On Thu, May 15, 2014 at 12:53 PM, Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote: > 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? Look at its callers in vdso32-setup.c and/or vma.c, depending on version. > >> >> > >> > [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 Aha. Give tip/x86/vdso or -next a try or boot a 32-bit 3.15-rc kernel and you'll see it. --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>