kernel: implement cpu IDs and per-cpu variables

kernel/percpu.c

@@ -0,0 +1,40 @@
+#include <socks/percpu.h>
+#include <socks/cpu.h>
+#include <socks/vm.h>
+#include <stdint.h>
+#include <stddef.h>
+
+extern char __percpu_start[];
+extern char __percpu_end[];
+
+static void *percpu_buffer = NULL;
+static size_t percpu_stride = 0;
+
+extern kern_status_t init_per_cpu_areas(void)
+{
+	unsigned int last_cpu = cpu_get_highest_available();
+
+	percpu_stride = (uintptr_t)__percpu_end - (uintptr_t)__percpu_start;
+	if (percpu_stride & 0x7) {
+		percpu_stride &= ~0x7;
+		percpu_stride += 0x8;
+	}
+
+	percpu_buffer = kmalloc(last_cpu * percpu_stride, 0);
+	return KERN_OK;
+}
+
+extern void *__percpu_get(void *var)
+{
+	uintptr_t pvar = (uintptr_t)var;
+	uintptr_t percpu_start = (uintptr_t)__percpu_start;
+	uintptr_t percpu_end = (uintptr_t)__percpu_end;
+
+	if (pvar < percpu_start || pvar >= percpu_end) {
+		return NULL;
+	}
+
+	size_t var_offset = pvar - percpu_start;
+
+	return (char *)percpu_buffer + (this_cpu() * percpu_stride) + var_offset;
+}