On Thu, May 15, 2014 at 1:45 AM, Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote: > On Wed, May 14, 2014 at 03:23:27PM -0700, Andy Lutomirski wrote: >> I can summarize: >> >> On 3.14 and before, the vdso is just a bunch of ELF headers and >> executable data. When executed by 64-bit binaries, it reads from the >> fixmap to do its thing. That is, it reads from kernel addresses that >> don't have vmas. When executed by 32-bit binaries, it doesn't read >> anything, since there was no 32-bit timing code. >> >> On 3.15, the x86_64 vdso is unchanged. The 32-bit vdso is preceded by >> a separate vma containing two pages worth of time-varying read-only >> data. The vdso reads those pages using PIC references. > > Andy, could you please point me where is the code which creates a second vma? > latest 3.15 master branch Search for _install_special_mapping in arch/x86/vdso. It's in a different place in 3.15-rc and -next. > > [root@fc ~]# cat /proc/self/maps > ... > 7fff57b6e000-7fff57b8f000 rw-p 00000000 00:00 0 [stack] > 7fff57bff000-7fff57c00000 r-xp 00000000 00:00 0 [vdso] > ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall] > [root@fc ~]# > What version and bitness is this? > Or you mean vsyscall area? If yes, then in criu we don't dump vsyscall zone. > On restore we don't touch vsyscall either but for vdso there are two cases vsyscalls are almost gone now :) > > - if there were no kernel change on vdso contents we simply use vdso provided > by the kernel at the moment of criu startup > > - if vdso has been changed and looks different from one saved in image during > checkpoint, we map it from image but then patch (push jmp instruction) so > when application calls for some of vdso function it jumps into vdso code > saved in image and then jumps into vdso mapped by the kernel (ie kind of > proxy calls) This force us to do own Elf parsing inside criu to calculate > proper offsets. Yuck :) --Andy -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>