Re: [PATCH 04/19] ARM: implement elf_apply_relocations() for ELF relocation support

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hi,

On 1/5/26 12:26 PM, Sascha Hauer wrote:
> Implement architecture-specific ELF relocation handlers for ARM32 and ARM64.
> 
> ARM32 implementation (arch/arm/lib32/elf_reloc.c):
> - Handles REL-format relocations (no explicit addend)
> - Supports R_ARM_RELATIVE and R_ARM_ABS32 relocation types
> - Addend is read from the target location
> 
> ARM64 implementation (arch/arm/lib64/elf_reloc.c):
> - Handles RELA-format relocations (with explicit addend)
> - Supports R_AARCH64_RELATIVE and R_AARCH64_ABS64 relocation types
> - Addend is provided in relocation entry
> 
> Both implementations:
> - Parse PT_DYNAMIC segment to locate relocation tables
> - Validate relocation table format and entry sizes
> - Apply relocations based on the computed load offset
> - Return appropriate errors for unsupported relocation types
> 
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
> ---
>  arch/arm/include/asm/elf.h |  11 +++++
>  arch/arm/lib32/Makefile    |   1 +
>  arch/arm/lib32/elf_reloc.c | 105 +++++++++++++++++++++++++++++++++++++++++++++
>  arch/arm/lib64/Makefile    |   1 +
>  arch/arm/lib64/elf_reloc.c | 105 +++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 223 insertions(+)
> 
> diff --git a/arch/arm/include/asm/elf.h b/arch/arm/include/asm/elf.h
> index 4043e6fd5b991eb5cccb3fa0ea28d208006ee1fc..cceb92ee1a5f63c37b0e981c263676bd35a261c0 100644
> --- a/arch/arm/include/asm/elf.h
> +++ b/arch/arm/include/asm/elf.h
> @@ -36,6 +36,17 @@ typedef struct user_fp elf_fpregset_t;
>  #define R_ARM_THM_CALL		10
>  #define R_ARM_THM_JUMP24	30
>  
> +/* Additional relocation types for dynamic linking */
> +#define R_ARM_RELATIVE		23

This is already defined in arch/arm/cpu/common.c, you can guess where
this is going ;)

> +#define R_ARM_GLOB_DAT		21
> +#define R_ARM_JUMP_SLOT		22

These two are not used.

> +
> +#define R_AARCH64_NONE		0
> +#define R_AARCH64_ABS64		257
> +#define R_AARCH64_RELATIVE	1027
> +#define R_AARCH64_GLOB_DAT	1025
> +#define R_AARCH64_JUMP_SLOT	1026

Likewise, only R_AARCH64_JUMP_SLOT and R_AARCH64_GLOB_DAT are not used.

> +/*
> + * Parse dynamic section and extract relocation info for ARM32
> + */
> +static int parse_dynamic_section(struct elf_image *elf, Elf32_Dyn *dyn,
> +				  Elf32_Rel **rel_out, u64 *relsz_out)
> +{
> +	Elf32_Rel *rel = NULL;

If we define ELF_CLASS depending on CONFIG_ARM32/CONFIG_ARM64, we can
write a generic parse_dynamic_section() that applies to all architectures.

In this case, we would just collect both REL and RELA in the switch and
just use what's available.
> +int elf_apply_relocations(struct elf_image *elf, void *dyn_seg)
> +{

We already have relocate_to_current_adr(). If we change it to call
a new relocate_image():

	relocate_image(get_runtime_offset(),
			runtime_addr(__rel_dyn_start),
			runtime_addr(__rel_dyn_end),
			runtime_addr(__dynsym_start),
			runtime_addr(__dynsym_end));

Then we could use relocate_image() in generic code instead of
duplicating it per architecture.

> +/*
> + * Parse dynamic section and extract relocation info for ARM64
> + */
> +static int parse_dynamic_section(struct elf_image *elf, Elf64_Dyn *dyn,
> +				  Elf64_Rela **rela_out, u64 *relasz_out)

Same comment as for ARM32. I believe this can go into generic code.

> +		case R_AARCH64_ABS64:
> +			/* B(P) = S + A */
> +			*fixup_addr = base + rela->r_addend;
> +			break;

What did you do to get R_AARCH64_ABS64 relocations? We don't handle them
in relocate_to_current_adr() and they shouldn't have been generated.


Thanks,
Ahmad

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