[PATCH] PR libstdc++/85494 use rdseed and rand_s in std::random_device

[Jonathan Wakely]

On 29/05/19 15:45 +0100, Jonathan Wakely wrote:
>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.

This fixes a test that started to fail in mingw.

Tested x86_64-linux, powerpc64le-linux and x86_64-w64-ming32.

Committed to trunk.


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