@@ -4053,6 +4053,26 @@ AC_DEFUN([GLIBCXX_CHECK_X86_RDRAND], [
AC_MSG_RESULT($ac_cv_x86_rdrand)
])
+dnl
+dnl Check whether rdseed is supported in the assembler.
+AC_DEFUN([GLIBCXX_CHECK_X86_RDSEED], [
+ AC_MSG_CHECKING([for rdseed support in assembler])
+ AC_CACHE_VAL(ac_cv_x86_rdseed, [
+ ac_cv_x86_rdseed=no
+ case "$target" in
+ i?86-*-* | \
+ x86_64-*-*)
+ AC_TRY_COMPILE(, [asm("rdseed %eax");],
+ [ac_cv_x86_rdseed=yes], [ac_cv_x86_rdseed=no])
+ esac
+ ])
+ if test $ac_cv_x86_rdseed = yes; then
+ AC_DEFINE(_GLIBCXX_X86_RDSEED, 1,
+ [ Defined if as can handle rdseed. ])
+ fi
+ AC_MSG_RESULT($ac_cv_x86_rdseed)
+])
+
dnl
dnl Check whether get_nprocs is available in <sys/sysinfo.h>, and define _GLIBCXX_USE_GET_NPROCS.
dnl
@@ -88,4 +88,6 @@
// See libstdc++/59807
#define _GTHREAD_USE_MUTEX_INIT_FUNC 1
+#define _GLIBCXX_USE_CRT_RAND_S 1
+
#endif
@@ -417,6 +417,8 @@ GCC_CHECK_ASSEMBLER_HWCAP
# Check if assembler supports rdrand opcode.
GLIBCXX_CHECK_X86_RDRAND
+# Check if assembler supports rdseed opcode.
+GLIBCXX_CHECK_X86_RDSEED
# This depends on GLIBCXX_ENABLE_SYMVERS and GLIBCXX_IS_NATIVE.
GLIBCXX_CONFIGURE_TESTSUITE
@@ -2682,18 +2682,62 @@ particular release.
<para>
<emphasis> 26.5.6 [rand.device] </emphasis>
- The default <code>token</code> argument to the
- <classname>random_device</classname> constructor is
- <literal>"default"</literal>. Other valid arguments are
- <literal>"/dev/random"</literal> and <literal>"/dev/urandom"</literal>,
- which determine the character special file to read random bytes from.
- The <literal>"default"</literal> token will read bytes from a hardware
- RNG if available (currently this only supports the IA-32 RDRAND
- instruction) otherwise it is equivalent to
- <literal>"/dev/urandom"</literal>.
+ The <code>token</code> parameter of the
+ <classname>random_device</classname> constructor can be used to select
+ a specific source of random bytes. The valid token values are shown
+ in the list below.
+ The default constructor uses the token <literal>"default"</literal>.
+ <variablelist>
+ <varlistentry>
+ <term><literal>"default"</literal></term>
+ <listitem>
+ Select the first available source from the other entries below.
+ This is the only token that is always valid.
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>"rand_s"</literal></term>
+ <listitem>
+ Use the MSVCRT <function>rand_s</function> function.
+ This token is only valid for mingw-w64 targets.
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>"rdseed"</literal></term>
+ <term><literal>"rdrand"</literal> or <literal>"rdrnd"</literal></term>
+ <listitem>
+ Use the IA-32 <literal>RDSEED</literal> or <literal>RDRAND</literal>
+ instruction to read from an on-chip hardware random number generator.
+ These tokens are only valid for x86 and x86_64 targets when both
+ the assembler and CPU support the corresponding instruction.
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>"/dev/urandom"</literal></term>
+ <term><literal>"/dev/random"</literal></term>
+ <listitem>
+ Use the named character special file to read random bytes from.
+ These tokens are only valid when the device files are present
+ and readable by the current user.
