[Bug other/46954] New: FDEs possibly left unsorted in unwind-dw2-fde.c

["jvoung at google dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46954

           Summary: FDEs possibly left unsorted in unwind-dw2-fde.c
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jvoung@google.com


Not completely sure if this is a bug in GCC or my toolchain, but I have been
able to trigger a situation where _Unwind_Find_FDE is unable to find an FDE. In
my case, the reason is that the FDEs are only partially sorted even though
"ob->s.b.sorted = 1", so the binary search (binary_search_mixed_encoded_fdes in
particular) fails.

By patching end_fde_sort() with:

--- a/llvm-gcc-4.2/gcc/unwind-dw2-fde.c
+++ b/llvm-gcc-4.2/gcc/unwind-dw2-fde.c
@@ -588,6 +588,11 @@
       fde_split (ob, fde_compare, accu->linear, accu->erratic);
       gcc_assert (accu->linear->count + accu->erratic->count == count);
       frame_heapsort (ob, fde_compare, accu->erratic);
+      frame_heapsort (ob, fde_compare, accu->linear);
       fde_merge (ob, fde_compare, accu->linear, accu->erratic);
       free (accu->erratic);
     }

The FDEs are fully sorted and binary search succeeds.

I don't know the code well at all, but is the patch correct, or should
accu->linear already be sorted? In the else-branch, the code does a heap sort
on accu->linear, which leads me to believe that it accu->linear may be unsorted
(and so should be sorted as well).