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

[Jonathan Wakely]

On 29/05/19 23:03 +0100, Jonathan Wakely wrote:
>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.

I forgot that the random_device::_M_init member is duplicated in
src/c++11/cow-string-inst.cc for the old strings, so tests using the
old string now fail.

I'll try to find a better way to define those member functions for old
strings.