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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>
This commit is contained in:
Michael Ellerman
Benjamin Herrenschmidt
parent
ee7a2aa3d3
commit
6975a783d7
@ -6,16 +6,28 @@
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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* NOTE: this code runs in 32 bit mode and is packaged as ELF32.
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* NOTE: this code runs in 32 bit mode, is position-independent,
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* and is packaged as ELF32.
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*/
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#include "ppc_asm.h"
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.text
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/* a procedure descriptor used when booting this as a COFF file */
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/* A procedure descriptor used when booting this as a COFF file.
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* When making COFF, this comes first in the link and we're
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* linked at 0x500000.
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*/
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.globl _zimage_start_opd
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_zimage_start_opd:
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.long _zimage_start, 0, 0, 0
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.long 0x500000, 0, 0, 0
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p_start: .long _start
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p_etext: .long _etext
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p_bss_start: .long __bss_start
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p_end: .long _end
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.weak _platform_stack_top
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p_pstack: .long _platform_stack_top
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.weak _zimage_start
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.globl _zimage_start
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@ -24,37 +36,65 @@ _zimage_start:
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_zimage_start_lib:
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/* Work out the offset between the address we were linked at
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and the address where we're running. */
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bl 1f
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1: mflr r0
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lis r9,1b@ha
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addi r9,r9,1b@l
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subf. r0,r9,r0
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beq 3f /* if running at same address as linked */
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bl .+4
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p_base: mflr r10 /* r10 now points to runtime addr of p_base */
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/* grab the link address of the dynamic section in r11 */
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addis r11,r10,(_GLOBAL_OFFSET_TABLE_-p_base)@ha
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lwz r11,(_GLOBAL_OFFSET_TABLE_-p_base)@l(r11)
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cmpwi r11,0
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beq 3f /* if not linked -pie */
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/* get the runtime address of the dynamic section in r12 */
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.weak __dynamic_start
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addis r12,r10,(__dynamic_start-p_base)@ha
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addi r12,r12,(__dynamic_start-p_base)@l
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subf r11,r11,r12 /* runtime - linktime offset */
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/* The .got2 section contains a list of addresses, so add
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the address offset onto each entry. */
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lis r9,__got2_start@ha
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addi r9,r9,__got2_start@l
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lis r8,__got2_end@ha
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addi r8,r8,__got2_end@l
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subf. r8,r9,r8
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/* The dynamic section contains a series of tagged entries.
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* We need the RELA and RELACOUNT entries. */
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RELA = 7
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RELACOUNT = 0x6ffffff9
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li r9,0
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li r0,0
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9: lwz r8,0(r12) /* get tag */
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cmpwi r8,0
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beq 10f /* end of list */
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cmpwi r8,RELA
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bne 11f
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lwz r9,4(r12) /* get RELA pointer in r9 */
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b 12f
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11: addis r8,r8,(-RELACOUNT)@ha
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cmpwi r8,RELACOUNT@l
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bne 12f
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lwz r0,4(r12) /* get RELACOUNT value in r0 */
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12: addi r12,r12,8
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b 9b
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/* The relocation section contains a list of relocations.
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* We now do the R_PPC_RELATIVE ones, which point to words
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* which need to be initialized with addend + offset.
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* The R_PPC_RELATIVE ones come first and there are RELACOUNT
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* of them. */
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10: /* skip relocation if we don't have both */
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cmpwi r0,0
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beq 3f
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srwi. r8,r8,2
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mtctr r8
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add r9,r0,r9
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2: lwz r8,0(r9)
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add r8,r8,r0
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stw r8,0(r9)
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addi r9,r9,4
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cmpwi r9,0
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beq 3f
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add r9,r9,r11 /* Relocate RELA pointer */
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mtctr r0
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2: lbz r0,4+3(r9) /* ELF32_R_INFO(reloc->r_info) */
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cmpwi r0,22 /* R_PPC_RELATIVE */
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bne 3f
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lwz r12,0(r9) /* reloc->r_offset */
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lwz r0,8(r9) /* reloc->r_addend */
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add r0,r0,r11
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stwx r0,r11,r12
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addi r9,r9,12
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bdnz 2b
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/* Do a cache flush for our text, in case the loader didn't */
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3: lis r9,_start@ha
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addi r9,r9,_start@l
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add r9,r0,r9
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lis r8,_etext@ha
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addi r8,r8,_etext@l
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add r8,r0,r8
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3: lwz r9,p_start-p_base(r10) /* note: these are relocated now */
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lwz r8,p_etext-p_base(r10)
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4: dcbf r0,r9
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icbi r0,r9
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addi r9,r9,0x20
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@ -64,27 +104,19 @@ _zimage_start_lib:
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isync
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/* Clear the BSS */
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lis r9,__bss_start@ha
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addi r9,r9,__bss_start@l
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add r9,r0,r9
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lis r8,_end@ha
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addi r8,r8,_end@l
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add r8,r0,r8
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li r10,0
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5: stw r10,0(r9)
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lwz r9,p_bss_start-p_base(r10)
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lwz r8,p_end-p_base(r10)
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li r0,0
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5: stw r0,0(r9)
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addi r9,r9,4
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cmplw cr0,r9,r8
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blt 5b
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/* Possibly set up a custom stack */
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.weak _platform_stack_top
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lis r8,_platform_stack_top@ha
