linux-kernel - Re: Is gcc thread-unsafe?

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Message-ID: <20071026190856.18510fc4@the-village.bc.nu>
Date:	Fri, 26 Oct 2007 19:08:56 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	"Bart Van Assche" <bart.vanassche@...il.com>
Cc:	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Andrew Haley" <aph@...hat.com>
Subject: Re: Is gcc thread-unsafe?

> non-volatile variables. But for asm statements this can be solved by
> adding memory to the list of clobbered registers -- this will prevent
> any reordering of manipulations of non-volatile variables and asm
> statements.

IFF the processor doesn't reorder them in hardware, which on some
processors is visibly out of order when viewed from an I/O device or
another CPU.

You can stop the compiler but not the CPU - and some processors will
certainly speculatively load across conditionals, reorder writes etc

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