x86_64: define struct offsets for access from assembly

arch/x86_64/asm-offset.c

@@ -0,0 +1,27 @@
+#include <socks/sched.h>
+#include <socks/compiler.h>
+
+//size_t THREAD_sp = offsetof(struct thread, tr_sp);
+
+/* Use %a0 instead of %0 to prevent gcc from emitting a $ before the symbol value
+   in the generated assembly.
+
+   emitting
+     .set TASK_sp, $56
+
+   instead of
+     .set TASK_sp, 56
+
+   causes garbage symbols to be generated.
+*/
+
+#define DEFINE(sym, val) \
+	asm volatile("\n.global " #sym "\n.type " #sym ", @object" "\n.set " #sym ", %a0" : : "i" (val))
+
+#define OFFSET(sym, str, mem) \
+	DEFINE(sym, offsetof(str, mem))
+
+static void __used common(void)
+{
+	OFFSET(THREAD_sp, struct thread, tr_sp);
+}