Set fixed field in CPUID function 2

From the SDM: "The least-significant byte in register EAX (register AL)
will always return 01H. Software should ignore this value and not
interpret it as an informational descriptor."

Unfortunately, online docs [1] [2] (likely based on an old version of the SDM)
say: "The least-significant byte in register EAX (register AL) indicates
the number of times the CPUID instruction must be executed with an input
value of 2 to get a complete description of the processor's caches and
TLBs."

dlang uses this second interpretation [3] and will loop 2^32 times if we
return zero. Fix this by specifying the fixed value of one. We still
don't support exposing the actual cache information, leaving all other
bytes empty. A zero byte means: "Null descriptor, this byte contains no
information."

[1] http://www.sandpile.org/x86/cpuid.htm#level_0000_0002h
[2] https://c9x.me/x86/html/file_module_x86_id_45.html
[3] https://github.com/dlang/druntime/blob/424640864c2aa001731467e96f637bd3e704e481/src/core/cpuid.d#L533-L534

PiperOrigin-RevId: 242046629
Change-Id: Ic0f0a5f974b20f71391cb85645bdcd4003e5fe88

0 files changed, 0 insertions, 0 deletions