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>"mt19937"</literal></term>
+ <term>seed value</term>
+ <listitem>
+ When no source of nondeterministic random numbers is available a
+ <classname>mersenne_twister_engine</classname> will be used.
+ An integer seed value can be used as the token and will be converted
+ to an <code>unsigned long</code> using <function>strtoul</function>.
+ These tokens are only valid when no other source of random bytes
+ is available.
+ </listitem>
+ </varlistentry>
+ </variablelist>
An exception of type <classname>runtime_error</classname> will be
- thrown if a <classname>random_device</classname> object cannot open
- or read from the source of random bytes.
+ thrown if a <classname>random_device</classname> object is constructed
+ with an invalid token, or if it cannot open or read from the source
+ of random bytes.
</para>
<para>
@@ -1602,20 +1602,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// constructors, destructors and member functions
-#ifdef _GLIBCXX_USE_DEV_RANDOM
random_device() { _M_init("default"); }
explicit
random_device(const std::string& __token) { _M_init(__token); }
+#if defined _GLIBCXX_USE_DEV_RANDOM
~random_device()
{ _M_fini(); }
-#else
- random_device() { _M_init_pretr1("mt19937"); }
-
- explicit
- random_device(const std::string& __token)
- { _M_init_pretr1(__token); }
#endif
static constexpr result_type
@@ -1638,13 +1632,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
result_type
operator()()
- {
-#ifdef _GLIBCXX_USE_DEV_RANDOM
- return this->_M_getval();
-#else
- return this->_M_getval_pretr1();
-#endif
- }
+ { return this->_M_getval(); }
// No copy functions.
random_device(const random_device&) = delete;
@@ -1662,7 +1650,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
union
{
- void* _M_file;
+ struct
+ {
+ void* _M_file;
+ result_type (*_M_func)(void*);
+ int _M_fd;
+ };
mt19937 _M_mt;
};
};
@@ -23,19 +23,30 @@
// <http://www.gnu.org/licenses/>.
#define _GLIBCXX_USE_CXX11_ABI 1
+#define _CRT_RAND_S // define this before including <stdlib.h> to get rand_s
+
#include <random>
#ifdef _GLIBCXX_USE_C99_STDINT_TR1
#if defined __i386__ || defined __x86_64__
# include <cpuid.h>
+# ifdef _GLIBCXX_X86_RDRAND
+# define USE_RDRAND 1
+# endif
+# ifdef _GLIBCXX_X86_RDSEED
+# define USE_RDSEED 1
+# endif
#endif
#include <cerrno>
#include <cstdio>
-#ifdef _GLIBCXX_HAVE_UNISTD_H
+#if defined _GLIBCXX_HAVE_UNISTD_H && defined _GLIBCXX_HAVE_FCNTL_H
# include <unistd.h>
+# include <fcntl.h>
+// Use POSIX open, close, read etc. instead of ISO fopen, fclose, fread
+# define USE_POSIX_FILE_IO
#endif
#ifdef _GLIBCXX_HAVE_SYS_IOCTL_H
@@ -50,105 +61,273 @@
# include <linux/random.h>
#endif
+#ifdef _GLIBCXX_USE_CRT_RAND_S
+# include <stdlib.h>
+#endif
+
+#if defined USE_RDRAND || defined USE_RDSEED \
+ || defined _GLIBCXX_USE_CRT_RAND_S || defined _GLIBCXX_USE_DEV_RANDOM
+# pragma GCC poison _M_mt
+#else
+// Use the mt19937 member of the union, as in previous GCC releases.
