libbacktrace patch committed: Fix threaded race

[Ian Lance Taylor]

Using libbacktrace more extensively from Go has revealed a race
condition in libbacktrace.  I cleverly save some memory by reusing a
vector in the DWARF data structure.  However, that is fairly hard to do
if multiple threads are simultaneously getting a backtrace.  This patch
changes the code to always use a new vector when threaded.  This will
introduce additional memory fragmentation, but that seems impossible to
avoid.  Bootstrapped and ran libbacktrace and Go testsuite on
x86_64-unknown-linux-gnu.  Committed to mainline.

Ian


2013-01-31  Ian Lance Taylor  <iant@google.com>

	* dwarf.c (read_function_info): Permit fvec parameter to be NULL.
	(dwarf_lookup_pc): Don't use ddata->fvec if threaded.


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