linux-kernel - Re: [PATCH 3/9] x86/entry/32: fix the end of the stack for newly forked tasks

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Date:   Tue, 20 Sep 2016 22:33:04 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Brian Gerst <brgerst@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH 3/9] x86/entry/32: fix the end of the stack for newly
 forked tasks

On Tue, Sep 20, 2016 at 10:25:16PM -0500, Josh Poimboeuf wrote:
> On Tue, Sep 20, 2016 at 09:10:55PM -0400, Brian Gerst wrote:
> > Dropping asmlinkage from schedule_tail() would be a better option if possible.
> 
> My understanding is that it's still needed for ia64.  AFAICT, ia64
> relies on schedule_tail() having the syscall_linkage function attribute.
> From the gcc manual:
> 
>   This attribute is used to modify the IA64 calling convention by
>   marking all input registers as live at all function exits. This makes
>   it possible to restart a system call after an interrupt without having
>   to save/restore the input registers. This also prevents kernel data
>   from leaking into application code. 
> 
> And the ia64 entry code has some similar language:
> 
> 		/*
> 		 * Invoke schedule_tail(task) while preserving in0-in7, which may be needed
> 		 * in case a system call gets restarted.
> 		 */
> 	GLOBAL_ENTRY(ia64_invoke_schedule_tail)
> 		...

(But I should note that I'm a complete ia64 neophyte, so I could be
misreading that...)

-- 
Josh