Re: [Qemu-devel] FreeBSD clock_gettime()

[Peter Maydell]

On 2 June 2015 at 15:49, Stefan Hajnoczi <address@hidden> wrote:
> On Sun, May 31, 2015 at 07:11:25PM +0530, Sai Prajeeth wrote:
>> I have done experiments and it seems that FreeBSD's libc function
>> clock_gettime() results in a system call when running on QEMU whereas on
>> hardware it does not. Does anybody know why? For those interested , you can
>> find the clock_gettime libc call in freebsd source here:
>> https://github.com/lattera/freebsd/blob/master/lib/libc/sys/clock_gettime.c
>
> This is more of a FreeBSD kernel question than a QEMU question.  I don't
> have time to dig into the FreeBSD sources but you should be able to find
> the answer there.

The underlying answer is presumably "some difference between
the (emulated?) (KVM?) CPU QEMU exposes to the guest and the
CPU on real h/w makes FreeBSD decide it can't provide gettime
in the vdso". Exactly what that difference is you'd need to
look at the FreeBSD sources to find out, I agree.

-- PMM