llext: xtensa: add support for local symbol relocations

Add support for relocating local symbols, as specified in the
.rela.dyn section.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>

arch/xtensa/core/CMakeLists.txt

@@ -24,6 +24,7 @@ zephyr_library_sources_ifdef(CONFIG_GDBSTUB gdbstub.c)
 zephyr_library_sources_ifdef(CONFIG_XTENSA_MMU ptables.c mmu.c)
 zephyr_library_sources_ifdef(CONFIG_USERSPACE userspace.S)
 zephyr_library_sources_ifdef(CONFIG_XTENSA_SYSCALL_USE_HELPER syscall_helper.c)
+zephyr_library_sources_ifdef(CONFIG_LLEXT elf.c)
 
 zephyr_library_sources_ifdef(
   CONFIG_KERNEL_VM_USE_CUSTOM_MEM_RANGE_CHECK

arch/xtensa/core/elf.c

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2023 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/llext/elf.h>
+#include <zephyr/llext/llext.h>
+#include <zephyr/logging/log.h>
+
+LOG_MODULE_DECLARE(llext);
+
+#define R_XTENSA_NONE           0
+#define R_XTENSA_32             1
+#define R_XTENSA_RTLD           2
+#define R_XTENSA_GLOB_DAT       3
+#define R_XTENSA_JMP_SLOT       4
+#define R_XTENSA_RELATIVE       5
+#define R_XTENSA_PLT            6
+
+/**
+ * @brief Architecture specific function for relocating shared elf
+ *
+ * Elf files contain a series of relocations described in multiple sections.
+ * These relocation instructions are architecture specific and each architecture
+ * supporting modules must implement this.
+ */
+void arch_elf_relocate_local(struct llext_loader *ldr, struct llext *ext,
+			     elf_rela_t *rel, size_t got_offset)
+{
+	uint8_t *text = ext->mem[LLEXT_MEM_TEXT];
+	int type = ELF32_R_TYPE(rel->r_info);
+
+	if (type == R_XTENSA_RELATIVE) {
+		elf_word ptr_offset = *(elf_word *)(text + got_offset);
+
+		LOG_DBG("relocation type %u offset %#x value %#x",
+			type, got_offset, ptr_offset);
+
+		/* Relocate a local symbol: Xtensa specific */
+		*(elf_word *)(text + got_offset) = (elf_word)(text + ptr_offset -
+							      ldr->sects[LLEXT_SECT_TEXT].sh_addr);
+	}
+}

include/zephyr/llext/llext.h

@@ -142,6 +142,17 @@ int llext_call_fn(struct llext *ext, const char *sym_name);
  */
 void arch_elf_relocate(elf_rela_t *rel, uintptr_t opaddr, uintptr_t opval);
 
+/**
+ * @brief Architecture specific function for updating addresses via relocation table
+ *
+ * @param[in] loader Extension loader data and context
+ * @param[in] ext Extension to call function in
+ * @param[in] rel Relocation data provided by elf
+ * @param[in] got_offset Offset within a relocation table
+ */
+void arch_elf_relocate_local(struct llext_loader *loader, struct llext *ext,
+			     elf_rela_t *rel, size_t got_offset);
+
 /**
  * @}
  */

subsys/llext/llext.c

@@ -462,6 +462,11 @@ static size_t llext_file_offset(struct llext_loader *ldr, size_t offset)
 	return offset;
 }
 
+__weak void arch_elf_relocate_local(struct llext_loader *ldr, struct llext *ext,
+				    elf_rela_t *rel, size_t got_offset)
+{
+}
+
 static void llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr_t *shdr)
 {
 	unsigned int sh_cnt = shdr->sh_size / shdr->sh_entsize;
@@ -514,6 +519,7 @@ static void llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr
 		}
 
 		uint32_t stt = ELF_ST_TYPE(sym_tbl.st_info);
+		uint32_t stb = ELF_ST_BIND(sym_tbl.st_info);
 		const char *name = llext_string(ldr, ext, LLEXT_MEM_STRTAB, sym_tbl.st_name);
 		/*
 		 * Both r_offset and sh_addr are addresses for which the extension
@@ -522,8 +528,14 @@ static void llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr
 		size_t got_offset = llext_file_offset(ldr, rela.r_offset) -
 			ldr->sects[LLEXT_SECT_TEXT].sh_offset;
 
-		if (stt == STT_NOTYPE && sym_tbl.st_shndx == SHN_UNDEF && name[0] != '\0') {
+		if (stt != STT_NOTYPE || sym_tbl.st_shndx != SHN_UNDEF)
-			const void *link_addr = llext_find_sym(NULL, name);
+			continue;
+
+		const void *link_addr;
+
+		switch (stb) {
+		case STB_GLOBAL:
+			link_addr = llext_find_sym(NULL, name);
 
 			if (!link_addr) {
 				LOG_WRN("PLT: cannot find idx %u name %s", j, name);
@@ -541,6 +553,9 @@ static void llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr
 
 			/* Resolve the symbol */
 			*(const void **)(text + got_offset) = link_addr;
+			break;
+		case  STB_LOCAL:
+			arch_elf_relocate_local(ldr, ext, &rela, got_offset);
 		}
 	}
 }