On Wed, 2006-07-26 at 10:27 -0700, Jeremy Fitzhardinge wrote:
> In your sequences in asm/paravirt.h, you explicitly save the caller-save
> regs:
>
> static inline void raw_local_irq_restore(unsigned long f)
> {
> __asm__ __volatile__(paravirt_alt("pushl %%ecx; pushl %%edx\n\t"
> "pushl %1; call *%0\n\t"
> "popl %1; popl %%edx; popl %%ecx",
> PARAVIRT_RESTORE_FLAGS)
> : : "m" (paravirt_ops.restore_fl), "a"(f)
> : "memory");
> }
>
> Wouldn't adding ecx/edx (and maybe eax, where it has no other use) to
> the asm's clobber list be sufficient?
Absolutely. I didn't know how much room the replacements would need, so
I chose this "no-clobber" approach which takes 12 bytes. If it turns
out that is too much, we can change to a clobber. If it turns out to be
too little, we'll need to noop pad and/or clobber.
For the cases where these are used in asm directly (currently cli and
sti replacement), it was simplest to save all regs to have to same
non-clobber properties as the raw insns.
Hope that clarifies my thinking,
Rusty.
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