[SeaBIOS] [PATCH] smp: Replace QEMU SMP init assembler code with C; run only in 32bit mode.

Kevin O'Connor kevin at koconnor.net
Sat May 31 17:00:45 CEST 2014

On Sat, May 31, 2014 at 12:12:13PM +0200, Paolo Bonzini wrote:
> Il 31/05/2014 03:20, Kevin O'Connor ha scritto:
> >Change the multi-processor init code to trampoline into 32bit mode on
> >each of the additional processors.  Implement an atomic lock so that
> >each processor performs its initialization serially.
> I don't see much benefit in this change, in fact the new code is more
> complex than the old one...

Thanks for reviewing!

The reason I implemented this is to reduce the amount of 16bit code.
The fw/smp.c file is currently being compiled in 16bit mode just to
pick up the ~30 lines of assembler.  I'd prefer to jump into 32bit
mode to avoid that.

As to converting the handler to C code - I agree with you on code
complexity, however I do think the existing assembler was already
sufficiently complex.  Also, being able to use dprintf() is quite

>But anyway, if you prefer to go this way I have
> just a couple observations on the patch:
> 1) acquiring the lock can be done simply by a "1: lock btsl; jc 1b"; no need
> to use the cmpxchg.

Thanks - that is an improvement.

> 2) There's no need to acquire the lock repeatedly in the BSP, I think
> writing the loop in assembly is acceptable:

I'll rework the patch and take a look at that.


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