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Re: gcc feature request / RFC: extra clobbered regs
- From: "H. Peter Anvin" <hpa at zytor dot com>
- To: Jakub Jelinek <jakub at redhat dot com>, Vladimir Makarov <vmakarov at redhat dot com>
- Cc: Andy Lutomirski <luto at kernel dot org>, gcc at gcc dot gnu dot org, "linux-kernel at vger dot kernel dot org" <linux-kernel at vger dot kernel dot org>, Linus Torvalds <torvalds at linux-foundation dot org>, Ingo Molnar <mingo at kernel dot org>, Thomas Gleixner <tglx at linutronix dot de>
- Date: Wed, 01 Jul 2015 23:16:40 -0700
- Subject: Re: gcc feature request / RFC: extra clobbered regs
- Authentication-results: sourceware.org; auth=none
- References: <CALCETrX6j9vBZR7RirXf8usz1Y4f-1TnVaYTVg0_PgQCeWZnRg at mail dot gmail dot com> <20150630213736 dot GQ10247 at tucnak dot redhat dot com> <559405E5 dot 7000405 at redhat dot com> <20150701153133 dot GY10247 at tucnak dot redhat dot com> <559424D4 dot 6010908 at redhat dot com> <20150701174333 dot GA10247 at tucnak dot redhat dot com>
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