control: retitle -1 vsyscall is not in effect in static linked executable on jessie thanks
On 2016-04-24 21:01, jian wang wrote: > On Sun, Apr 24, 2016 at 6:31 PM, Aurelien Jarno <[email protected]> wrote: > > control: tag -1 + moreinfo > > > > On 2016-04-22 11:11, Mattia Rizzolo wrote: > >> control: reassign -1 libc6 2.19-18+deb8u4 > >> > >> On Fri, Apr 22, 2016 at 06:27:34PM +0800, jian wang wrote: > >> > Package: lib6 > >> > >> lost a 'c' :) > >> reassigning. > >> > >> > Version: 2.19-18+deb8u4 > >> > Severity: important > >> > > >> > vDSO is not in effect in static linked executable on jessie. This is > >> > not the case with wheezy. > >> > > >> > We build binary to run on both wheezy and jessie, so -static. When > >> > building platform is wheezy, vdso works fine, but jessie the opposite. > >> > > >> > This leads to performance hit. Unfortunately, we use g++ 4.9 for some > >> > application, so wheezy can't be used as build platform. > > > > There is not of information about your environment, so given what you > > describe, it seems you are using an i386 installation. > > > > The context is for lots of servers. We use amd64 all over datacenters. > > > The vDSO support requires at least a i686 CPU, while Debian i386 targets > > i586. When using dynamic linking, one can install libc6-i686 which > > provides an i686 optimized version of the libc, therefore with vDSO > > support. It is automatically loaded if the CPU supports it. > > > > In your case, given you use static linking, the i586 version of the libc > > is used, and it therefore doesn't support vDSO . That is true on wheezy, > > jessie, stretch, sid. I don't believe this is a regression, and in > > addition I can't reproduce it. > > > > No. > > We have looked into the code now. > > Glibc 2.13 (wheezy) uses an asm version of gettimeofday.S for x86_64 > which uses vDSO. To be more precise, glibc 2.13 uses vDSO for shared builds and vsyscall for static ones. > On the way up to glibc 2.19 (jessie), vDSO was rewritten into > gettimeofday.c. And as we dig out, Ulrich Drepper decided to not > optimize static linking, or even to dwarf static linking > > https://sourceware.org/bugzilla/show_bug.cgi?id=12813 vsyscalls are consider deprecated due to limitation and security consideration. I guess that the reason the vsyscall part of the code has been removed. Aurelien -- Aurelien Jarno GPG: 4096R/1DDD8C9B [email protected] http://www.aurel32.net
