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From: Willy Tarreau <w@1wt.eu>
To: Borislav Petkov <bp@alien8.de>
Cc: Ammar Faizi <ammar.faizi@students.amikom.ac.id>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH] tools/nolibc: x86: Remove `r8`, `r9` and `r10` from the clobber list
Date: Wed, 13 Oct 2021 14:51:42 +0200	[thread overview]
Message-ID: <20211013125142.GD5485@1wt.eu> (raw)
In-Reply-To: <YWbUbSUVLy/tx7Zu@zn.tnic>

Hi Boris,

On Wed, Oct 13, 2021 at 02:43:25PM +0200, Borislav Petkov wrote:
> On Wed, Oct 13, 2021 at 05:23:11AM +0700, Ammar Faizi wrote:
> > "Figure 3.4: Register Usage" is not the answer, if it were, nolibc.h
> > would be broken as it is missing "rdi", "rsi", "rdx" in the clobber list.
> 
> It is not about what happens in practice but what the contract is:
> syscall argument registers can potentially get clobbered and userspace
> should treat them as such. Because if the kernel decides to actually
> clobber them for whatever reason and some userspace thing thinks
> otherwise, then it is the userspace thing's problem as it doesn't adhere
> to the well known ABI.

I agree and that's why my question was about that authoritative doc, to
know the contract (since this one will not change under our feet). But
according to the doc you pointed, here the contract for syscalls is that
only rcx and r11 are clobbered (and rax gets the result). If so, I'm
personally fine with this.

Thanks,
Willy

  reply	other threads:[~2021-10-13 12:52 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-11  4:03 [PATCH] tools/nolibc: x86: Remove `r8`, `r9` and `r10` from the clobber list Ammar Faizi
2021-10-12  5:28 ` Willy Tarreau
2021-10-12  8:36   ` Ammar Faizi
2021-10-12  9:06     ` Willy Tarreau
2021-10-12 20:29       ` Borislav Petkov
2021-10-12 21:51         ` Borislav Petkov
2021-10-12 22:23         ` Ammar Faizi
2021-10-13  3:01           ` Willy Tarreau
2021-10-13  3:32             ` Ammar Faizi
2021-10-13  3:34               ` Ammar Faizi
2021-10-13  3:37                 ` Ammar Faizi
2021-10-13 12:43           ` Borislav Petkov
2021-10-13 12:51             ` Willy Tarreau [this message]
2021-10-13 13:06               ` Borislav Petkov
2021-10-13 14:07                 ` Willy Tarreau
2021-10-13 14:20                   ` Borislav Petkov
2021-10-13 14:24                     ` Willy Tarreau
2021-10-13 16:24                       ` Michael Matz
2021-10-13 16:30                         ` Willy Tarreau
2021-10-13 16:51                           ` Andy Lutomirski
2021-10-13 16:52                           ` Borislav Petkov
2021-10-14  8:44                             ` Ammar Faizi
2021-10-14 12:44                             ` Michael Matz
2021-10-14 14:31                               ` Borislav Petkov
2021-10-19  9:06                         ` David Laight
2021-10-23 20:40             ` H. Peter Anvin
2021-10-12 21:21       ` David Laight
2021-10-12 23:02         ` Subject: " Ammar Faizi
2021-10-13  9:03 ` [PATCH v2] " Ammar Faizi
2021-10-15  8:25   ` [PATCH 0/2] Fix clobber list and startup code bug Ammar Faizi
2021-10-15  8:25     ` [PATCH 1/2] tools/nolibc: x86: Remove `r8`, `r9` and `r10` from the clobber list Ammar Faizi
2021-10-18  5:52       ` Willy Tarreau
2021-10-15  8:25     ` [PATCH 2/2] tools/nolibc: x86-64: Fix startup code bug Ammar Faizi
2021-10-15  8:57       ` Ammar Faizi
2021-10-15  9:26         ` Bedirhan KURT
2021-10-15  9:58           ` Ammar Faizi
2021-10-15  9:41         ` Louvian Lyndal
2021-10-18  4:58       ` Willy Tarreau
2021-10-18  6:53         ` Ammar Faizi
2021-10-23 13:27           ` Ammar Faizi
2021-10-23 13:43             ` Willy Tarreau
2021-10-24  2:11               ` [PATCHSET v2 0/2] tools/nolibc: Fix startup code bug and small improvement Ammar Faizi
2021-10-24  2:11                 ` [PATCH 1/2] tools/nolibc: x86-64: Fix startup code bug Ammar Faizi
2021-10-24  2:11                 ` [PATCH 2/2] tools/nolibc: x86-64: Use `mov $60,%eax` instead of `mov $60,%rax` Ammar Faizi
2021-10-24 11:41                 ` [PATCHSET v2 0/2] tools/nolibc: Fix startup code bug and small improvement Willy Tarreau

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