+# define USE_MT19937 1
+#endif
+
namespace std _GLIBCXX_VISIBILITY(default)
{
namespace
{
- static unsigned long
- _M_strtoul(const std::string& __str)
- {
- unsigned long __ret = 5489UL;
- if (__str != "mt19937")
- {
- const char* __nptr = __str.c_str();
- char* __endptr;
- __ret = std::strtoul(__nptr, &__endptr, 0);
- if (*__nptr == '\0' || *__endptr != '\0')
- std::__throw_runtime_error(__N("random_device::_M_strtoul"
- "(const std::string&)"));
- }
- return __ret;
- }
-
-#if (defined __i386__ || defined __x86_64__) && defined _GLIBCXX_X86_RDRAND
+#if USE_RDRAND
unsigned int
__attribute__ ((target("rdrnd")))
- __x86_rdrand(void)
+ __x86_rdrand(void*)
{
unsigned int retries = 100;
unsigned int val;
while (__builtin_ia32_rdrand32_step(&val) == 0)
if (--retries == 0)
- std::__throw_runtime_error(__N("random_device::__x86_rdrand(void)"));
+ std::__throw_runtime_error(__N("random_device: rdrand failed"));
return val;
}
#endif
+
+#if USE_RDSEED
+ unsigned int
+ __attribute__ ((target("rdseed")))
+ __x86_rdseed(void*)
+ {
+ unsigned int retries = 100;
+ unsigned int val;
+
+ while (__builtin_ia32_rdseed_si_step(&val) == 0)
+ {
+ if (--retries == 0)
+ std::__throw_runtime_error(__N("random_device: rdseed failed"));
+ __builtin_ia32_pause();
+ }
+
+ return val;
+ }
+#endif
+
+#ifdef _GLIBCXX_USE_CRT_RAND_S
+ unsigned int
+ __winxp_rand_s(void*)
+ {
+ unsigned int val;
+ if (::rand_s(&val) != 0)
+ std::__throw_runtime_error(__N("random_device: rand_s failed"));
+ return val;
+ }
+#endif
}
void
random_device::_M_init(const std::string& token)
{
- const char *fname = token.c_str();
+#ifdef USE_MT19937
+ // If no real random device is supported then use the mt19937 engine.
+ _M_init_pretr1(token);
+ return;
+#else
+
+ _M_file = nullptr;
+ _M_func = nullptr;
+ _M_fd = -1;
+
+ const char* fname [[gnu::unused]] = nullptr;
+ bool default_token [[gnu::unused]] = false;
+
+ enum { rand_s, rdseed, rdrand, device_file } which;
if (token == "default")
{
-#if (defined __i386__ || defined __x86_64__) && defined _GLIBCXX_X86_RDRAND
+ default_token = true;
+ fname = "/dev/urandom";
+#if defined _GLIBCXX_USE_CRT_RAND_S
+ which = rand_s;
+#elif defined USE_RDSEED
+ which = rdseed;
+#elif defined USE_RDRAND
+ which = rdrand;
+#elif defined _GLIBCXX_USE_DEV_RANDOM
+ which = device_file;
+#else
+# error "either define USE_MT19937 above or set the default device here"
+#endif
+ }
+#ifdef USE_RDSEED
+ else if (token == "rdseed")
+ which = rdseed;
+#endif // USE_RDSEED
+#ifdef USE_RDRAND
+ else if (token == "rdrand" || token == "rdrnd")
+ which = rdrand;
+#endif // USE_RDRAND
+#ifdef _GLIBCXX_USE_CRT_RAND_S
+ else if (token == "rand_s")
+ which = rand_s;
+#endif // _GLIBCXX_USE_CRT_RAND_S
+#ifdef _GLIBCXX_USE_DEV_RANDOM
+ else if (token == "/dev/urandom" || token == "/dev/random")
+ {
+ fname = token.c_str();
+ which = device_file;
+ }
+#endif // _GLIBCXX_USE_DEV_RANDOM
+ else
+ std::__throw_runtime_error(
+ __N("random_device::random_device(const std::string&):"
+ " unsupported token"));
+
+ switch (which)
+ {
+#ifdef _GLIBCXX_USE_CRT_RAND_S
+ case rand_s:
+ {
+ _M_func = &__winxp_rand_s;
+ return;
+ }
+#endif // _GLIBCXX_USE_CRT_RAND_S
+#ifdef USE_RDSEED
+ case rdseed:
+ {
unsigned int eax, ebx, ecx, edx;
// Check availability of cpuid and, for now at least, also the
- // CPU signature for Intel's
- if (__get_cpuid_max(0, &ebx) > 0 && ebx == signature_INTEL_ebx)
+ // CPU signature for Intel and AMD.
