linux-kernel - Re: [PATCH v3 1/4] x86/syscall: sign-extend system calls on entry to int

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Message-ID: <YKDOQxRS+kX1WhQq@gmail.com>
Date:   Sun, 16 May 2021 09:48:19 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/4] x86/syscall: sign-extend system calls on entry to
 int


* H. Peter Anvin <hpa@...or.com> wrote:

> This is an ABI change, but is in fact a revert to the original x86-64
> ABI. The original assembly entry code would zero-extend the system
> call number; this patch uses sign extend to be explicit that this is
> treated as a signed number (although in practice it makes no
> difference, of course) and to avoid people getting the idea of
> "optimizing" it, as has happened on at least two(!) separate
> occasions.

The original x86-64 ABI as documented by AMD, as we (probably) never had 
this in Linux, right?

Sounds sensible to do this, assuming nothing relies on the weirdness.

Thanks,

	Ingo