https://bugs.llvm.org/show_bug.cgi?id=47405
Bug ID: 47405
Summary: __attribute__((force_align_arg_pointer)) ignored by
non-virtual thunk on x86
Product: clang
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: LLVM Codegen
Assignee: unassignedclangb...@nondot.org
Reporter: shadow_m...@mail.ru
CC: llvm-bugs@lists.llvm.org, neeil...@live.com,
richard-l...@metafoo.co.uk
Compiler generates incorrect non-virtual thunk in case of multiple inheritance.
It seems that clang ignores __attribute__((force_align_arg_pointer)) for thunk
and accepts it only for original function.
GCC (at least 7.3.0) handles the alignment correctly for original function and
for thunk.
As workaround we use an option -mstackrealign for clang.
But it causes unnecessary alternative prologue/epilogue for functions without
problematic thunks.
Minimal test case (https://godbolt.org/z/a847vd):
Options: -target i386-pc-linux-gnu -O2
#include <stdio.h>
#include <memory.h>
struct A
{
virtual void TestA() { printf("TestA\n"); }
};
struct B
{
//__attribute__((force_align_arg_pointer))
virtual void TestB() { printf("TestB\n"); }
};
struct C : public A, public B
{
__attribute__((force_align_arg_pointer))
virtual void TestB() { printf("TestB by C\n"); }
virtual void TestC() { printf("TestC\n"); }
};
----------------------------------------------------------
CLANG 8, 9, 10
C::TestB(): # @C::TestB()
push ebp
mov ebp, esp
and esp, -16 <--- Stack alignment
sub esp, 16
mov dword ptr [esp], offset .Lstr.5
call puts
mov esp, ebp
pop ebp
ret
non-virtual thunk to C::TestB(): # @non-virtual thunk to C::TestB()
sub esp, 12 <--- No Stack alignment
mov dword ptr [esp], offset .Lstr.5
call puts
add esp, 12
ret
-----------------------------------------
GCC 7.3.0:
C::TestB():
lea ecx, [esp+4]
and esp, -16
push DWORD PTR [ecx-4]
push ebp
mov ebp, esp
push ecx
sub esp, 16
push OFFSET FLAT:.LC2
call puts
mov ecx, DWORD PTR [ebp-4]
add esp, 16
leave
lea esp, [ecx-4]
ret
non-virtual thunk to C::TestB():
lea ecx, [esp+4]
and esp, -16
push DWORD PTR [ecx-4]
push ebp
mov ebp, esp
push ecx
sub esp, 16
push OFFSET FLAT:.LC2
call puts
mov ecx, DWORD PTR [ebp-4]
add esp, 16
leave
lea esp, [ecx-4]
ret
--
You are receiving this mail because:
You are on the CC list for the bug._______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
