Support the CPUID instruction

src/gopheros/kernel/cpu/cpu_amd64.go

@@ -1,5 +1,9 @@
 package cpu
 
+var (
+	cpuidFn = ID
+)
+
 // EnableInterrupts enables interrupt handling.
 func EnableInterrupts()
 
@@ -21,3 +25,16 @@ func ActivePDT() uintptr
 
 // ReadCR2 returns the value stored in the CR2 register.
 func ReadCR2() uint64
+
+// ID returns information about the CPU and its features. It
+// is implemented as a CPUID instruction with EAX=leaf and
+// returns the values in EAX, EBX, ECX and EDX.
+func ID(leaf uint32) (uint32, uint32, uint32, uint32)
+
+// IsIntel returns true if the code is running on an Intel processor.
+func IsIntel() bool {
+	_, ebx, ecx, edx := cpuidFn(0)
+	return ebx == 0x756e6547 && // "Genu"
+		edx == 0x49656e69 && // "ineI"
+		ecx == 0x6c65746e // "ntel"
+}

src/gopheros/kernel/cpu/cpu_amd64.s

@@ -31,3 +31,12 @@ TEXT ·ReadCR2(SB),NOSPLIT,$0
 	MOVQ CR2, AX
 	MOVQ AX, ret+0(FP)
 	RET
+
+TEXT ·ID(SB),NOSPLIT,$0
+	MOVQ leaf+0(FP), AX
+	CPUID
+	MOVL AX, ret+0(FP)
+	MOVL BX, ret+4(FP)
+	MOVL CX, ret+8(FP)
+	MOVL DX, ret+12(FP)
+	RET

src/gopheros/kernel/cpu/cpu_amd64_test.go

@@ -0,0 +1,29 @@
+package cpu
+
+import "testing"
+
+func TestIsIntel(t *testing.T) {
+	defer func() {
+		cpuidFn = ID
+	}()
+
+	specs := []struct {
+		eax, ebx, ecx, edx uint32
+		exp                bool
+	}{
+		// CPUID output from an Intel CPU
+		{0xd, 0x756e6547, 0x6c65746e, 0x49656e69, true},
+		// CPUID output from an AMD Athlon CPU
+		{0x1, 68747541, 0x444d4163, 0x69746e65, false},
+	}
+
+	for specIndex, spec := range specs {
+		cpuidFn = func(_ uint32) (uint32, uint32, uint32, uint32) {
+			return spec.eax, spec.ebx, spec.ecx, spec.edx
+		}
+
+		if got := IsIntel(); got != spec.exp {
+			t.Errorf("[spec %d] expected IsIntel to return %t; got %t", specIndex, spec.exp, got)
+		}
+	}
+}