[PATCH]std::random_device for win32 (MinGW) ABI implementation

[Jonathan Wakely]

On 12/10/18 17:45 +0000, sotrdg sotrdg wrote:
>The implementation is on the GitHub.
>
>https://github.com/euloanty/mingw-std-random_device/blob/master/random_device_gcc_withcxx11abi/random.cc
>
>
>This implementation does several changes towards the original random.cc.
>
>
>  1.  Type Erasure Abstractions for various random_devices so we can choose any of them to use if necessary.
>  2.  Solve security issue of setvbuf(fp,nullptr,_IONBF,0); In order to avoid seeds leaking to other processes after releasing the buffer of std::FILE*.
>  3.  For amd64 platform, random_device will prefer using rdseed instruction instead of rdrand instruction
>  4.  For Windows, random_device will get seeds from RtlGenRandom and buffer it.
>  5.  Legacy support for mt19937.
>I’ve put it on the GitHub for anyone.

Thanks for this, although I'm afraid we can't use it without some
additional steps being taken, see https://gcc.gnu.org/contribute.html#legal

However, as I mentioned at
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85494#c4 I've already
been working on an implementation that uses RtlGenRandom. My version
is attached. This implementation allows constructing a
std::random_device with the following tokens (where supported):

"default" - choose the first supported 
"rtlgenrandom" - use Windows RtlGenRandom
"rdrand" or "rdrnd" - use RDRAND instruction
"rdseed" - use RDSEED instruction
"/dev/urandom" or "/dev/random" - use specified device file

This should be an ABI compatible change, so that existing MinGW
applications don't need to be recompiled, they just need to use the
new libstdc++-6.dll to get the new implementation (although they won't
get the secure zeroing out of memory without a recompile).

I've only done minimal testing using a mingw-w64 cross-compile and
executing under Wine, but it seems to work well.

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