move_insn (gen_rtx_REG (word_mode, R10_REG),
  gen_frame_mem (word_mode, t));
  t = plus_constant (Pmode, stack_pointer_rtx,
 allocate - UNITS_PER_WORD);
  emit_move_insn (gen_rtx_REG (word_mode, AX_REG),
  gen_frame_mem (word_mode, t));
}

And especially:
  t = plus_constant (Pmode, stack_pointer_rtx,
 allocate - UNITS_PER_WORD);

[Bug target/56807] mingw32: Conflict between stack realignment and stack probe destroys function argument in EAX

[BugMaster at narod dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56807

--- Comment #21 from Anton Mitrofanov  ---
It should be:
  t = plus_constant (Pmode, stack_pointer_rtx,
 allocate + UNITS_PER_WORD);

[Bug target/56807] mingw32: Conflict between stack realignment and stack probe destroys function argument in EAX

[BugMaster at narod dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56807

--- Comment #23 from Anton Mitrofanov  ---

>Is it possible to write a test with eax_live == true and r10_live == true?
I am really dunno. As I said I can't write sample which will trigger it (that
is why it is only comment and not new bug report). But this code path exist so
probably someone suggested that it can be triggered (otherwise what for to
write it instead of some assert)?

>That piece of code is only trigged by -mstack-arg-probe, which is
specific to Windows
Can it really be used only for Windows target? I am not very good with gcc on
other targets so don't know if it have any effect on linux or anything other.