cpu: detect RDRAND and RDSEED instructions on x86

Change-Id: I2d0094d64ba12f888758aeebdb43aed353ddeeb9
Reviewed-on: https://go-review.googlesource.com/c/160577
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

cpu/cpu.go

@@ -29,6 +29,8 @@ var X86 struct {
 	HasOSXSAVE   bool // OS supports XSAVE/XRESTOR for saving/restoring XMM registers.
 	HasPCLMULQDQ bool // PCLMULQDQ instruction - most often used for AES-GCM
 	HasPOPCNT    bool // Hamming weight instruction POPCNT.
+	HasRDRAND    bool // RDRAND instruction (on-chip random number generator)
+	HasRDSEED    bool // RDSEED instruction (on-chip random number generator)
 	HasSSE2      bool // Streaming SIMD extension 2 (always available on amd64)
 	HasSSE3      bool // Streaming SIMD extension 3
 	HasSSSE3     bool // Supplemental streaming SIMD extension 3

cpu/cpu_x86.go

@@ -27,6 +27,7 @@ func init() {
 	X86.HasPOPCNT = isSet(23, ecx1)
 	X86.HasAES = isSet(25, ecx1)
 	X86.HasOSXSAVE = isSet(27, ecx1)
+	X86.HasRDRAND = isSet(30, ecx1)
 
 	osSupportsAVX := false
 	// For XGETBV, OSXSAVE bit is required and sufficient.
@@ -47,6 +48,7 @@ func init() {
 	X86.HasAVX2 = isSet(5, ebx7) && osSupportsAVX
 	X86.HasBMI2 = isSet(8, ebx7)
 	X86.HasERMS = isSet(9, ebx7)
+	X86.HasRDSEED = isSet(18, ebx7)
 	X86.HasADX = isSet(19, ebx7)
 }