linux-kernel - Re: [PATCH 1/3] x86/entry: Clear extra registers beyond syscall arguments for 64bit kernels

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Message-ID: <20180205182957.xbeufjgyhd7pgdvq@gmail.com>
Date:   Mon, 5 Feb 2018 19:29:57 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Brian Gerst <brgerst@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <ak@...ux.intel.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 1/3] x86/entry: Clear extra registers beyond syscall
 arguments for 64bit kernels


* Andy Lutomirski <luto@...nel.org> wrote:

> [...] Clearing R10 is mostly useless in the syscall path because we'll just 
> unconditionally reload it in do_syscall_64().

AFAICS do_syscall_64() doesn't touch R10 at all. So how does it reload R10?

In fact do_syscall_64() as a C function does not touch R10, R11, R12, R13, R14, 
R15 - it passes their values through.

What am I missing?

Thanks,

	Ingo