public inbox for libstdc++-cvs@sourceware.org help / color / mirror / Atom feed
From: Tamar Christina <tnfchris@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc(refs/vendors/ARM/heads/arm-perf-staging)] libstdc++: Use RDRAND as fallback if RDSEED keeps failing (PR 94087) Date: Fri, 17 Jul 2020 15:38:51 +0000 (GMT) [thread overview] Message-ID: <20200717153851.2D7693945C2D@sourceware.org> (raw) https://gcc.gnu.org/g:bbf9d358ae2104a09fc1b61e2b818928b6591831 commit bbf9d358ae2104a09fc1b61e2b818928b6591831 Author: Jonathan Wakely <jwakely@redhat.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. PR libstdc++/94087 * src/c++11/random.cc (__x86_rdseed): Allow fallback function to be passed in. (__x86_rdseed_rdrand): New function that uses rdseed with rdrand fallback. (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) Diff: --- libstdc++-v3/src/c++11/random.cc | 26 ++++++++- .../26_numerics/random/random_device/94087.cc | 63 ++++++++++++++++++++++ 2 files changed, 87 insertions(+), 2 deletions(-) diff --git a/libstdc++-v3/src/c++11/random.cc b/libstdc++-v3/src/c++11/random.cc index 236eccfc177..62ed274479a 100644 --- a/libstdc++-v3/src/c++11/random.cc +++ b/libstdc++-v3/src/c++11/random.cc @@ -97,7 +97,7 @@ namespace std _GLIBCXX_VISIBILITY(default) #if USE_RDSEED unsigned int __attribute__ ((target("rdseed"))) - __x86_rdseed(void*) + __x86_rdseed(void* fallback) { unsigned int retries = 100; unsigned int val; @@ -105,12 +105,25 @@ namespace std _GLIBCXX_VISIBILITY(default) while (__builtin_ia32_rdseed_si_step(&val) == 0) { if (--retries == 0) - std::__throw_runtime_error(__N("random_device: rdseed failed")); + { + if (auto f = reinterpret_cast<unsigned int(*)(void*)>(fallback)) + return f(nullptr); + std::__throw_runtime_error(__N("random_device: rdseed failed")); + } __builtin_ia32_pause(); } return val; } + +#if USE_RDRAND + unsigned int + __attribute__ ((target("rdseed,rdrnd"))) + __x86_rdseed_rdrand(void*) + { + return __x86_rdseed(reinterpret_cast<void*>(&__x86_rdrand)); + } +#endif #endif #ifdef _GLIBCXX_USE_CRT_RAND_S @@ -205,6 +218,15 @@ namespace std _GLIBCXX_VISIBILITY(default) __cpuid_count(7, 0, eax, ebx, ecx, edx); if (ebx & bit_RDSEED) { +#ifdef USE_RDRAND + // CPUID.01H:ECX.RDRAND[bit 30] + __cpuid(1, eax, ebx, ecx, edx); + if (ecx & bit_RDRND) + { + _M_func = &__x86_rdseed_rdrand; + return; + } +#endif _M_func = &__x86_rdseed; return; } diff --git a/libstdc++-v3/testsuite/26_numerics/random/random_device/94087.cc b/libstdc++-v3/testsuite/26_numerics/random/random_device/94087.cc new file mode 100644 index 00000000000..cfcc261906e --- /dev/null +++ b/libstdc++-v3/testsuite/26_numerics/random/random_device/94087.cc @@ -0,0 +1,63 @@ +// Copyright (C) 2020 Free Software Foundation, Inc. +// +// This file is part of the GNU ISO C++ Library. This library is free +// software; you can redistribute it and/or modify it under the +// terms of the GNU General Public License as published by the +// Free Software Foundation; either version 3, or (at your option) +// any later version. + +// This library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License along +// with this library; see the file COPYING3. If not see +// <http://www.gnu.org/licenses/>. + +// { dg-do run } +// { dg-options "-pthread" } +// { dg-require-effective-target c++11 } +// { dg-require-effective-target pthread } +// { dg-require-gthreads "" } + +#include <random> +#include <memory> +#include <thread> +#include <cstdio> + +bool +random_device_available(const char* token) noexcept +{ + try { + std::random_device dev(token); + return true; + } catch (...) { + std::printf("random_device(\"%s\") not available\n", token); + return false; + } +} + +void read_random_device(const char* token, int iterations) +{ + std::random_device dev(token); + for (int i = 0; i != iterations; ++i) + (void) dev(); +} + +int main() { + std::thread workers[8]; + + // N.B. don't test /dev/random as it might block, and /dev/urandom + // "can incur an appreciable delay when requesting large amounts of data". + for (const char* dev : { "default", "rdrand", "rdseed", "rand_s" }) + { + if (random_device_available(dev)) + { + for (auto& w : workers) + w = std::thread{read_random_device, dev, 1000}; + for (auto& w : workers) + w.join(); + } + } +}
reply other threads:[~2020-07-17 15:38 UTC|newest] Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20200717153851.2D7693945C2D@sourceware.org \ --to=tnfchris@gcc.gnu.org \ --cc=gcc-cvs@gcc.gnu.org \ --cc=libstdc++-cvs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).