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Message-Id: <1484681173-11644-3-git-send-email-ard.biesheuvel@linaro.org>
Date: Tue, 17 Jan 2017 19:26:12 +0000
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: linux-kernel@...r.kernel.org, mpe@...erman.id.au, jeyu@...hat.com
Cc: rusty@...tcorp.com.au, suzuki.poulose@....com, will.deacon@....com,
akpm@...ux-foundation.org, benh@...nel.crashing.org,
paulus@...ba.org, arnd@...db.de, torvalds@...ux-foundation.org,
viro@...iv.linux.org.uk, linuxppc-dev@...ts.ozlabs.org,
Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: [PATCH v4 2/3] powerpc/reloc64: add support for 32-bit CRC pseudo-symbols
In preparation of modifying the core modversions code to emit the CRCs
as 32-bit quantities, ensure that 64-bit PowerPC will be able to deal
with this when CONFIG_RELOCATABLE=y, in which case the CRCs will be
emitted into the final ELF binary as R_PPC64_ADDR32 relocations.
Since 32-bit relocations cannot be used to relocate memory addresses on
64-bit architectures, and since the CRC pseudo-symbol references are
emitted as anonymous relocations (i.e., against the NULL symbol in the
.dynsym section) with the final value recorded in the addend (*), we
can disregard any relocations where the symbol index != 0.
* Note that unsatisfied CRC pseudo-symbol references are emitted as
R_PPC64_ADDR32 relocations against named symbols that are typed as
weak undefined in the .dynsym symbol table. These can simply be
ignored (as before), considering that zero CRCs are interpreted as
missing, and the module code deals with that accordingly.
As it turns out, binutils for powerpc does not account for any relocations
beyond R_PPC64_RELATIVE ones in the RELACOUNT field of the .dynamic section,
which is unfortunate, since we need to do extra work to figure out the size
of the relocation array. So with a little help from the linker scripts,
grab an end pointer rather than a count, and iterate over the entire section.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
---
arch/powerpc/kernel/reloc_64.S | 60 ++++++++++++--------
arch/powerpc/kernel/vmlinux.lds.S | 1 +
arch/powerpc/relocs_check.sh | 5 +-
3 files changed, 40 insertions(+), 26 deletions(-)
diff --git a/arch/powerpc/kernel/reloc_64.S b/arch/powerpc/kernel/reloc_64.S
index d88736fbece6..e50f5d778ea2 100644
--- a/arch/powerpc/kernel/reloc_64.S
+++ b/arch/powerpc/kernel/reloc_64.S
@@ -12,8 +12,8 @@
#include <asm/ppc_asm.h>
RELA = 7
-RELACOUNT = 0x6ffffff9
R_PPC64_RELATIVE = 22
+R_PPC64_ADDR32 = 1
/*
* r3 = desired final address of kernel
@@ -29,29 +29,27 @@ _GLOBAL(relocate)
add r9,r9,r12 /* r9 has runtime addr of .rela.dyn section */
ld r10,(p_st - 0b)(r12)
add r10,r10,r12 /* r10 has runtime addr of _stext */
+ ld r8,(p_rela_end - 0b)(r12)
+ add r8,r8,r12 /* r8 has addr of end of .rela.dyn section */
/*
- * Scan the dynamic section for the RELA and RELACOUNT entries.
+ * Scan the dynamic section for the RELA entry.
+ * NOTE: the RELACOUNT entry only covers R_PPC64_RELATIVE relocations,
+ * so we cannot use it here.
