kernel: add per-cpu data section to kernel image

arch/x86_64/layout.ld

@@ -31,6 +31,13 @@ SECTIONS {
         *(.data)
    }
 
+   .data.percpu ALIGN(4K) : AT(ADDR(.data.percpu) - KERNEL_VMA)
+   {
+	__percpu_start = .;
+	*(.data.percpu)
+	__percpu_end = .;
+   }
+
    .initcall ALIGN(4K) : AT(ADDR(.initcall) - KERNEL_VMA) {
         __initcall0_start = .;
         *(.initcall0.init)

include/socks/cpu.h

@@ -0,0 +1,13 @@
+#ifndef SOCKS_CPU_H_
+#define SOCKS_CPU_H_
+
+#include <socks/bitmap.h>
+
+/* maximum number of processor cores that the kernel can support.
+   TODO move to build config option */
+#define CPU_MAX 128
+
+DECLARE_BITMAP(cpu_available, CPU_MAX);
+DECLARE_BITMAP(cpu_online, CPU_MAX);
+
+#endif

include/socks/percpu.h

@@ -0,0 +1,15 @@
+#ifndef SOCKS_PERCPU_H_
+#define SOCKS_PERCPU_H_
+
+#include <socks/compiler.h>
+
+#define DEFINE_PERCPU_VAR(type, name) \
+	__section(".data.percpu") type name
+
+#define percpu_get(var) __percpu_get(var)
+
+#define percpu_put(var)
+
+extern void *__percpu_get(void *var);
+
+#endif