Messages in this thread | | | Date | Sat, 8 Jul 2006 23:50:10 +0100 | From | Ralf Baechle <> | Subject | Re: [patch] spinlocks: remove 'volatile' |
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On Thu, Jul 06, 2006 at 01:34:14PM -0700, Linus Torvalds wrote:
> On Thu, 6 Jul 2006, Linus Torvalds wrote: > > > > So I _think_ that we should change the "=m" to the much more correct "+m" > > at the same time (or before - it's really a bug-fix regardless) as > > removing the "volatile". > > Here's a first cut (UNTESTED!) for x86. I didn't check any other > architectures, I bet they have similar problems.
I tried the same on MIPS, for lazyness sake at first only in atomic.h. With gcc 3.3 the code size is exactly the same with both "=m" and "+m", so I didn't look into details of the generated code. With gcc 4.1 "+m" results in a size increase of about 1K for the ip27_defconfig kernel. For example:
<unlock_kernel>: df830000 ld v1,0(gp) 8c620028 lw v0,40(v1) 04400014 bltz v0,a80000000029944c <unlock_kernel+0x5c> 00000000 nop 2442ffff subiu v0,v0,1 ac620028 sw v0,40(v1) # current->lock_depth 8c630028 lw v1,40(v1) # current->lock_depth 0461000b bgez v1,a80000000029943c <unlock_kernel+0x4c>
The poinless load isn't generated with "=m". The interesting thing is that in all the instances of bloat I looked at it was actually happening not as part of the asm statement itself, so maybe gcc's reload is getting a little confused.
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