+ if (__get_cpuid_max(0, &ebx) > 0
+ && (ebx == signature_INTEL_ebx || ebx == signature_AMD_ebx))
{
- __cpuid(1, eax, ebx, ecx, edx);
- if (ecx & bit_RDRND)
+ // CPUID.(EAX=07H, ECX=0H):EBX.RDSEED[bit 18]
+ __cpuid_count(7, 0, eax, ebx, ecx, edx);
+ if (ebx & bit_RDSEED)
{
- _M_file = nullptr;
+ _M_func = &__x86_rdseed;
return;
}
}
-#endif
-
- fname = "/dev/urandom";
+ // If rdseed was explicitly requested then we're done here.
+ if (!default_token)
+ break;
+ // Otherwise fall through to try the next available option.
+ [[gnu::fallthrough]];
}
- else if (token != "/dev/urandom" && token != "/dev/random")
- fail:
- std::__throw_runtime_error(__N("random_device::"
- "random_device(const std::string&)"));
-
- _M_file = static_cast<void*>(std::fopen(fname, "rb"));
- if (!_M_file)
- goto fail;
+#endif // USE_RDSEED
+#ifdef USE_RDRAND
+ case rdrand:
+ {
+ unsigned int eax, ebx, ecx, edx;
+ // Check availability of cpuid and, for now at least, also the
+ // CPU signature for Intel and AMD.
+ if (__get_cpuid_max(0, &ebx) > 0
+ && (ebx == signature_INTEL_ebx || ebx == signature_AMD_ebx))
+ {
+ // CPUID.01H:ECX.RDRAND[bit 30]
+ __cpuid(1, eax, ebx, ecx, edx);
+ if (ecx & bit_RDRND)
+ {
+ _M_func = &__x86_rdrand;
+ return;
+ }
+ }
+ // If rdrand was explicitly requested then we're done here.
+ if (!default_token)
+ break;
+ // Otherwise fall through to try the next available option.
+ [[gnu::fallthrough]];
+ }
+#endif // USE_RDRAND
+#ifdef _GLIBCXX_USE_DEV_RANDOM
+ case device_file:
+ {
+#ifdef USE_POSIX_FILE_IO
+ _M_fd = ::open(fname, O_RDONLY);
+ if (_M_fd != -1)
+ {
+ // Set _M_file to non-null so that _M_fini() will do clean up.
+ _M_file = &_M_fd;
+ return;
+ }
+#else // USE_POSIX_FILE_IO
+ _M_file = static_cast<void*>(std::fopen(fname, "rb"));
+ if (_M_file)
+ return;
+#endif // USE_POSIX_FILE_IO
+ [[gnu::fallthrough]];
+ }
+#endif // _GLIBCXX_USE_DEV_RANDOM
+ default:
+ { }
+ }
+ std::__throw_runtime_error(
+ __N("random_device::random_device(const std::string&):"
+ " device not available"));
+#endif // USE_MT19937
}
+ // This function is called by _M_init for targets that use mt19937 for
+ // randomness, and by code compiled against old releases of libstdc++.
void
random_device::_M_init_pretr1(const std::string& token)
{
- _M_mt.seed(_M_strtoul(token));
+#ifdef USE_MT19937
+ unsigned long seed = 5489UL;
+ if (token != "default" && token != "mt19937")
+ {
+ const char* nptr = token.c_str();
+ char* endptr;
+ seed = std::strtoul(nptr, &endptr, 0);
+ if (*nptr == '\0' || *endptr != '\0')
+ std::__throw_runtime_error(__N("random_device::_M_init_pretr1"
+ "(const std::string&)"));
+ }
+ _M_mt.seed(seed);
+#else
+ // Convert old default token "mt19937" or numeric seed tokens to "default".
