powerpc/boot: Modify entry point for 64bit

This patch adds support a 64bit wrapper entry point. As in 32bit, the
entry point does its own relocation and can be loaded at any address
by the firmware.

Signed-off-by: Cédric Le Goater <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/boot/crt0.S

···
 /*
  * Copyright (C) Paul Mackerras 1997.
  *
+ * Adapted for 64 bit LE PowerPC by Andrew Tauferner
+ *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
  * as published by the Free Software Foundation; either version
  * 2 of the License, or (at your option) any later version.
  *
- * NOTE: this code runs in 32 bit mode, is position-independent,
- * and is packaged as ELF32.
  */
 
 #include "ppc_asm.h"
+
+RELA = 7
+RELACOUNT = 0x6ffffff9
 
 	.text
 	/* A procedure descriptor used when booting this as a COFF file.
···
 _zimage_start_opd:
 	.long	0x500000, 0, 0, 0
 
+#ifdef __powerpc64__
+.balign 8
+p_start:	.llong	_start
+p_etext:	.llong	_etext
+p_bss_start:	.llong	__bss_start
+p_end:		.llong	_end
+
+p_toc:		.llong	__toc_start + 0x8000 - p_base
+p_dyn:		.llong	__dynamic_start - p_base
+p_rela:		.llong	__rela_dyn_start - p_base
+p_prom:		.llong	0
+	.weak	_platform_stack_top
+p_pstack:	.llong	_platform_stack_top
+#else
 p_start:	.long	_start
 p_etext:	.long	_etext
 p_bss_start:	.long	__bss_start
···
 
 	.weak	_platform_stack_top
 p_pstack:	.long	_platform_stack_top
+#endif
 
 	.weak	_zimage_start
 	.globl	_zimage_start
···
 	   and the address where we're running. */
 	bl	.+4
 p_base:	mflr	r10		/* r10 now points to runtime addr of p_base */
+#ifndef __powerpc64__
 	/* grab the link address of the dynamic section in r11 */
 	addis	r11,r10,(_GLOBAL_OFFSET_TABLE_-p_base)@ha
 	lwz	r11,(_GLOBAL_OFFSET_TABLE_-p_base)@l(r11)
···
 
 	/* The dynamic section contains a series of tagged entries.
 	 * We need the RELA and RELACOUNT entries. */
-RELA = 7
-RELACOUNT = 0x6ffffff9
 	li	r9,0
 	li	r0,0
 9:	lwz	r8,0(r12)	/* get tag */
···
 	li	r0,0
 	stwu	r0,-16(r1)	/* establish a stack frame */
 6:
+#else /* __powerpc64__ */
+	/* Save the prom pointer at p_prom. */
+	std	r5,(p_prom-p_base)(r10)
 
+	/* Set r2 to the TOC. */
+	ld	r2,(p_toc-p_base)(r10)
+	add	r2,r2,r10
+
+	/* Grab the link address of the dynamic section in r11. */
+	ld	r11,-32768(r2)
+	cmpwi	r11,0
+	beq	3f              /* if not linked -pie then no dynamic section */
+
+	ld	r11,(p_dyn-p_base)(r10)
+	add	r11,r11,r10
+	ld	r9,(p_rela-p_base)(r10)
+	add	r9,r9,r10
+
+	li	r7,0
+	li	r8,0
+9:	ld	r6,0(r11)       /* get tag */
+	cmpdi	r6,0
+	beq	12f              /* end of list */
+	cmpdi	r6,RELA
+	bne	10f
+	ld	r7,8(r11)       /* get RELA pointer in r7 */
+	b	11f
+10:	addis	r6,r6,(-RELACOUNT)@ha
+	cmpdi	r6,RELACOUNT@l
+	bne	11f
+	ld	r8,8(r11)       /* get RELACOUNT value in r8 */
+11:	addi	r11,r11,16
+	b	9b
+12:
+	cmpdi	r7,0            /* check we have both RELA and RELACOUNT */
+	cmpdi	cr1,r8,0
+	beq	3f
+	beq	cr1,3f
+
+	/* Calcuate the runtime offset. */
+	subf	r7,r7,r9
+
+	/* Run through the list of relocations and process the
+	 * R_PPC64_RELATIVE ones. */
+	mtctr	r8
+13:	ld	r0,8(r9)        /* ELF64_R_TYPE(reloc->r_info) */
+	cmpdi	r0,22           /* R_PPC64_RELATIVE */
+	bne	3f
+	ld	r6,0(r9)        /* reloc->r_offset */
+	ld	r0,16(r9)       /* reloc->r_addend */
+	add	r0,r0,r7
+	stdx	r0,r7,r6
+	addi	r9,r9,24
+	bdnz	13b
+
+	/* Do a cache flush for our text, in case the loader didn't */
+3:	ld	r9,p_start-p_base(r10)	/* note: these are relocated now */
+	ld	r8,p_etext-p_base(r10)
+4:	dcbf	r0,r9
+	icbi	r0,r9
+	addi	r9,r9,0x20
+	cmpld	cr0,r9,r8
+	blt	4b
+	sync
+	isync
+
+	/* Clear the BSS */
+	ld	r9,p_bss_start-p_base(r10)
+	ld	r8,p_end-p_base(r10)
+	li	r0,0
+5:	std	r0,0(r9)
+	addi	r9,r9,8
+	cmpld	cr0,r9,r8
+	blt	5b
+
+	/* Possibly set up a custom stack */
+	ld	r8,p_pstack-p_base(r10)
+	cmpdi	r8,0
+	beq	6f
+	ld	r1,0(r8)
+	li	r0,0
+	stdu	r0,-16(r1)	/* establish a stack frame */
+6:
+#endif  /* __powerpc64__ */
 	/* Call platform_init() */
 	bl	platform_init