From: David Laight <[email protected]>
To: 'Ammar Faizi' <[email protected]>, Willy Tarreau <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>,
Alviro Iskandar Setiawan <[email protected]>,
Nugraha <[email protected]>,
"Linux Kernel Mailing List" <[email protected]>,
GNU/Weeb Mailing List <[email protected]>,
"[email protected]" <[email protected]>,
"[email protected]" <[email protected]>
Subject: RE: [RFC PATCH v1 3/6] tools/nolibc: i386: Implement syscall with 6 arguments
Date: Sun, 20 Mar 2022 18:22:35 +0000 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
From: Ammar Faizi
> Sent: 20 March 2022 15:04
> On 3/20/22 8:10 PM, David Laight wrote:
> > From: Ammar Faizi
> >> Sent: 20 March 2022 09:38
> >>
> >> In i386, the 6th argument of syscall goes in %ebp. However, both Clang
> >> and GCC cannot use %ebp in the clobber list and in the "r" constraint
> >> without using -fomit-frame-pointer. To make it always available for any
> >> kind of compilation, the below workaround is implemented.
> >>
> >> For clang (the Assembly statement can't clobber %ebp):
> >> 1) Save the %ebp value to the redzone area -4(%esp).
> >
> > i386 doesn't have a redzone.
> > If you get a signal it will trash -4(%sp)
>
> OK, I missed that one. Thanks for reviewing this.
>
...
> >
> > One possibility might be to do:
> > push arg6
> > push %ebp
> > mov %ebp, 4(%sp)
>
> Did you mean `mov 4(%esp), %ebp`?
>
> > int 0x80
> > pop %ebp
> > add %esp,4
>
> I think your solution is better than the xchg approach (with the 3rd line
> fixed). Will take this in for the next version.
It has to be said that although I've been writing x86 asm
for 40 years (and others for longer) I can never actually
remember the exact syntax or order of the operands!
Probably because it is randomly different between assemblers.
You want the 'memory read' instruction: 8b /r.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-03-20 18:22 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-20 9:37 [RFC PATCH v1 0/6] Add dynamic memory allocator support for nolibc Ammar Faizi
2022-03-20 9:37 ` [RFC PATCH v1 1/6] tools/nolibc: x86-64: Update System V ABI document link Ammar Faizi
2022-03-20 9:37 ` [RFC PATCH v1 2/6] tools/nolibc: Make the entry point not weak for clang Ammar Faizi
2022-03-20 19:16 ` Willy Tarreau
2022-03-21 11:38 ` Ammar Faizi
2022-03-21 17:27 ` Nick Desaulniers
2022-03-20 9:37 ` [RFC PATCH v1 3/6] tools/nolibc: i386: Implement syscall with 6 arguments Ammar Faizi
2022-03-20 10:33 ` Alviro Iskandar Setiawan
2022-03-20 10:42 ` Alviro Iskandar Setiawan
2022-03-20 15:09 ` Ammar Faizi
2022-03-20 13:10 ` David Laight
2022-03-20 14:01 ` Willy Tarreau
2022-03-20 15:04 ` Ammar Faizi
2022-03-20 18:22 ` David Laight [this message]
2022-03-20 9:37 ` [RFC PATCH v1 4/6] tools/nolibc/sys: Implement `mmap()` and `munmap()` Ammar Faizi
2022-03-20 9:37 ` [RFC PATCH v1 5/6] tools/nolibc/stdlib: Implement `malloc()`, `calloc()`, `realloc()` and `free()` Ammar Faizi
2022-03-20 15:50 ` Alviro Iskandar Setiawan
2022-03-20 16:10 ` Ammar Faizi
2022-03-20 16:16 ` Willy Tarreau
2022-03-20 16:36 ` Ammar Faizi
2022-03-20 16:46 ` Willy Tarreau
2022-03-20 9:37 ` [RFC PATCH v1 6/6] tools/include/string: Implement `strdup()` and `strndup()` Ammar Faizi
2022-03-20 15:55 ` Alviro Iskandar Setiawan
2022-03-20 16:10 ` Ammar Faizi
2022-03-21 7:53 ` Willy Tarreau
2022-03-21 8:16 ` Alviro Iskandar Setiawan
2022-03-21 8:51 ` Willy Tarreau
2022-03-21 11:36 ` Ammar Faizi
2022-03-21 11:43 ` Willy Tarreau
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