https://bugs.llvm.org/show_bug.cgi?id=52181
Bug ID: 52181
Summary: Incorrect code generation when using regcall with
-fPIC
Product: clang
Version: 12.0
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: LLVM Codegen
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected]
So I have a simple example here for x86 (-m32) where a regular cdecl function
is trying to call a function using the regcall convention.
__attribute__((regcall)) void bar();
void foo()
{
bar();
}
When this is compiled with -fPIC, the required loading of ebx table offsets by
the caller is incorrectly omitted.
foo(): # @foo()
push ebp
mov ebp, esp
sub esp, 8
call __regcall3__bar()@PLT
add esp, 8
pop ebp
ret
arguments are -m32 -fPIC -target i386-linux-elf, this happens in both C & C++
when the same code is compiled in GCC 13 we get correct code:
foo():
push ebp
mov ebp, esp
push ebx
sub esp, 4
call __x86.get_pc_thunk.ax
add eax, OFFSET FLAT:_GLOBAL_OFFSET_TABLE_
mov ebx, eax
call bar()@PLT
nop
mov ebx, DWORD PTR -4[ebp]
leave
ret
__x86.get_pc_thunk.ax:
mov eax, DWORD PTR [esp]
ret
note the loading of ebx with the offset of the GOT
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