Re: Linux Jobs as of 2.3.99pre6-5

From: Jamie Lokier (
Date: Tue Apr 25 2000 - 10:16:40 EST

Richard B. Johnson wrote:
> > fix kernel handling of %fs and %gs registers on x86
> >
> > ?? It's preventing major optimizations in the thread library.
> >
> Previously, no kernel code I've seen used these registers so they are
> never touched during a context-switch. If these are now used by the C
> compiler, it is the responsibility of that compiler to preserve the
> segment registers in its code generation so a potential problem has
> been overlooked.

The C compiler doesn't touch %fs or %gs, so in principle they don't need
to be saved due to kernel entry/exit. But something is clobbering them.
Probably the restore code, which has a path which zeros a descriptor if
reloading it fails for some reason.

-- Jamie

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