Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386)

Borislav Petkov
2011-08-23T16:23:12Z

On Tue, Aug 23, 2011 at 12:11:43PM -0400, Andrew Lutomirski wrote:
> In any case, this seems insanely overcomplicated. I'd be less afraid
> of something like my approach (which, I think, makes all of the
> SYSCALL weirdness pretty much transparent to ptrace users) or of just
> removing SYSCALL entirely from 32-bit code.

I don't think that removing SYSCALL from 32-bit code just so that UML
trapped syscalls work is something we'd like since SYSCALL is much
cheaper than INT $0x80:

"As a result, SYSCALL and SYSRET can take fewer than one-fourth the
number of internal clock cycles to complete than the legacy CALL and RET
instructions."

http://support.amd.com/us/Processor_TechDocs/24593.pdf, p. 152.

I know, it is 32-bit syscall on 64-bit kernel which should be pretty
rare but still...

Thanks.

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