[Bug target/94087] std::random_device often fails when used from multiple threads
cvs-commit at gcc dot gnu.org
Thu Jul 9 09:14:09 GMT 2020
--- Comment #26 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jonathan Wakely
Author: Jonathan Wakely <email@example.com>
Date: Tue May 19 16:49:21 2020 +0100
libstdc++: Use RDRAND as fallback if RDSEED keeps failing (PR 94087)
It's not difficult for multiple threads to drain the entropy available
to the RDSEED instruction, at which point we throw an exception. This
change will try to use RDRAND after RDSEED fails repeatedly, and only
throw if RDRAND also fails repeatedly. This doesn't guarantee a random
value can always be read, but reduces the likelihood of failure when
using the RDSEED instruction.
* src/c++11/random.cc (__x86_rdseed): Allow fallback function to be
(__x86_rdseed_rdrand): New function that uses rdseed with rdrand
(random_device::_M_init): Use __x86_rdseed_rdrand when both
instructions are available.
* testsuite/26_numerics/random/random_device/94087.cc: New test.
(cherry picked from commit a2d196e75cef95c2b70734ad02e94f9da0e769fe)
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