On Thu, May 15, 2014 at 3:15 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > On Thu, May 15, 2014 at 2:57 PM, Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote: >> On Thu, May 15, 2014 at 02:42:48PM -0700, Andy Lutomirski wrote: >>> > >>> > Looking forward the question appear -- will VDSO_PREV_PAGES and rest of variables >>> > be kind of immutable constants? If yes, we could calculate where the additional >>> > vma lives without requiring any kind of [vdso] mark in proc/pid/maps output. >>> >>> Please don't! >>> >>> These might, in principle, even vary between tasks on the same system. >>> Certainly the relative positions of the vmas will be different >>> between 3.15 and 3.16, since we need almost my entire cleanup series >>> to reliably put them into their 3.16 location. And I intend to change >>> the number of pages in 3.16 or 3.17. >> >> There are other ways how to find where additional pages are laying but it >> would be great if there a straightforward interface for that (ie some mark >> in /proc/pid/maps output). > > I'll try to write a patch in time for 3.15. > My current draft is here: https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/log/?h=vdso/cleanups On 64-bit userspace, it results in: 7fffa1dfd000-7fffa1dfe000 r-xp 00000000 00:00 0 [vdso] 7fffa1dfe000-7fffa1e00000 r--p 00000000 00:00 0 [vvar] ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall] On 32-bit userspace, it results in: f7748000-f7749000 r-xp 00000000 00:00 0 [vdso] f7749000-f774b000 r--p 00000000 00:00 0 [vvar] ffd94000-ffdb5000 rw-p 00000000 00:00 0 [stack] Is this good for CRIU? Another approach would be to name both of these things "vdso", since they are sort of both the vdso, but that might be a bit confusing -- [vvar] is not static text the way that [vdso] is. If I backport this for 3.15 (which might be nasty -- I would argue that the code change is actually a cleanup, but it's fairly intrusive), then [vvar] will be *before* [vdso], not after it. I'd be very hesitant to name both of them "[vdso]" in that case, since there is probably code that assumes that the beginning of "[vdso]" is a DSO. Note that it is *not* safe to blindly read from "[vvar]". On some configurations you *will* get SIGBUS if you try to read from some of the vvar pages. (That's what started this whole thread.) Some pages in "[vvar]" may have strange caching modes, so SIGBUS might not be the only surprising thing about poking at 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>