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

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@simtec.co.uk>
Signed-off-by: Vincent Sanders <vince@simtec.co.uk>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

2 files changed, 10 insertions, 0 deletions

diff --git a/arch/arm/include/asm/elf.h b/arch/arm/include/asm/elf.h
index a58378c343b9..ce3b36e9df81 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 dab48f27263f..9f509fd00fda 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));