*/
li r7,0
- li r8,0
1: ld r6,0(r11) /* get tag */
cmpdi r6,0
- beq 4f /* end of list */
+ beq 3f /* end of list */
cmpdi r6,RELA
- bne 2f
- ld r7,8(r11) /* get RELA pointer in r7 */
- b 3f
-2: addis r6,r6,(-RELACOUNT)@ha
- cmpdi r6,RELACOUNT@l
- bne 3f
- ld r8,8(r11) /* get RELACOUNT value in r8 */
-3: addi r11,r11,16
+ beq 2f
+ addi r11,r11,16
b 1b
-4: cmpdi r7,0 /* check we have both RELA and RELACOUNT */
- cmpdi cr1,r8,0
- beq 6f
- beq cr1,6f
+2: ld r7,8(r11) /* get RELA pointer in r7 */
+3: cmpdi r7,0 /* check we have both RELA and a non-empty */
+ cmpd cr1,r8,r9 /* .rela.dyn section */
+ beq 7f
+ beq cr1,7f
/*
* Work out linktime address of _stext and hence the
@@ -63,26 +61,40 @@ _GLOBAL(relocate)
subf r7,r7,r9 /* cur_offset */
subf r10,r7,r10
subf r3,r10,r3 /* final_offset */
+ b 4f
/*
* Run through the list of relocations and process the
- * R_PPC64_RELATIVE ones.
+ * R_PPC64_RELATIVE and R_PPC64_ADDR32 ones.
*/
- mtctr r8
-5: ld r0,8(9) /* ELF64_R_TYPE(reloc->r_info) */
+3: addi r9,r9,24
+4: cmpd r9,r8
+ beq 7f
+5: ld r0,8(9) /* reloc->r_info (type *and* symbol index) */
+ ld r6,0(r9) /* reloc->r_offset */
cmpdi r0,R_PPC64_RELATIVE
bne 6f
- ld r6,0(r9) /* reloc->r_offset */
ld r0,16(r9) /* reloc->r_addend */
add r0,r0,r3
stdx r0,r7,r6
- addi r9,r9,24
- bdnz 5b
+ b 3b
+
+ /*
+ * CRCs of exported symbols are emitted as 32-bit relocations against
+ * the NULL .dynsym entry, with the CRC value recorded in the addend.
+ */
+6: cmpdi r0,R_PPC64_ADDR32
+ bne 3b
+ ld r0,16(r9) /* reloc->r_addend */
+ stwx r0,r7,r6
+ b 3b
+
+7: blr
-6: blr
.balign 8
p_dyn: .llong __dynamic_start - 0b
p_rela: .llong __rela_dyn_start - 0b
+p_rela_end:
+ .llong __rela_dyn_end - 0b
p_st: .llong _stext - 0b
-
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 7394b770ae1f..654728fc860d 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -241,6 +241,7 @@ SECTIONS
{
__rela_dyn_start = .;
*(.rela*)
+ __rela_dyn_end = .;
}
#endif
/* .exit.data is discarded at runtime, not link time,
diff --git a/arch/powerpc/relocs_check.sh b/arch/powerpc/relocs_check.sh
index ec2d5c835170..f9636b4e4548 100755
--- a/arch/powerpc/relocs_check.sh
+++ b/arch/powerpc/relocs_check.sh
@@ -30,7 +30,7 @@ bad_relocs=$(
# On PPC64:
# R_PPC64_RELATIVE, R_PPC64_NONE
# R_PPC64_ADDR64 mach_<name>
- # R_PPC64_ADDR64 __crc_<name>
+ # R_PPC64_ADDR32 __crc_<name>
# On PPC:
# R_PPC_RELATIVE, R_PPC_ADDR16_HI,
# R_PPC_ADDR16_HA,R_PPC_ADDR16_LO,
@@ -43,7 +43,8 @@ R_PPC_ADDR16_HA
R_PPC_RELATIVE
R_PPC_NONE' |
grep -E -v '\<R_PPC64_ADDR64[[:space:]]+mach_' |
- grep -E -v '\<R_PPC64_ADDR64[[:space:]]+__crc_'
+ grep -E -v '\<R_PPC64_ADDR32[[:space:]]+__crc_' |
+ grep -E -v '\<R_PPC64_ADDR32[[:space:]]+\*ABS\*'
)
if [ -z "$bad_relocs" ]; then
--
2.7.4
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