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SubjectRe: gnu asm help...
On 19 Jun 01 at 13:21, Richard B. Johnson wrote:
> On Tue, 19 Jun 2001, Timur Tabi wrote:
> > Oh, I see the problem. You could do something like this:
> >
> > cli
> > mov %0, %%eax
> > inc %%eax
> > mov %%eax, %0
> > sti
> >
> > and then return eax, but that won't work on SMP (whereas the "lock inc" does).
> > Doing a global cli might work, though.

Use spinlocks instead of global cli. Global cli can take milliseconds.

> The Intel book(s) state that an interrupt is not acknowledged until
> so many clocks (don't remember the number) after a stack operation.

Reread it. It says 'after operation with ss' - that is after
"mov xxxx,%ss" or "pop %ss", as it is expected that next instruction
will be "movl yyyy,%esp".

Before "lss ...." (it is lss in intel mnemonic...) was invented, you
could not switch your stack safely without this feature, as NMI could
arrive in the middle of your stack switch without blocking all interrupts
after "mov xxxx,%ss".

BTW, if you chain "mov %eax,%ss" back to back, they are executed
in pairs - irq can arrive after even mov, but cannot after odd (at
least on PII and PIII). But it is a bit off topic for L-K (except that
we can try other clones, maybe someone got it wrong?)
Best regards,
Petr Vandrovec
vandrove@vc.cvut.cz


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