X runtime.GetCPU()

This way one can verify on which physical CPU the code is currently
running.

src/runtime/stubs_linux.go

@@ -7,3 +7,13 @@
 package runtime
 
 func sbrk0() uintptr
+func _getcpu() (cpu, node uint32, ret int32)
+
+func GetCPU() (cpu, node uint32) {
+	cpu, node, ret := _getcpu()
+	//println("_getcpu ->", cpu, node, ret)
+	if ret != 0 {
+		throw("getcpu failed")
+	}
+	return cpu, node
+}

src/runtime/sys_linux_amd64.s

@@ -45,6 +45,7 @@
 #define SYS_epoll_ctl		233
 #define SYS_pselect6		270
 #define SYS_epoll_create1	291
+#define SYS_getcpu		309
 
 TEXT runtime·exit(SB),NOSPLIT,$0-4
 	MOVL	code+0(FP), DI
@@ -659,3 +660,13 @@ TEXT runtime·sbrk0(SB),NOSPLIT,$0-8
 	SYSCALL
 	MOVQ	AX, ret+0(FP)
 	RET
+
+// func _getcpu() (cpu, node uint32, ret int32)
+TEXT runtime·_getcpu(SB),NOSPLIT,$0
+	LEAQ	cpu+0(FP), DI
+	LEAQ	node+4(FP), SI
+	XORQ	DX, DX		// tcache
+	MOVL	$SYS_getcpu, AX
+	SYSCALL
+	MOVL	AX, ret+8(FP)
+	RET