build bootloaders from code

This adds the infrastructure for building from source the bootloaders which
will go into the application initial program, in the boot sector.  As a
simple test case, it includes a simple bootloader which merely jumpts to
the code address specified in the AIP, with the stack address specified
there.

1 files changed, 55 insertions, 0 deletions

diff --git a/boot/bootloader.h b/boot/bootloader.h
new file mode 100644
index 0000000..e5c013d
--- /dev/null
+++ b/boot/bootloader.h
@@ -0,0 +1,55 @@
+#include "../src/bootinfo.h"
+
+/* to be provider by the bootloader including this header */
+_Noreturn void bootloader(struct systemid *boot);
+
+__asm__(
+".text \n"
+".extern __bss_start \n"
+".extern __bss_end \n"
+".global __start \n"
+".type __start, @function \n"
+"__start: \n"
+
+/* zero any bss section */
+"	mov #0, r0 \n"
+"	mov.l 1f, r1 \n"
+"	mov.l 2f, r2 \n"
+"0:	cmp/hi r1, r2 \n"
+"	bf 0f \n"
+"	bra 0b \n"
+"	 mov.l r0, @-r2 \n"
+
+/* cannibalize code before this for stack space, and pass control to C */
+"0:	mov.l 3f, r15 \n"
+"	mov.l 4f, r4 \n"
+"	bra bootloader \n"
+"	 nop \n"
+
+".align 2 \n"
+"1:	.long __bss_start \n"
+"2:	.long __bss_end \n"
+"3:	.long __start \n"
+"4:	.long 0x06002000 \n"
+);
+
+/* helper to jump to the specified code with the specified stack */
+static inline _Noreturn void jump(const void *code, long *stack)
+{
+	__asm__ __volatile__(
+		"	jmp @%0\n"
+		"	 mov %1, r15\n"
+		: : "r"(code), "r"(stack)
+	);
+	__builtin_unreachable();
+}
+
+/* helper to abort by repeatedly executing an illegal instruction */
+static inline _Noreturn void fail(void)
+{
+	__asm__ __volatile__(
+		"0:	bra 0b\n"
+		"	.word 0xfffd\n"
+	);
+	__builtin_unreachable();
+}