[RFC PATCH] advapi32: Use Windows APIs to read /dev/urandom.

[Gabriel Ivăncescu]

On 04/09/2020 14:15, Hans Leidekker wrote:
> This will cause a performance regression. SystemFunction036 (RtlGenRandom)
> is already an order of magnitude slower than native because it opens and closes
> /dev/urandom on every call. Going through wineserver makes it 2 orders of
> magnitude slower:
> 
> int buf[4], i;
> for (i = 0; i < 100000; i++) RtlGenRandom(buf, sizeof(buf));
> 
> Windows:                      16 ticks
> Wine/open():                 209 ticks
> Wine/NtCreateFile():        3612 ticks
> Wine/NtCreateFile()/cached:   96 ticks
> 
> We could cache the file handle to mitigate that, but then there's the risk that
> an application accidentally closes the handle.
> 
> Ideally we'd implement this with getrandom() on Linux. We probably don't want
> to split advapi32 just for this, so maybe a private ntdll export is justified
> here?
> 

Another idea would be to use the Linux syscall directly, with inline 
asm, which should work from PE too. Right?

And if it's not present (e.g. old kernel), fallback to slow implementation.