[Bug sanitizer/59258] ubsan: ICE(segfault): stack-buffer-overflow with -fsanitize=undefined

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59258

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 31289
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31289&action=edit
gcc49-pr59258.patch

Untested fix for the dwarf2out.c ICE.  The problem is that -fsanitize=null
will preserve in location_t of ADDR_EXPR a reference to a block, but the BLOCK
isn't referenced from anywhere else and thus during ggc_collect removed as
unused, then dwarf2out.c allocates the same GC memory for something else and
finally when processing the ADDR_EXPR the old BLOCK is modified again.

Either of the hunks in the patch should fix this, IMHO we want both, it doesn't
make sense to provide any locus for the ADDR_EXPR of the string in the static
ctor, and as ubsan_create_data compares loc to UNKNOWN_LOCATION in a bunch of
places, not doing LOCATION_LOCUS there means it might not compare to
UNKNOWN_LOCATION even when it actually is UNKNOWN_LOCATION just with some
non-NULL associated block.  Perhaps my
        * ubsan.c (ubsan_source_location): Don't crash on unknown locations.
change will be unneeded now?