Messages in this thread | | | Date | Tue, 23 Aug 2011 12:15:58 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386) |
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On 08/23/2011 09:22 AM, Borislav Petkov wrote: > 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... >
Right, but if you had said the difference had disappeared on current AMD silicon it would be much less of an issue. That's why I wanted to find that bit out from you.
-hpa
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