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addi r8,r8,_platform_stack_top@l
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lwz r8,p_pstack-p_base(r10)
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cmpwi r8,0
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beq 6f
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add r8,r0,r8
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lwz r1,0(r8)
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add r1,r0,r1
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li r0,0
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stwu r0,-16(r1) /* establish a stack frame */
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6:
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@ -39,6 +39,7 @@ dts=
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cacheit=
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binary=
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gzip=.gz
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pie=
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# cross-compilation prefix
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CROSS=
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@ -157,9 +158,10 @@ pmac|chrp)
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platformo=$object/of.o
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;;
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coff)
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platformo=$object/of.o
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platformo="$object/crt0.o $object/of.o"
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lds=$object/zImage.coff.lds
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link_address='0x500000'
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pie=
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;;
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miboot|uboot)
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# miboot and U-boot want just the bare bits, not an ELF binary
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@ -208,6 +210,7 @@ ps3)
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ksection=.kernel:vmlinux.bin
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isection=.kernel:initrd
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link_address=''
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pie=
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;;
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ep88xc|ep405|ep8248e)
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platformo="$object/fixed-head.o $object/$platform.o"
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@ -310,9 +313,9 @@ fi
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if [ "$platform" != "miboot" ]; then
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if [ -n "$link_address" ] ; then
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text_start="-Ttext $link_address --defsym _start=$link_address"
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text_start="-Ttext $link_address"
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fi
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${CROSS}ld -m elf32ppc -T $lds $text_start -o "$ofile" \
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${CROSS}ld -m elf32ppc -T $lds $text_start $pie -o "$ofile" \
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$platformo $tmp $object/wrapper.a
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rm $tmp
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fi
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@ -3,13 +3,13 @@ ENTRY(_zimage_start_opd)
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EXTERN(_zimage_start_opd)
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SECTIONS
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{
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_start = .;
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.text :
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{
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_start = .;
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*(.text)
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*(.fixup)
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_etext = .;
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}
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_etext = .;
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. = ALIGN(4096);
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.data :
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{
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@ -17,9 +17,7 @@ SECTIONS
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*(.data*)
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*(__builtin_*)
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*(.sdata*)
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__got2_start = .;
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*(.got2)
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__got2_end = .;
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_dtb_start = .;
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*(.kernel:dtb)
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@ -3,49 +3,64 @@ ENTRY(_zimage_start)
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EXTERN(_zimage_start)
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SECTIONS
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{
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_start = .;
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.text :
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{
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_start = .;
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*(.text)
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*(.fixup)
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_etext = .;
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}
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_etext = .;
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. = ALIGN(4096);
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.data :
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{
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*(.rodata*)
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*(.data*)
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*(.sdata*)
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__got2_start = .;
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*(.got2)
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__got2_end = .;
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}
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.dynsym : { *(.dynsym) }
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.dynstr : { *(.dynstr) }
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.dynamic :
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{
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__dynamic_start = .;
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*(.dynamic)
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}
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.hash : { *(.hash) }
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.interp : { *(.interp) }
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.rela.dyn : { *(.rela*) }
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. = ALIGN(8);
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_dtb_start = .;
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.kernel:dtb : { *(.kernel:dtb) }
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_dtb_end = .;
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.kernel:dtb :
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{
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_dtb_start = .;
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*(.kernel:dtb)
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_dtb_end = .;
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}
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. = ALIGN(4096);
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_vmlinux_start = .;
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.kernel:vmlinux.strip : { *(.kernel:vmlinux.strip) }
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_vmlinux_end = .;
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.kernel:vmlinux.strip :
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{
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_vmlinux_start = .;
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*(.kernel:vmlinux.strip)
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_vmlinux_end = .;
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}
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. = ALIGN(4096);
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_initrd_start = .;
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.kernel:initrd : { *(.kernel:initrd) }
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_initrd_end = .;
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.kernel:initrd :
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{
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_initrd_start = .;
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*(.kernel:initrd)
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_initrd_end = .;
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}
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. = ALIGN(4096);
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_edata = .;
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. = ALIGN(4096);
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__bss_start = .;
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.bss :
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{
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*(.sbss)
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*(.bss)
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_edata = .;
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__bss_start = .;
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*(.sbss)
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*(.bss)
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*(COMMON)
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_end = . ;
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}
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. = ALIGN(4096);
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_end = . ;
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}
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