linux-kernel - Re: ABI change for device drivers using future AVX instruction set

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Message-ID: <20080625211443.690855b9@lxorguk.ukuu.org.uk>
Date:	Wed, 25 Jun 2008 21:14:43 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Agner Fog <agner@...er.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: ABI change for device drivers using future AVX instruction set

> 3. When compiling a device driver, the compiler may insert implicit 
> calls to library functions such as memcpy and memset. These functions 
> typically have a CPU dispatcher that chooses the largest register size 
> available. The device driver may therefore use YMM registers without the 
> knowledge of the programmer and without compiling with the AVX switch on.

Linux uses its own routines in these cases - and in fact for MMX we
generally avoid kernel usage in order to avoid the overheads (ditto FP).

> A decision on this question should be made and published in the ABI so 
> that people can make compatible device drivers.

The beauty of the Linux kernel being source based - we don't have to worry
about ABI problems like this.

Alan

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