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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: Paul Mackerras <paulus@samba.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
hifive-unleashed-5.1
Michael Ellerman 2011-04-12 20:38:55 +00:00 committed by Benjamin Herrenschmidt
parent ee7a2aa3d3
commit 6975a783d7
4 changed files with 118 additions and 70 deletions
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116
arch/powerpc/boot/crt0.S
View File

@ -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 .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 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 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:

9
arch/powerpc/boot/wrapper
View File

@ -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

6
arch/powerpc/boot/zImage.coff.lds.S
View File

@ -3,13 +3,13 @@ ENTRY(_zimage_start_opd)
EXTERN(_zimage_start_opd)
SECTIONS
{
_start = .;
.text :
{
_start = .;
*(.text)
*(.fixup)
_etext = .;
}
_etext = .;
. = ALIGN(4096);
.data :
{
@ -17,9 +17,7 @@ SECTIONS
*(.data*)
*(__builtin_*)
*(.sdata*)
__got2_start = .;
*(.got2)
__got2_end = .;
_dtb_start = .;
*(.kernel:dtb)

57
arch/powerpc/boot/zImage.lds.S
View File

@ -3,49 +3,64 @@ ENTRY(_zimage_start)
EXTERN(_zimage_start)
SECTIONS
{
_start = .;
.text :
{
_start = .;
*(.text)
*(.fixup)
_etext = .;
}
_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);
_dtb_start = .;
.kernel:dtb : { *(.kernel:dtb) }
_dtb_end = .;
.kernel:dtb :
{
_dtb_start = .;
*(.kernel:dtb)
_dtb_end = .;
}
. = ALIGN(4096);
_vmlinux_start = .;
.kernel:vmlinux.strip : { *(.kernel:vmlinux.strip) }
_vmlinux_end = .;
.kernel:vmlinux.strip :
{
_vmlinux_start = .;
*(.kernel:vmlinux.strip)
_vmlinux_end = .;
}
. = ALIGN(4096);
_initrd_start = .;
.kernel:initrd : { *(.kernel:initrd) }
_initrd_end = .;
.kernel:initrd :
{
_initrd_start = .;
*(.kernel:initrd)
_initrd_end = .;
}
. = ALIGN(4096);
_edata = .;
. = ALIGN(4096);
__bss_start = .;
.bss :
{
*(.sbss)
*(.bss)
_edata = .;
__bss_start = .;
*(.sbss)
*(.bss)
*(COMMON)
_end = . ;
}
. = ALIGN(4096);
_end = . ;
}