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libgo patch committed: don't use runtime_lock in __go_get_backtrace_state

From: Ian Lance Taylor <iant at golang dot org>
To: gcc-patches <gcc-patches at gcc dot gnu dot org>, "gofrontend-dev at googlegroups dot com" <gofrontend-dev at googlegroups dot com>
Date: Fri, 21 Jul 2017 11:27:45 -0700
Subject: libgo patch committed: don't use runtime_lock in __go_get_backtrace_state
Authentication-results: sourceware.org; auth=none

If getSiginfo in libgo does not know how to determine the PC, it will
call runtime_callers. That can happen in a thread that was started by
non-Go code, in which case the TLS variable g will not be set, in
which case runtime_lock will crash.

Avoid the problem by using atomic operations for the lock. This is OK
since creating a backtrace state is fast and never blocks.

The test case is TestCgoExternalThreadSIGPROF in the runtime package
on a system that getSiginfo doesn't handle specially.

Bootstrapped and ran Go testsuite on x86_64-pc-linux-gnu and
powerpc64le-unknown-linux-gnu.  Committed to mainline.

Ian

Attachment: patch.txt
Description: Text document

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