I'm writing here because original gcc seems unaffected (asm code
https://gcc.godbolt.org/ looks right).
I don't want to post it to bugtracker, because my English skills are strongly
limited and someone else can write better report, so if you want, feel free to
do this :)
Function with variable arguments causes compiler (C and C++) to emit bad code.
For ms_abi functions generated with LTO turned on program will crash and for
sysv_abi program will generate wrong results.
Compiler: g++ (x86_64-posix-seh, Built by MinGW-W64 project) 6.1.0
System: Windows 10 x64
Target: x86_64-w64-mingw32
Example code:
--------------------------------------------------------------------------------
#include <cstdarg>
#include <cstdint>
#include <cstdio>
//__attribute__((sysv_abi))
void f1(void** x, ...) {
va_list ap;
va_start(ap, x);
while (x != nullptr) {
*x = nullptr;
x = va_arg (ap, void**);
}
va_end(ap);
}
int main() {
void* ptrs[] = {
(void*)0x87654321,
(void*)0x01234567,
(void*)0xFFFFFFFF,
(void*)0xBADC0FFEE0DDF00D,
};
f1(&ptrs[0], &ptrs[1], &ptrs[2], &ptrs[3], nullptr);
printf("%p %p %p %p", ptrs[0], ptrs[1], ptrs[2], ptrs[3]);
return 0;
}
--------------------------------------------------------------------------------
Cmdline:
g++ test.cpp -o test.exe -flto
test
--------------------------------------------------------------------------------
Results:
PASS: ms_abi --> 0000000000000000 0000000000000000 0000000000000000
0000000000000000
FAIL: ms_abi + LTO --> SIGSEGV
FAIL: sysv_abi --> 0000000000000000 0000000001234567 00000000ffffffff
badc0ffee0ddf00d
FAIL: sysv_abi + LTO --> 0000000000000000 0000000001234567 0000000000000000
0000000000000000
------------------------------------------------------------------------------
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