+ if (token == "mt19937" || isdigit((unsigned char)token[0]))
+ _M_init("default");
+ else
+ _M_init(token);
+#endif
}
void
random_device::_M_fini()
{
- if (_M_file)
- std::fclose(static_cast<FILE*>(_M_file));
+ // _M_file == nullptr means no resources to free.
+ if (!_M_file)
+ return;
+
+#ifdef USE_POSIX_FILE_IO
+ ::close(_M_fd);
+ _M_fd = -1;
+#else
+ std::fclose(static_cast<FILE*>(_M_file));
+#endif
+ _M_file = nullptr;
}
random_device::result_type
random_device::_M_getval()
{
-#if (defined __i386__ || defined __x86_64__) && defined _GLIBCXX_X86_RDRAND
- if (!_M_file)
- return __x86_rdrand();
+#ifdef USE_MT19937
+ return _M_mt();
+#else
+
+#if defined USE_RDRAND || defined USE_RDSEED || defined _GLIBCXX_USE_CRT_RAND_S
+ if (_M_func)
+ return _M_func(nullptr);
#endif
- result_type __ret;
- void* p = &__ret;
+ result_type ret;
+ void* p = &ret;
size_t n = sizeof(result_type);
-#ifdef _GLIBCXX_HAVE_UNISTD_H
+#ifdef USE_POSIX_FILE_IO
do
{
- const int e = read(fileno(static_cast<FILE*>(_M_file)), p, n);
+ const int e = ::read(_M_fd, p, n);
if (e > 0)
{
n -= e;
@@ -158,34 +337,40 @@ namespace std _GLIBCXX_VISIBILITY(default)
__throw_runtime_error(__N("random_device could not be read"));
}
while (n > 0);
-#else
+#else // USE_POSIX_FILE_IO
const size_t e = std::fread(p, n, 1, static_cast<FILE*>(_M_file));
if (e != 1)
__throw_runtime_error(__N("random_device could not be read"));
-#endif
+#endif // USE_POSIX_FILE_IO
- return __ret;
+ return ret;
+#endif // USE_MT19937
}
+ // Only called by code compiled against old releases of libstdc++.
+ // Forward the call to _M_getval() and let it decide what to do.
random_device::result_type
random_device::_M_getval_pretr1()
- {
- return _M_mt();
- }
+ { return _M_getval(); }
double
random_device::_M_getentropy() const noexcept
{
-#if defined _GLIBCXX_HAVE_SYS_IOCTL_H && defined RNDGETENTCNT
+#if defined _GLIBCXX_USE_DEV_RANDOM \
+ && defined _GLIBCXX_HAVE_SYS_IOCTL_H && defined RNDGETENTCNT
if (!_M_file)
return 0.0;
- const int fd = fileno(static_cast<FILE*>(_M_file));
+#ifdef USE_POSIX_FILE_IO
+ const int fd = _M_fd;
+#else
+ const int fd = ::fileno(static_cast<FILE*>(_M_file));
+#endif
if (fd < 0)
return 0.0;
int ent;
- if (ioctl(fd, RNDGETENTCNT, &ent) < 0)
+ if (::ioctl(fd, RNDGETENTCNT, &ent) < 0)
return 0.0;
if (ent < 0)
@@ -198,9 +383,10 @@ namespace std _GLIBCXX_VISIBILITY(default)
return static_cast<double>(ent);
#else
return 0.0;
-#endif
+#endif // _GLIBCXX_USE_DEV_RANDOM && _GLIBCXX_HAVE_SYS_IOCTL_H && RNDGETENTCNT
}
+#ifdef USE_MT19937
template class mersenne_twister_engine<
uint_fast32_t,
32, 624, 397, 31,
@@ -208,5 +394,6 @@ namespace std _GLIBCXX_VISIBILITY(default)
0xffffffffUL, 7,
0x9d2c5680UL, 15,
0xefc60000UL, 18, 1812433253UL>;
+#endif // USE_MT19937
}
-#endif
+#endif // _GLIBCXX_USE_C99_STDINT_TR1
new file mode 100644
@@ -0,0 +1,40 @@
+// Copyright (C) 2019 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 { target c++11 } }
+// { dg-require-effective-target random_device }
+
+#include <random>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+ unsigned v1[3], v2[3];
+ std::random_device d1, d2;
+ for (auto& v : v1)
+ v = d1();
+ for (auto& v : v2)
+ v = d2();
+ VERIFY (v1[0] != v2[0] || v1[1] != v2[1] || v1[2] != v2[2] );
