Re: [PATCH] [ARM] 5428/1: Module relocation update for R_ARM_V4BX

From: Russell King
Date: Sun Mar 29 2009 - 04:52:37 EST

From: Daniel Silverstone <dsilvers@xxxxxxxxxxxx>

It would seem when building kernel modules with modern binutils
(required by modern GCC) for ARM v4T targets (specifically observed
with the Samsung 24xx SoC which is an 920T) R_ARM_V4BX relocations
are emitted for function epilogues.

This manifests at module load time with an "unknown relocation: 40"
error message.

The following patch adds the R_ARM_V4BX relocation to the ARM kernel
module loader. The relocation operation is taken from that within the
binutils bfd library.

Signed-off-by: Simtec Linux Team <linux@xxxxxxxxxxxx>
Signed-off-by: Vincent Sanders <vince@xxxxxxxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
arch/arm/include/asm/elf.h | 1 +
arch/arm/kernel/module.c | 9 +++++++++
2 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/arch/arm/include/asm/elf.h b/arch/arm/include/asm/elf.h
index a58378c..ce3b36e 100644
--- a/arch/arm/include/asm/elf.h
+++ b/arch/arm/include/asm/elf.h
@@ -50,6 +50,7 @@ typedef struct user_fp elf_fpregset_t;
#define R_ARM_ABS32 2
#define R_ARM_CALL 28
#define R_ARM_JUMP24 29
+#define R_ARM_V4BX 40

* These are used to set parameters in the core dumps.
diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
index dab48f2..9f509fd 100644
--- a/arch/arm/kernel/module.c
+++ b/arch/arm/kernel/module.c
@@ -132,6 +132,15 @@ apply_relocate(Elf32_Shdr *sechdrs, const char *strtab, unsigned int symindex,
*(u32 *)loc |= offset & 0x00ffffff;

+ case R_ARM_V4BX:
+ /* Preserve Rm and the condition code. Alter
+ * other bits to re-code instruction as
+ * MOV PC,Rm.
+ */
+ *(u32 *)loc &= 0xf000000f;
+ *(u32 *)loc |= 0x01a0f000;
+ break;
printk(KERN_ERR "%s: unknown relocation: %u\n",
module->name, ELF32_R_TYPE(rel->r_info));
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