Commit 6975a783 authored by Michael Ellerman's avatar Michael Ellerman Committed by Benjamin Herrenschmidt
Browse files

powerpc/boot: Allow building the zImage wrapper as a relocatable ET_DYN 



This patch adds code, linker script and makefile support to allow
building the zImage wrapper around the kernel as a position independent
executable.  This results in an ET_DYN instead of an ET_EXEC ELF output
file, which can be loaded at any location by the firmware and will
process its own relocations to work correctly at the loaded address.

This is of interest particularly since the standard ePAPR image format
must be an ET_DYN (although this patch alone is not sufficient to
produce a fully ePAPR compliant boot image).

Note for now we don't enable building with -pie for anything.

Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
Signed-off-by: default avatarDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: default avatarMichael Ellerman <michael@ellerman.id.au>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent ee7a2aa3

arch/powerpc/boot/crt0.S

+74 −42
Original line number Diff line number Diff line
@@ -6,16 +6,28 @@ 
 * 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 and is packaged as ELF32.

 * NOTE: this code runs in 32 bit mode, is position-independent,

 * and is packaged as ELF32.

 */



#include "ppc_asm.h"



	.text

	/* a procedure descriptor used when booting this as a COFF file */

	/* A procedure descriptor used when booting this as a COFF file.

	 * When making COFF, this comes first in the link and we're

	 * linked at 0x500000.

	 */

	.globl	_zimage_start_opd

_zimage_start_opd:

	.long	_zimage_start, 0, 0, 0

	.long	0x500000, 0, 0, 0



p_start:	.long	_start

p_etext:	.long	_etext

p_bss_start:	.long	__bss_start

p_end:		.long	_end



	.weak	_platform_stack_top

p_pstack:	.long	_platform_stack_top



	.weak	_zimage_start

	.globl	_zimage_start
@@ -24,37 +36,65 @@ _zimage_start: 
_zimage_start_lib:

	/* Work out the offset between the address we were linked at

	   and the address where we're running. */

	bl	1f

1:	mflr	r0

	lis	r9,1b@ha

	addi	r9,r9,1b@l

	subf.	r0,r9,r0

	beq	3f		/* if running at same address as linked */

	bl	.+4

p_base:	mflr	r10		/* r10 now points to runtime addr of p_base */

	/* 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)

	cmpwi	r11,0

	beq	3f		/* if not linked -pie */

	/* get the runtime address of the dynamic section in r12 */

	.weak	__dynamic_start

	addis	r12,r10,(__dynamic_start-p_base)@ha

	addi	r12,r12,(__dynamic_start-p_base)@l

	subf	r11,r11,r12	/* runtime - linktime offset */



	/* 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 */

	cmpwi	r8,0

	beq	10f		/* end of list */

	cmpwi	r8,RELA

	bne	11f

	lwz	r9,4(r12)	/* get RELA pointer in r9 */

	b	12f

11:	addis	r8,r8,(-RELACOUNT)@ha

	cmpwi	r8,RELACOUNT@l

	bne	12f

	lwz	r0,4(r12)	/* get RELACOUNT value in r0 */

12:	addi	r12,r12,8

	b	9b



	/* The .got2 section contains a list of addresses, so add

	   the address offset onto each entry. */

	lis	r9,__got2_start@ha

	addi	r9,r9,__got2_start@l

	lis	r8,__got2_end@ha

	addi	r8,r8,__got2_end@l

	subf.	r8,r9,r8

	/* The relocation section contains a list of relocations.

	 * We now do the R_PPC_RELATIVE ones, which point to words

	 * which need to be initialized with addend + offset.

	 * The R_PPC_RELATIVE ones come first and there are RELACOUNT

	 * of them. */

10:	/* skip relocation if we don't have both */

	cmpwi	r0,0

	beq	3f

	srwi.	r8,r8,2

	mtctr	r8

	add	r9,r0,r9

2:	lwz	r8,0(r9)

	add	r8,r8,r0

	stw	r8,0(r9)

	addi	r9,r9,4

	cmpwi	r9,0

	beq	3f



	add	r9,r9,r11	/* Relocate RELA pointer */

	mtctr	r0

2:	lbz	r0,4+3(r9)	/* ELF32_R_INFO(reloc->r_info) */

	cmpwi	r0,22		/* R_PPC_RELATIVE */

	bne	3f

	lwz	r12,0(r9)	/* reloc->r_offset */

	lwz	r0,8(r9)	/* reloc->r_addend */

	add	r0,r0,r11

	stwx	r0,r11,r12

	addi	r9,r9,12

	bdnz	2b



	/* Do a cache flush for our text, in case the loader didn't */

3:	lis	r9,_start@ha

	addi	r9,r9,_start@l

	add	r9,r0,r9

	lis	r8,_etext@ha

	addi	r8,r8,_etext@l

	add	r8,r0,r8

3:	lwz	r9,p_start-p_base(r10)	/* note: these are relocated now */

	lwz	r8,p_etext-p_base(r10)

