linux-kernel - Re: gcc feature request / RFC: extra clobbered regs

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Message-ID: <5594D748.2020304@zytor.com>
Date:	Wed, 01 Jul 2015 23:16:40 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jakub Jelinek <jakub@...hat.com>,
	Vladimir Makarov <vmakarov@...hat.com>
CC:	Andy Lutomirski <luto@...nel.org>, gcc@....gnu.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: gcc feature request / RFC: extra clobbered regs

On 07/01/2015 10:43 AM, Jakub Jelinek wrote:
> On Wed, Jul 01, 2015 at 01:35:16PM -0400, Vladimir Makarov wrote:
>> Actually it raise a question for me.  If we describe that a function
>> clobbers more than calling convention and then use it as a value (assigning
>> a variable or passing as an argument) and loosing a track of it and than
>> call it.  How can RA know what the call clobbers actually.  So for the
>> function with the attributes we should prohibit use it as a value or make
>> the attributes as a part of the function type, or at least say it is unsafe.
>> So now I see this as a *bigger problem* with this extension.  Although I
>> guess it already exists as we have description of different ABI as an
>> extension.
> 
> Unfortunately target attribute is function decl attribute rather than
> function type.  And having more attributes affect switchable targets will be
> non-fun.
> 

How on Earth does that work with existing switchable ABIs?  Keep in mind
that we already support multiple ABIs...

	-hpa


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