microwatt/hello_world/head.S

/* Copyright 2013-2014 IBM Corp.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * 	http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define STACK_TOP 0x2000

#define FIXUP_ENDIAN						   \
	tdi   0,0,0x48;	  /* Reverse endian of b . + 8		*/ \
	b     191f;	  /* Skip trampoline if endian is good	*/ \
	.long 0xa600607d; /* mfmsr r11				*/ \
	.long 0x01006b69; /* xori r11,r11,1			*/ \
	.long 0x05009f42; /* bcl 20,31,$+4			*/ \
	.long 0xa602487d; /* mflr r10				*/ \
	.long 0x14004a39; /* addi r10,r10,20			*/ \
	.long 0xa64b5a7d; /* mthsrr0 r10			*/ \
	.long 0xa64b7b7d; /* mthsrr1 r11			*/ \
	.long 0x2402004c; /* hrfid				*/ \
191:


/* Load an immediate 64-bit value into a register */
#define LOAD_IMM64(r, e)			\
	lis     r,(e)@highest;			\
	ori     r,r,(e)@higher;			\
	rldicr  r,r, 32, 31;			\
	oris    r,r, (e)@h;			\
	ori     r,r, (e)@l;

	.section ".head","ax"

	/*
	 * Microwatt currently enters in LE mode at 0x0, so we don't need to
	 * do any endian fix ups>
	 */
	. = 0
.global _start
_start:
	b	boot_entry

	/* QEMU enters at 0x10 */
	. = 0x10
	FIXUP_ENDIAN
	b	boot_entry

	. = 0x100
	FIXUP_ENDIAN
	b	boot_entry

.global boot_entry
boot_entry:
	/* setup stack */
	LOAD_IMM64(%r1, STACK_TOP - 0x100)
	LOAD_IMM64(%r12, main)
	mtctr	%r12,
	bctrl
	b .