This changes the way we make the boot wrapper position-independent.
Before we just added the offset (the difference between runtime
address and link address) to each entry in the .got2 section. That
doesn't relocate pointer values in initialized variables and arrays.
Instead we now link the bootwrapper with -pie to get a position-
independent executable, and process the relocations in the dynamic
relocation section that the linker puts into the executable. This
means that initialized variables and arrays get relocated properly.
Currently we only process R_PPC_RELATIVE relocations, which is all we
get provided C files are compiled with -fPIC (which they are already)
and assembly code is written to be position-independent. Some of the
changes below are to make parts of crt0.S be PIC code (i.e. generate
no relocations other than R_PPC_RELATIVE).
The relocation code below does nothing if there is no dynamic section,
which means that we can link without -pie and it will work provided
that the bootwrapper executable is loaded at its linked-at address.
Signed-off-by: Paul Mackerras <[EMAIL PROTECTED]>
---
diff --git a/arch/powerpc/boot/crt0.S b/arch/powerpc/boot/crt0.S
index f1c4dfc..a6901c3 100644
--- a/arch/powerpc/boot/crt0.S
+++ b/arch/powerpc/boot/crt0.S
@@ -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 +36,60 @@ _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,[EMAIL PROTECTED]
- addi r9,r9,[EMAIL PROTECTED]
- 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,[EMAIL PROTECTED]
- addi r9,r9,[EMAIL PROTECTED]
- lis r8,[EMAIL PROTECTED]
- addi r8,r8,[EMAIL PROTECTED]
- 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,[EMAIL PROTECTED]
+ 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: or. r8,r0,r9 /* skip relocation if we don't have both */
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
+ 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,[EMAIL PROTECTED]
- addi r9,r9,[EMAIL PROTECTED]
- add r9,r0,r9
- lis r8,[EMAIL PROTECTED]
- addi r8,r8,[EMAIL PROTECTED]
- 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 +99,19 @@ _zimage_start_lib:
isync
/* Clear the BSS */
- lis r9,[EMAIL PROTECTED]
- addi r9,r9,[EMAIL PROTECTED]
- add r9,r0,r9
- lis r8,[EMAIL PROTECTED]
- addi r8,r8,[EMAIL PROTECTED]
- 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,[EMAIL PROTECTED]
- addi r8,r8,[EMAIL PROTECTED]
+ 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:
diff --git a/arch/powerpc/boot/wrapper b/arch/powerpc/boot/wrapper
index 644bf9d..64653b3 100755
--- a/arch/powerpc/boot/wrapper
+++ b/arch/powerpc/boot/wrapper
@@ -39,6 +39,7 @@ dts=
cacheit=
binary=
gzip=.gz
+pie=-pie
# cross-compilation prefix
CROSS=
@@ -149,9 +150,10 @@ 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
@@ -197,6 +199,7 @@ ps3)
ksection=.kernel:vmlinux.bin
isection=.kernel:initrd
link_address=''
+ pie=
;;
ep88xc|ep405|ep8248e)
platformo="$object/fixed-head.o $object/$platform.o"
@@ -288,9 +291,9 @@ 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
diff --git a/arch/powerpc/boot/zImage.coff.lds.S
b/arch/powerpc/boot/zImage.coff.lds.S
index 856dc78..de4c9e3 100644
--- a/arch/powerpc/boot/zImage.coff.lds.S
+++ b/arch/powerpc/boot/zImage.coff.lds.S
@@ -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)
diff --git a/arch/powerpc/boot/zImage.lds.S b/arch/powerpc/boot/zImage.lds.S
index 0962d62..05af879 100644
--- a/arch/powerpc/boot/zImage.lds.S
+++ b/arch/powerpc/boot/zImage.lds.S
@@ -3,49 +3,63 @@ 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 = .;
-
- . = ALIGN(4096);
- _vmlinux_start = .;
- .kernel:vmlinux.strip : { *(.kernel:vmlinux.strip) }
- _vmlinux_end = .;
+ .kernel:dtb :
+ {
+ _dtb_start = .;
+ *(.kernel:dtb)
+ _dtb_end = .;
+ }
. = ALIGN(4096);
- _initrd_start = .;
- .kernel:initrd : { *(.kernel:initrd) }
- _initrd_end = .;
+ .kernel:vmlinux.strip :
+ {
+ _vmlinux_start = .;
+ *(.kernel:vmlinux.strip)
+ _vmlinux_end = .;
+ }
. = ALIGN(4096);
- _edata = .;
+ .kernel:initrd :
+ {
+ _initrd_start = .;
+ *(.kernel:initrd)
+ _initrd_end = .;
+ }
. = ALIGN(4096);
- __bss_start = .;
.bss :
{
- *(.sbss)
- *(.bss)
+ _edata = .;
+ __bss_start = .;
+ *(.sbss)
+ *(.bss)
+ _end = . ;
}
- . = ALIGN(4096);
- _end = . ;
}
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