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From: "H. Peter Anvin" <hpa@zytor.com>
To: Borislav Petkov <bp@alien8.de>,
	Ammar Faizi <ammar.faizi@students.amikom.ac.id>
Cc: Willy Tarreau <w@1wt.eu>,
	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
Subject: Re: [PATCH] tools/nolibc: x86: Remove `r8`, `r9` and `r10` from the clobber list
Date: Sat, 23 Oct 2021 13:40:59 -0700	[thread overview]
Message-ID: <8147f571-0da2-f20c-31dd-72ad56eb1ba0@zytor.com> (raw)
In-Reply-To: <YWbUbSUVLy/tx7Zu@zn.tnic>



On 10/13/21 05:43, 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.
> 

Currently the kernel doesn't, but some past kernels have zeroed some of 
these registers rather than preserving them.

	-hpa

  parent reply	other threads:[~2021-10-23 20:42 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
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 [this message]
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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