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llext: arm: Add R_ARM_ARM_THM_CALL reloc support

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Add support for the relocation type R_ARM_ARM_THM_CALL which is
produced for the ARM Thumb BL and BLX (branch immediate)
instructions.

These instructions are used for non-static functions like

void test1(void)
{
}

void main(void)
{
        test1();
}

Without support for this relocation, test1() has to be static.

Signed-off-by: Bjarki Arge Andreasen <bjarki@arge-andreasen.me>
This commit is contained in:
Bjarki Arge Andreasen 2024-03-12 14:13:53 +01:00 committed by Fabio Baltieri
parent 5cac834bb6
commit 9b583cc539
2 changed files with 50 additions and 0 deletions
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49
arch/arm/core/elf.c
View file

@ -7,9 +7,48 @@
#include <zephyr/llext/elf.h>
#include <zephyr/llext/llext.h>
#include <zephyr/logging/log.h>
#include <zephyr/sys/util.h>
LOG_MODULE_REGISTER(elf, CONFIG_LLEXT_LOG_LEVEL);
#define ARM_BL_BLX_UPPER_S_BIT BIT(10)
#define ARM_BL_BLX_ADDEND_OFFSET 0
#define ARM_BL_BLX_ADDEND_SIZE 11
#define ARM_BL_BLX_ADDEND_MASK 0x7FF
#define ARM_BL_BLX_HDR_MASK 0xF800
#define ARM_BL_BLX_LOWER_T1T2_BIT BIT(12)
static int32_t arm_bl_blx_decode_addend(uintptr_t opaddr)
{
uint16_t upper = *((uint16_t *)opaddr);
uint16_t lower = *(((uint16_t *)opaddr) + 1);
int32_t addend = upper & ARM_BL_BLX_UPPER_S_BIT ? UINT32_MAX : 0;
addend <<= ARM_BL_BLX_ADDEND_SIZE;
addend |= upper & ARM_BL_BLX_ADDEND_MASK;
addend <<= ARM_BL_BLX_ADDEND_SIZE;
addend |= lower & ARM_BL_BLX_ADDEND_MASK;
return lower & ARM_BL_BLX_LOWER_T1T2_BIT ? addend << 1 : addend << 2;
}
static void arm_bl_blx_encode_addend(uintptr_t opaddr, int32_t addend)
{
uint16_t upper = *((uint16_t *)opaddr);
uint16_t lower = *(((uint16_t *)opaddr) + 1);
addend = upper & ARM_BL_BLX_UPPER_S_BIT ? addend >> 1 : addend >> 2;
upper &= ARM_BL_BLX_HDR_MASK;
lower &= ARM_BL_BLX_HDR_MASK;
upper |= (addend >> ARM_BL_BLX_ADDEND_SIZE) & ARM_BL_BLX_ADDEND_MASK;
lower |= addend & ARM_BL_BLX_ADDEND_MASK;
*((uint16_t *)opaddr) = upper;
*(((uint16_t *)opaddr) + 1) = lower;
}
/**
* @brief Architecture specific function for relocating partially linked (static) elf
*
@ -32,6 +71,16 @@ void arch_elf_relocate(elf_rela_t *rel, uintptr_t opaddr, uintptr_t opval)
/* Update the absolute address of a load/store instruction */
*((uint32_t *)opaddr) = (uint32_t)opval;
break;
case R_ARM_THM_CALL:
/* Decode the initial addend */
int32_t addend = arm_bl_blx_decode_addend(opaddr);
/* Calculate and add the branch offset (addend) */
addend += ((int32_t)opval) - ((int32_t)opaddr);
/* Encode the addend */
arm_bl_blx_encode_addend(opaddr, addend);
break;
default:
LOG_DBG("Unsupported ARM elf relocation type %d at address %lx",
reloc_type, opaddr);

1
include/zephyr/llext/elf.h
View file

@ -371,6 +371,7 @@ struct elf64_rela {
#define R_ARM_ABS32 2
#define R_ARM_REL32 3
#define R_ARM_COPY 4
#define R_ARM_THM_CALL 10
#define R_ARM_CALL 28
#define R_ARM_V4BX 40