Messages in this thread | | | Date | Wed, 30 Sep 2009 13:19:54 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: Linux 2.6.32-rc1 |
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On Wed, 30 Sep 2009, Arjan van de Ven wrote: > +ENTRY(cmpxchg8b_emu) > + CFI_STARTPROC > + > + push %edi > + push %ebx > + push %ecx > + /* disable interrupts */ > + pushf > + pop %edi > + cli > + > + cmpl %edx, 4(%esi) > + jne 1f > + cmpl %eax, (%esi) > + jne 1f > + > + xchg (%esi), %ebx > + xchg 4(%esi), %ecx > + mov %ebx, %eax > + mov %ecx, %edx
Ok, so why do you do this? You've just checked that the 8 bytes at esi are the same as edx:eax, why do you do that odd xchg?
Why isn't this part just
mov %ebx,(%esi) mov %ecx,4(%esi)
and leave ebx/ecx alone?
I also don't see why you play games with eflags and %edi. Just leave the flags on the stack. So it all would look like
# # Emulate 'cmpxchg8b (%esi)' except we don't # set the whole ZF thing (caller will just # compare eax:edx with the expected value) # cmpxchg8b_emu: pushfl cli cmpl (%esi),%eax jne not_same cmpl 4(%esi),%edx jne not_same movl %ebx,(%esi) movl %ecx,4(%esi) popfl ret not_same: movl (%esi),%eax movl 4(%esi),%edx popfl ret
I dunno. You _could_ use edi/ebp as a temporary for 'dest' to only do the load once (and add push/pop to save the registers), but it's not like the above is really atomic anyway, and it very much depends on 'cli' just making sure that nothing else happens. So the above seems to be the simplest emulation, considering the interfaces..
UNTESTED! I wrote this in an email editor. I haven't assembled it or verified the semantics or workingness in any way, shape or form.
Linus
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