+}
+
+int
+main()
+{
+ test01();
+}
Add support for additional sources of randomness to std::random_device, to allow using RDSEED for Intel CPUs and rand_s for Windows. When supported these can be selected using the tokens "rdseed" and "rand_s". For *-w64-mingw32 targets the "default" token will now use rand_s, and for other i?86-*-* and x86_64-*-* targets it will try to use "rdseed" first, then "rdrand", and finally "/dev/urandom". To simplify the declaration of std::random_device in <bits/random.h> the constructors now unconditionally call _M_init instead of _M_init_pretr1, and the function call operator now unconditionally calls _M_getval. The library code now decides whether _M_init and _M_getval should use a real source of randomness or the mt19937 engine. Existing code compiled against old libstdc++ headers will still call _M_init_pretr1 and _M_getval_pretr1, but those functions now forward to _M_init and _M_getval if a real source of randomness is available. This means existing code compiled for mingw-w64 will start to use rand_s just by linking to a new libstdc++.dll. * acinclude.m4 (GLIBCXX_CHECK_X86_RDSEED): Define macro to check if the assembler supports rdseed. * config.h.in: Regenerate. * configure: Regenerate. * configure.ac: Use GLIBCXX_CHECK_X86_RDSEED. * config/os/mingw32-w64/os_defines.h (_GLIBCXX_USE_CRT_RAND_S): Define. * doc/html/*: Regenerate. * doc/xml/manual/status_cxx2011.xml: Document new tokens. * include/bits/random.h (random_device::random_device()): Always call _M_init rather than _M_init_pretr1. (random_device::random_device(const string&)): Likewise. (random_device::operator()()): Always call _M_getval(). (random_device::_M_file): Replace first member of union with an anonymous struct, with _M_file as its first member. * src/c++11/random.cc [_GLIBCXX_X86_RDRAND] (USE_RDRAND): Define. [_GLIBCXX_X86_RDSEED] (USE_RDSEED): Define. (USE_MT19937): Define if none of the above are defined. (USE_POSIX_FILE_IO): Define. (_M_strtoul): Remove. [USE_RDSEED] (__x86_rdseed): Define new function. [_GLIBCXX_USE_CRT_RAND_S] (__winxp_rand_s): Define new function. (random_device::_M_init(const string&)): Initialize new union members. Add support for "rdseed" and "rand_s" tokens. Decide what the "default" token does according to which USE_* macros are defined. [USE_POSIX_FILE_IO]: Store a file descriptor. [USE_MT19937]: Forward to _M_init_pretr1 instead. (random_device::_M_init_pretr1(const string&)) [USE_MT19937]: Inline code from _M_strtoul. [!USE_MT19937]: Call _M_init, transforming the old default token or numeric tokens to "default". (random_device::_M_fini()) [USE_POSIX_FILE_IO]: Use close not fclose. (random_device::_M_getval()): Use new union members to obtain a random number from the stored function pointer or file descriptor. [USE_MT19937]: Obtain a value from the mt19937 engine. (random_device::_M_getval_pretr1()): Call _M_getval(). (random_device::_M_getentropy()) [USE_POSIX_FILE_IO]: Use _M_fd instead of fileno. [!USE_MT19937] (mersenne_twister): Do not instantiate when not needed. * testsuite/26_numerics/random/random_device/85494.cc: New test. Tested x86_64-linux, powerpc64le-linux and x86_64-w64-ming32. Committed to trunk. commit dc337c84a7db52035f6b6efb87338e950bb7490e