[GDB] Add GDB stub for remote debugging

See http://etherboot.org/wiki/dev/gdbstub for documentation.

src/arch/i386/include/gdbmach.h

@@ -0,0 +1,51 @@
+#ifndef GDBMACH_H
+#define GDBMACH_H
+
+/** @file
+ *
+ * GDB architecture specifics
+ *
+ * This file declares functions for manipulating the machine state and
+ * debugging context.
+ *
+ */
+
+typedef uint32_t gdbreg_t;
+
+/* The register snapshot, this must be in sync with interrupt handler and the
+ * GDB protocol. */
+enum {
+	GDBMACH_EAX,
+	GDBMACH_ECX,
+	GDBMACH_EDX,
+	GDBMACH_EBX,
+	GDBMACH_ESP,
+	GDBMACH_EBP,
+	GDBMACH_ESI,
+	GDBMACH_EDI,
+	GDBMACH_EIP,
+	GDBMACH_EFLAGS,
+	GDBMACH_CS,
+	GDBMACH_SS,
+	GDBMACH_DS,
+	GDBMACH_ES,
+	GDBMACH_FS,
+	GDBMACH_GS,
+	GDBMACH_NREGS,
+	GDBMACH_SIZEOF_REGS = GDBMACH_NREGS * sizeof ( gdbreg_t )
+};
+
+static inline void gdbmach_set_pc ( gdbreg_t *regs, gdbreg_t pc ) {
+	regs [ GDBMACH_EIP ] = pc;
+}
+
+static inline void gdbmach_set_single_step ( gdbreg_t *regs, int step ) {
+	regs [ GDBMACH_EFLAGS ] &= ~( 1 << 8 ); /* Trace Flag (TF) */
+	regs [ GDBMACH_EFLAGS ] |= ( step << 8 );
+}
+
+static inline void gdbmach_breakpoint ( void ) {
+	__asm__ __volatile__ ( "int $3\n" );
+}
+
+#endif /* GDBMACH_H */