I am curious about this article:
http://www.linuxjournal.com/content/creating-vdso-colonels-other-chicken
and openSUSE's supplied kernel. I see that VDSO's are enabled in
openSUSE distros:
$ cat /proc/self/maps | grep vdso
ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
If I look in /usr/src/linux/arch/x86/vdso/vdso.lds.S, I see:
/*
* This controls what userland symbols we export from the vDSO.
*/
VERSION {
LINUX_2.6 {
global:
clock_gettime;
__vdso_clock_gettime;
gettimeofday;
__vdso_gettimeofday;
getcpu;
__vdso_getcpu;
local: *;
};
}
As it turns out, gettimeofday is a function our app uses extensively. It
is a data collection program that time tags everything.
Is it the case that applications should just magically get the VDSO
version of the three system calls listed above? If that is the case, I
should not see calls to gettimeofday in straces of my app. But I do.
I suspect there is is an additional step needed. I have not recognized
it in my googling on the topic. Perhaps a compile/linker option?
Yours sincerely,
Roger Oberholtzer
OPQ Systems / Ramböll RST
Office: Int +46 10-615 60 20
Mobile: Int +46 70-815 1696
roger.oberholtzer(a)ramboll.se
________________________________________
Ramböll Sverige AB
Krukmakargatan 21
P.O. Box 17009
SE-104 62 Stockholm, Sweden
www.rambollrst.se
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