[Libunwind-devel] Crash in libunwind 0.99 on x86_64

[Dave Wright]

I got a crash in libunwind (called from tcmalloc) on Ubuntu 0910 x86_64 (stack trace is below). It looks like it's trying to read address 0x8, which obviously is not valid. I noticed a post from a month ago where an explicit check was added for access to page 0, and a followup that mentioned msync doesn't reliably catch certain invalid accesses:

http://lists.gnu.org/archive/html/libunwind-devel/2009-12/msg00002.html

..I'm assuming the explicit check will prevent my specific crash in this instance, but my real question is whether libunwind is "reliable" enough on x86_64 to use in a production application during runtime (as tcmalloc does for sampling purposes) - as opposed to using it just for profiling / crash stack dumping. Some of the posts on this list would seem to indicate that the library does have a non-zero chance of segfaulting in some situations, which would seem to indicate that it isn't appropriate for use as a runtime feature of a production app.

In case it helps, here is the stack trace of the libunwind crash I got (I have the full core file if someone wants to debug it further).

http://pastebin.org/162078

-Dave Wright