Author: Jonathan Wakely <jwakely@redhat.com> Date: Tue May 28 15:01:08 2019 +0100 PR libstdc++/85494 use rdseed and rand_s in std::random_device Add support for additional sources of randomness to std::random_device, to allow using RDSEED for Intel CPUs and rand_s for Windows. When supported these can be selected using the tokens "rdseed" and "rand_s". For *-w64-mingw32 targets the "default" token will now use rand_s, and for other i?86-*-* and x86_64-*-* targets it will try to use "rdseed" first, then "rdrand", and finally "/dev/urandom". To simplify the declaration of std::random_device in <bits/random.h> the constructors now unconditionally call _M_init instead of _M_init_pretr1, and the function call operator now unconditionally calls _M_getval. The library code now decides whether _M_init and _M_getval should use a real source of randomness or the mt19937 engine. Existing code compiled against old libstdc++ headers will still call _M_init_pretr1 and _M_getval_pretr1, but those functions now forward to _M_init and _M_getval if a real source of randomness is available. This means existing code compiled for mingw-w64 will start to use rand_s just by linking to a new libstdc++.dll. * acinclude.m4 (GLIBCXX_CHECK_X86_RDSEED): Define macro to check if the assembler supports rdseed. * config.h.in: Regenerate. * configure: Regenerate. * configure.ac: Use GLIBCXX_CHECK_X86_RDSEED. * config/os/mingw32-w64/os_defines.h (_GLIBCXX_USE_CRT_RAND_S): Define. * doc/html/*: Regenerate. * doc/xml/manual/status_cxx2011.xml: Document new tokens. * include/bits/random.h (random_device::random_device()): Always call _M_init rather than _M_init_pretr1. (random_device::random_device(const string&)): Likewise. (random_device::operator()()): Always call _M_getval(). (random_device::_M_file): Replace first member of union with an anonymous struct, with _M_file as its first member. * src/c++11/random.cc [_GLIBCXX_X86_RDRAND] (USE_RDRAND): Define. [_GLIBCXX_X86_RDSEED] (USE_RDSEED): Define. (USE_MT19937): Define if none of the above are defined. (USE_POSIX_FILE_IO): Define. (_M_strtoul): Remove. [USE_RDSEED] (__x86_rdseed): Define new function. [_GLIBCXX_USE_CRT_RAND_S] (__winxp_rand_s): Define new function. (random_device::_M_init(const string&)): Initialize new union members. Add support for "rdseed" and "rand_s" tokens. Decide what the "default" token does according to which USE_* macros are defined. [USE_POSIX_FILE_IO]: Store a file descriptor. [USE_MT19937]: Forward to _M_init_pretr1 instead. (random_device::_M_init_pretr1(const string&)) [USE_MT19937]: Inline code from _M_strtoul. [!USE_MT19937]: Call _M_init, transforming the old default token or numeric tokens to "default". (random_device::_M_fini()) [USE_POSIX_FILE_IO]: Use close not fclose. (random_device::_M_getval()): Use new union members to obtain a random number from the stored function pointer or file descriptor. [USE_MT19937]: Obtain a value from the mt19937 engine. (random_device::_M_getval_pretr1()): Call _M_getval(). (random_device::_M_getentropy()) [USE_POSIX_FILE_IO]: Use _M_fd instead of fileno. [!USE_MT19937] (mersenne_twister): Do not instantiate when not needed. * testsuite/26_numerics/random/random_device/85494.cc: New test.