4:	dcbf	r0,r9

	icbi	r0,r9

	addi	r9,r9,0x20
@@ -64,27 +104,19 @@ _zimage_start_lib: 
	isync



	/* Clear the BSS */

	lis	r9,__bss_start@ha

	addi	r9,r9,__bss_start@l

	add	r9,r0,r9

	lis	r8,_end@ha

	addi	r8,r8,_end@l

	add	r8,r0,r8

	li	r10,0

5:	stw	r10,0(r9)

	lwz	r9,p_bss_start-p_base(r10)

	lwz	r8,p_end-p_base(r10)

	li	r0,0

5:	stw	r0,0(r9)

	addi	r9,r9,4

	cmplw	cr0,r9,r8

	blt	5b



	/* Possibly set up a custom stack */

.weak	_platform_stack_top

	lis	r8,_platform_stack_top@ha

	addi	r8,r8,_platform_stack_top@l

	lwz	r8,p_pstack-p_base(r10)

	cmpwi	r8,0

	beq	6f

	add	r8,r0,r8

	lwz	r1,0(r8)

	add	r1,r0,r1

	li	r0,0

	stwu	r0,-16(r1)	/* establish a stack frame */

6:

arch/powerpc/boot/wrapper

+6 −3
Original line number Diff line number Diff line
@@ -39,6 +39,7 @@ dts= 
cacheit=

binary=

gzip=.gz

pie=



# cross-compilation prefix

CROSS=
@@ -157,9 +158,10 @@ pmac|chrp) 
    platformo=$object/of.o

    ;;

coff)

    platformo=$object/of.o

    platformo="$object/crt0.o $object/of.o"

    lds=$object/zImage.coff.lds

    link_address='0x500000'

    pie=

    ;;

miboot|uboot)

    # miboot and U-boot want just the bare bits, not an ELF binary
@@ -208,6 +210,7 @@ ps3) 
    ksection=.kernel:vmlinux.bin

    isection=.kernel:initrd

    link_address=''

    pie=

    ;;

ep88xc|ep405|ep8248e)

    platformo="$object/fixed-head.o $object/$platform.o"
@@ -310,9 +313,9 @@ fi 


if [ "$platform" != "miboot" ]; then

    if [ -n "$link_address" ] ; then

        text_start="-Ttext $link_address --defsym _start=$link_address"

        text_start="-Ttext $link_address"

    fi

    ${CROSS}ld -m elf32ppc -T $lds $text_start -o "$ofile" \

    ${CROSS}ld -m elf32ppc -T $lds $text_start $pie -o "$ofile" \

	$platformo $tmp $object/wrapper.a

    rm $tmp

fi

arch/powerpc/boot/zImage.coff.lds.S

+2 −4
Original line number Diff line number Diff line
@@ -3,13 +3,13 @@ ENTRY(_zimage_start_opd) 
EXTERN(_zimage_start_opd)

SECTIONS

{

  _start = .;

  .text      :

  {

    _start = .;

    *(.text)

    *(.fixup)

  }

    _etext = .;

  }

  . = ALIGN(4096);

  .data    :

  {
@@ -17,9 +17,7 @@ SECTIONS 
    *(.data*)

    *(__builtin_*)

    *(.sdata*)

    __got2_start = .;

    *(.got2)

    __got2_end = .;



    _dtb_start = .;

    *(.kernel:dtb)

arch/powerpc/boot/zImage.lds.S

+36 −21
Original line number Diff line number Diff line
@@ -3,49 +3,64 @@ ENTRY(_zimage_start) 
EXTERN(_zimage_start)

SECTIONS

{

  _start = .;

  .text      :

  {

    _start = .;

    *(.text)

    *(.fixup)

  }

    _etext = .;

  }

  . = ALIGN(4096);

  .data    :

  {

    *(.rodata*)

    *(.data*)

    *(.sdata*)

    __got2_start = .;

    *(.got2)

    __got2_end = .;

  }

  .dynsym : { *(.dynsym) }

  .dynstr : { *(.dynstr) }

  .dynamic :

  {

    __dynamic_start = .;

    *(.dynamic)

  }

  .hash : { *(.hash) }

  .interp : { *(.interp) }

  .rela.dyn : { *(.rela*) }



  . = ALIGN(8);

  .kernel:dtb :

  {

    _dtb_start = .;

  .kernel:dtb : { *(.kernel:dtb) }

    *(.kernel:dtb)

    _dtb_end = .;

  }



  . = ALIGN(4096);

  .kernel:vmlinux.strip :

  {

    _vmlinux_start =  .;

  .kernel:vmlinux.strip : { *(.kernel:vmlinux.strip) }

    *(.kernel:vmlinux.strip)

    _vmlinux_end =  .;

  }



  . = ALIGN(4096);

  .kernel:initrd :

  {

    _initrd_start =  .;

  .kernel:initrd : { *(.kernel:initrd) }

    *(.kernel:initrd)

    _initrd_end =  .;

  }



  . = ALIGN(4096);

  _edata  =  .;



  . = ALIGN(4096);

  __bss_start = .;

  .bss       :

  {

    _edata  =  .;

    __bss_start = .;

    *(.sbss)

    *(.bss)

  }

  . = ALIGN(4096);

    *(COMMON)

    _end = . ;

  }

}

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