Re: [patch] spinlocks: remove 'volatile'

[Linus Torvalds <torvalds@osdl.org>]

On Sun, 9 Jul 2006, Keith Owens wrote:
> 
> This disagrees with the gcc (4.1.0) docs.  info --index-search='Extended Asm' gcc
> 
>   The ordinary output operands must be write-only; GCC will assume
>   that the values in these operands before the instruction are dead and
>   need not be generated.  Extended asm supports input-output or
>   read-write operands.  Use the constraint character `+' to indicate
>   such an operand and list it with the output operands.  You should
>   only use read-write operands when the constraints for the operand (or
>   the operand in which only some of the bits are to be changed) allow a
>   register.

I'm fairly sure the docs are outdated (but may well be correct for older 
gcc versions - as I already discussed elsewhere, that "+" thing was not 
historically useful).

We've been using "+m" for some time in the kernel on several 
architectures.

git aficionados can do

	git grep -1 '"+m"' v2.6.17

to see the pre-existing usage of this (most of them go back a lot further, 
although some of them are newer - the <asm-i386/bitops.h> ones were added 
in January.

So if "+m" didn't work, we've been in trouble for at least the last year.

			Linus
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