On Thu, May 15, 2014 at 12:46:34PM -0700, Andy Lutomirski wrote: > 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. As far as I see _install_special_mapping allocates one vma from cache and vma->vm_start = addr; vma->vm_end = addr + len; so where is the second one? > > > > > [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? x86-64, 3.15-rc5 > > > 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 :) Good to know ;) > > > > > - 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 :) Yeah, I know, we simply had no choise. -- 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>