linux-kernel - Re: [PATCH 74/74] lto, workaround: Mark do_futex noinline to prevent clobbering ebp

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Message-ID: <50359FF8.7090609@zytor.com>
Date:	Wed, 22 Aug 2012 20:14:00 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <ak@...ux.intel.com>
CC:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	x86@...nel.org, mmarek@...e.cz, linux-kbuild@...r.kernel.org,
	JBeulich@...e.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 74/74] lto, workaround: Mark do_futex noinline to prevent
 clobbering ebp

On 08/22/2012 07:29 PM, Andi Kleen wrote:
> How about just use register arguments for the first three arguments.
> This should work for the syscalls at least (may be too risky for all
> other asm entry points)

Well, it's just an effort to convert each one in turn...

> And for syscalls with more than three generate a stub that saves on the stack
> explicitely.  This could be done using the new fancy SYSCALL definition macros
> (except that arch/x86 would need to start using them too in its own code)

I don't think there is any point.  Just push the six potential arguments 
to the stack and be done with it.

> Or is there some subtle reason with syscall restart and updated args
> that prevents it?
>
> Perhaps newer gcc can do regparm(X), X > 3 too, may be worth trying.

No, there is no such ABI defined.

> Don't have time to look into this currently though.

Always the problem.

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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