linux-kernel - Re: [PATCH] [ARM] 5428/1: Module relocation update for R_ARM

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Date:	Sat, 28 Mar 2009 20:30:26 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	stable@...nel.org,
	Linux Kernel Mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [ARM] 5428/1: Module relocation update for R_ARM_V4BX

From: Daniel Silverstone <dsilvers@...tec.co.uk>

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@...tec.co.uk>
Signed-off-by: Vincent Sanders <vince@...tec.co.uk>
Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
---
 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;
 			break;
 
+	       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;
+
 		default:
 			printk(KERN_ERR "%s: unknown relocation: %u\n",
 			       module->name, ELF32_R_TYPE(rel->r_info));
--
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