Messages in this thread | | | From | Andrew Lutomirski <> | Date | Wed, 20 Jul 2011 14:19:13 -0400 | Subject | Re: [PATCH 3/3] um: Implement a x86_64 vDSO |
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On Wed, Jul 20, 2011 at 2:09 PM, Richard Weinberger <richard@nod.at> wrote: > Am Mittwoch 20 Juli 2011, 19:54:02 schrieb Andy Lutomirski: >> On 07/18/2011 09:07 AM, Richard Weinberger wrote: >> > Until now UML had no x86_64 vDSO. >> > So glibc always used the vsyscall page for gettimeday() >> > and friends. >> > Calls to gettimeday() returned falsely the host time and >> > confused some programs. >> > >> > This patch adds a vDSO which turns all __vdso_* calls into >> > a system call so that UML can trap them. >> > >> > As glibc still uses the vsyscall page for static binaries this >> > patch improves the situation only for dynamic binaries. >> > >> > Signed-off-by: Richard Weinberger<richard@nod.at> >> > >> > + asm("syscall" : "=a" (ret) : >> > + "0" (__NR_clock_gettime), "D" (clock), "S" (ts) : "memory"); >> > + >> >> The x86-64 ABI and glibc think that rcx, and r11 are clobbered. glibc >> also thinks that cc is clobbered. I personally think that rdx and >> r8-r15 ought to be clobbered under the principle that syscall should >> look like a function call. > > Hmm, I thought my implementation is fine because it follows > arch/x86/vdso/vclock_gettime.c (Linus' tree). > > notrace static long vdso_fallback_gettime(long clock, struct timespec *ts) > { > long ret; > asm("syscall" : "=a" (ret) : > "0" (__NR_clock_gettime),"D" (clock), "S" (ts) : "memory"); > return ret; > } > > Am I missing something or needs vdso_fallback_gettime() also some updates?
vdso_fallback_gettime is going away :)
I haven't read all of the sysret code paths, but it looks like at least r11 is used in a comment. That being said, your code is an uninlinable function, and functions already clobber all those registers, so the code shouldn't cause problems in real life.
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