Messages in this thread | | | Date | Wed, 20 Oct 2004 10:19:41 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCH] include all vmas with unbacked pages in ELF core dumps |
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On Wed, 20 Oct 2004, Roland McGrath wrote: > > This patch changes the criteria for including vm regions in a core dump. > In recent glibc, the dynamic linker uses mprotect on part of a data segment > to write-protect pages that should never be touched after startup time > (this makes it harder for exploits to clobber indirection tables and the like). > Currently, this part of the segment is omitted from core dumps, losing > information about what the program did before it died.
Augh. Not all filesystems support holes, and I think VM_SHARED should trump VM_WRITE.
In general, I'd much prefer just adding a VM_DIRTY flag, and making the COW logic set it. That should guarantee that we write out the minimal required sections.
> Including unreadable regions gives you things like guard pages, showing > an accurate representation of of those in the core dump image. Since we > now have the ZERO_PAGE check, this won't actually write any more pages > to disk for those cases.
But any non-dumped section _will_ show up in the ELF headers, so things like guard pages have nothing to do with "maydump()", imho. And as mentioned, some filesystems _will_ write many more pages.
So if gdb has trouble with guard pages, pls get somebody to fix gdb instead, and tell them what the difference between p_filesz and p_memsz is. Putting them into the dump is just stupid.
So "maydump()" might sanely look something like
/* Shared or IO mappings are never written out */ if (vma->vm_flags & (VM_IO | VM_SHARED | VM_SHM)) return 0;
/* * Was the mapped backing store opened for writing? * This really only happens for VM_SHARED (which we * don't write out anyway), but it's conceptually * the right thing to do. Some future internal use * might end up doing this. */ if (!(vma->vm_flags & VM_MAYWRITE)) return 0;
/* We really should add this flag */ if (!(vma->vm_flags & VM_DIRTY)) return 0;
/* otherwise, write it out */ return 1;
and that should make people happy. No?
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