On Tue, 15 Feb 2011, Carlos O'Donell wrote: > On Mon, Feb 14, 2011 at 8:58 PM, John David Anglin > <dave@xxxxxxxxxxxxxxxxxx> wrote: > > Feb 14 07:48:06 mx3210 kernel: INEQUIVALENT ALIASES: page 0x4282e520 addr 0x411e > > 8000 in file libc-2.11.2.so with flags 0x8000071 > > > > i haven't tracked down where these come from but this looks like a glibc issue. > > Note the final vm_flags value for the final map. This is the inequivalent one. > > As far as I know, the GCC testsuite does not play with MAP_FIXED maps. > > > > Carlos, any thoughts on where this might come from? > > Could you more clearly describe exactly what is the problem from > glibc's perspective? It's a little hard to tell since I haven't found the application the causes the above inequivalent aliases. >From a kernel perspective, we need to avoid multiple maps of the same memory page with inequivalent virtual addresses (i.e., the maps must start at the same address & 0x3fffff). Inequivalent maps only result from the use of MAP_FIXED. All the maps with VM_READ and VM_EXEC are equivalent in this case, so it's fairly clear that the map is for a code segment of libc-2.11.2.so. There is one map with just the VM_READ flag that is not equivalent. Because there are multiple maps to the same memory page, the page is in effect shared. Ideally, glibc should use equivalent aliases for all maps that it creates when they are "shared" as above. > The dynamic loader will do a non-fixed mapping to cover the entire > range of the PIC code needed to load into memory. This ensures it has > enough space to map segments. Then it follows up by using MAP_FIXED to > exactly map the segment from the file into memory. It also maps > remaining pages at MAP_FIXED from fd=-1 (zero fill). I tend to think this is the problem area. I will try to find a testcase. > Locale archives are also mapped in via MAP_FIXED (after a non-fixed mapping). > > Malloc uses MAP_FIXED and PROT_NONE (inaccessible) when shrinking > internal heaps e.g. it uses MAP_FIXED to single out the pages that are > no longer accessible (in a secure glibc it uses madvise > (MADV_DONTNEED). > > Malloc under some conditions may mremap with MREMAP_FIXED. > > Those are the glibc instances of MAP_FIXED maps that I can find. None of these appear to involve executable maps to a file. Dave -- J. David Anglin dave.anglin@xxxxxxxxxxxxxx National Research Council of Canada (613) 990-0752 (FAX: 952-6602) -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
