linux-kernel - Re: VDSO gettimeofday() x86

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAAZUjxD8-kA5325+OT0tANi0vUwcSRwT+VYaEd2LZ9cJrw0xUA@mail.gmail.com>
Date:	Tue, 16 Oct 2012 14:43:14 -0500
From:	wilson self <wself00@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: VDSO gettimeofday() x86_64 linux 3.2

I am just using gcc timetest.c -o timetest

Should be dynamically linked. glibc is 2.5, which is quite old, but I
think this should still work with it, no?

On Tue, Oct 16, 2012 at 2:39 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Tue, Oct 16, 2012 at 12:33 PM, wilson self <wself00@...il.com> wrote:
>> current_clocksource is tsc.
>>
>> the entire source of the test application:
>> ---
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <sys/time.h>
>> #include <time.h>
>>
>> int main() {
>>       struct timeval tim;
>>       gettimeofday(&tim, NULL);
>>       printf("%.6lf seconds\n", tim.tv_sec+tim.tv_usec/1000000.0);
>> }
>> ---
>> nothing fancy going on here.
>>
>> thanks for the help.
>
> There's lots of hidden fanciness.  What glibc version are you using
> and how are you linking to glibc?  All but the newest glibc versions
> use the old vsyscall when statically linked.  The newest versions use
> the syscall instead.  If you're dynamically linking, then gettimeofday
> should be okay even with fairly old glibc versions.
>
> (FWIW, glibc maintainership has changed since this was decided.  Feel
> free to bug the new maintainers if you care about statically-linked
> performance.  The only other runtime library I know of that uses the
> vdso or vsyscalls is Go, and the newest versions do the right thing.)
>
> --Andy
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/