[uml-devel] Re: Fixing fp-state handling

[uml-devel] Re: Fixing fp-state handling

[Bodo Stroesser]

Blaisorblade wrote:
> From arch/um/os-Linux/sys-i386/registers.c:
> 
> /* XXX These need to use [GS]ETFPXREGS and copy_sc_{to,from}_user_skas needs
>  * to pass in a sufficiently large buffer
>  */
> 
> Could fixing this be the real fix instead of "fp-state" in the incrementals?
Sorry, no, it could't.

fp-state fixes a wrong handling of fp-/fpx-regs in arch/um/sys-i386/signal.c,
which causes fp-regs of user's "main" routine to be modified, if a signal-handler
interrupting "main" uses fp.

IMHO, the patch is OK in that it fixes the problem (Please note, Jeff had a
currupted version of the patch in his incrementals for some weeks, that didn't
work and even resulted in worse behavior. The current one is OK.).

What I don't like in the patch, is the duplicated code for fp to fpx conversion
(and vice versa). That code is stolen and modified from arch/um/sys-i386/ptrace.c
resp. arch/i386/kernel/i387.c. I think, arch/um/sys-i386/ptrace.c should be
reworked to do fp/fpx conversions in memory as signal.c now does. Doing the rework
ptrace.c also should be extended to support coredumping fp/fpx-regs. All this
were the reasons to call fp-state a "quick and dirty" patch.
Unfortunately I can't do this myself for the moment, because I have to bring up
UML-s390 as fast as possible. So maybe the best thing currently is to use fp-state.

BTW: having fp-state applied, save_fp_registers and restore_fp_registers in
arch/um/os-Linux/sys-i386/registers.c are no longer needed and might be removed.

		Bodo


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