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

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Date:	Wed, 1 Jul 2015 10:38:26 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Vladimir Makarov <vmakarov@...hat.com>
Cc:	Jakub Jelinek <jakub@...hat.com>,
	Andy Lutomirski <luto@...nel.org>, gcc@....gnu.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: gcc feature request / RFC: extra clobbered regs

On Wed, Jul 1, 2015 at 10:35 AM, Vladimir Makarov <vmakarov@...hat.com> 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.

I think it should be part of the type.  This shouldn't compile:

void func(void) __attribute__((used_reg("r12")));
void (*x)(void);
x = func;

--Andy
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