Messages in this thread | | | Date | Wed, 20 Jul 2011 13:54:02 -0400 | From | Andy Lutomirski <> | Subject | Re: [PATCH 3/3] um: Implement a x86_64 vDSO |
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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.
It's hard to imagine this causing a problem in a function this trivial, though.
This applies to the other two syscall instructions as well.
--Andy
P.S. If you really care, with the changes in tip/x86/vdso, it ought to be possible for UML to trap vsyscalls as well. This would need a change to do_emulate_vsyscall to honor TIF_SYSCALL_EMU with intelligent semantics. I know nothing about ptrace, so I'm not volunteering :)
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