Re: [RFC PATCH v2 3/8] tools/nolibc: i386: Implement syscall with 6 arguments

Ammar Faizi
2022-03-22T13:37:12Z

On 3/22/22 8:34 PM, Willy Tarreau wrote:
>> I turned out GCC refuses to use "rm" if we compile without -fomit-frame-pointer
>> (e.g. without optimization / -O0). So I will still use "m" here.
>
> OK that's fine. then you can probably simplify it like this:
>
> long _arg6 = (long)(arg6); /* Might be in memory */ \
> \
> asm volatile ( \
> "pushl %%ebp\n\t" \
> "movl %[_arg6], %%ebp\n\t" \
> "int $0x80\n\t" \
> "popl %%ebp\n\t" \
> : "=a"(_ret) \
> : "r"(_num), "r"(_arg1), "r"(_arg2), "r"(_arg3), \
> "r"(_arg4),"r"(_arg5), [_arg6]"m"(_arg6) \
> : "memory", "cc" \
> ); \
>
> See ? no more push, no more addl, direct load from memory.

Uggh... I crafted the same code like you suggested before, but then
I realized it's buggy, it's buggy because %[_arg6] may live in N(%esp).

When you pushl %ebp, the %esp changes, N(%esp) no longer points to the
6-th argument.

--
Ammar Faizi