llext: make unresolved symbol errors fatal

With experience it becomes clear, that failing to resolve symbols
during the linking process is likely fatal for the module loading and
a simple warning isn't enough. Fail loading instead.

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

arch/xtensa/core/elf.c

@@ -32,10 +32,10 @@ LOG_MODULE_DECLARE(llext, CONFIG_LLEXT_LOG_LEVEL);
 #define R_XTENSA_ASM_EXPAND	11
 #define R_XTENSA_SLOT0_OP	20
 
-static void xtensa_elf_relocate(struct llext_loader *ldr, struct llext *ext,
-				const elf_rela_t *rel, uintptr_t addr,
-				uint8_t *loc, int type, uint32_t stb,
-				const struct llext_load_param *ldr_parm)
+static int xtensa_elf_relocate(struct llext_loader *ldr, struct llext *ext,
+			       const elf_rela_t *rel, uintptr_t addr,
+			       uint8_t *loc, int type, uint32_t stb,
+			       const struct llext_load_param *ldr_parm)
 {
 	elf_word *got_entry = (elf_word *)loc;
 
@@ -59,7 +59,7 @@ static void xtensa_elf_relocate(struct llext_loader *ldr, struct llext *ext,
 
 		if (sh_ndx == ext->sect_cnt) {
 			LOG_ERR("%#x not found in any of the sections", *got_entry);
-			return;
+			return -ENOENT;
 		}
 
 		*got_entry += (uintptr_t)llext_loaded_sect_ptr(ldr, ext, sh_ndx) -
@@ -87,7 +87,7 @@ static void xtensa_elf_relocate(struct llext_loader *ldr, struct llext *ext,
 		}
 		if (ret) {
 			LOG_ERR("Failed to read a symbol table entry, LLEXT linking might fail.");
-			return;
+			return ret;
 		}
 
 		/*
@@ -124,19 +124,21 @@ static void xtensa_elf_relocate(struct llext_loader *ldr, struct llext *ext,
 	default:
 		LOG_DBG("Unsupported relocation type %u", type);
 
-		return;
+		return 0;
 	}
 
 	LOG_DBG("Applied relocation to %#x type %u at %p",
 		*(uint32_t *)((uintptr_t)got_entry & ~3), type, (void *)got_entry);
+
+	return 0;
 }
 
 /**
  * @brief Architecture specific function for STB_LOCAL ELF relocations
  */
-void arch_elf_relocate_local(struct llext_loader *ldr, struct llext *ext, const elf_rela_t *rel,
-			     const elf_sym_t *sym, uint8_t *rel_addr,
-			     const struct llext_load_param *ldr_parm)
+int arch_elf_relocate_local(struct llext_loader *ldr, struct llext *ext, const elf_rela_t *rel,
+			    const elf_sym_t *sym, uint8_t *rel_addr,
+			    const struct llext_load_param *ldr_parm)
 {
 	int type = ELF32_R_TYPE(rel->r_info);
 	uintptr_t sh_addr;
@@ -152,15 +154,15 @@ void arch_elf_relocate_local(struct llext_loader *ldr, struct llext *ext, const
 		sh_addr = ldr->sects[LLEXT_MEM_TEXT].sh_addr;
 	}
 
-	xtensa_elf_relocate(ldr, ext, rel, sh_addr, rel_addr, type, ELF_ST_BIND(sym->st_info),
-			    ldr_parm);
+	return xtensa_elf_relocate(ldr, ext, rel, sh_addr, rel_addr, type,
+				   ELF_ST_BIND(sym->st_info), ldr_parm);
 }
 
 /**
  * @brief Architecture specific function for STB_GLOBAL ELF relocations
  */
-void arch_elf_relocate_global(struct llext_loader *ldr, struct llext *ext, const elf_rela_t *rel,
-			      const elf_sym_t *sym, uint8_t *rel_addr, const void *link_addr)
+int arch_elf_relocate_global(struct llext_loader *ldr, struct llext *ext, const elf_rela_t *rel,
+			     const elf_sym_t *sym, uint8_t *rel_addr, const void *link_addr)
 {
 	int type = ELF32_R_TYPE(rel->r_info);
 
@@ -169,6 +171,6 @@ void arch_elf_relocate_global(struct llext_loader *ldr, struct llext *ext, const
 		LOG_WRN("global: non-zero relative value %#x", *(elf_word *)rel_addr);
 	}
 
-	xtensa_elf_relocate(ldr, ext, rel, (uintptr_t)link_addr, rel_addr, type,
-			    ELF_ST_BIND(sym->st_info), NULL);
+	return xtensa_elf_relocate(ldr, ext, rel, (uintptr_t)link_addr, rel_addr, type,
+				   ELF_ST_BIND(sym->st_info), NULL);
 }

include/zephyr/llext/llext.h

@@ -409,10 +409,11 @@ int llext_get_section_header(struct llext_loader *loader, struct llext *ext,
  * @param[in] sym Corresponding symbol table entry
  * @param[in] rel_addr Address where relocation should be performed
  * @param[in] ldr_parm Loader parameters
+ * @returns 0 on success or a negative error code
  */
-void arch_elf_relocate_local(struct llext_loader *loader, struct llext *ext, const elf_rela_t *rel,
-			     const elf_sym_t *sym, uint8_t *rel_addr,
-			     const struct llext_load_param *ldr_parm);
+int arch_elf_relocate_local(struct llext_loader *loader, struct llext *ext, const elf_rela_t *rel,
+			    const elf_sym_t *sym, uint8_t *rel_addr,
+			    const struct llext_load_param *ldr_parm);
 
 /**
  * @brief Architecture specific function for global binding relocations
@@ -423,9 +424,10 @@ void arch_elf_relocate_local(struct llext_loader *loader, struct llext *ext, con
  * @param[in] sym Corresponding symbol table entry
  * @param[in] rel_addr Address where relocation should be performed
  * @param[in] link_addr target address for table-based relocations
+ * @returns 0 on success or a negative error code
  */
-void arch_elf_relocate_global(struct llext_loader *loader, struct llext *ext, const elf_rela_t *rel,
-			      const elf_sym_t *sym, uint8_t *rel_addr, const void *link_addr);
+int arch_elf_relocate_global(struct llext_loader *loader, struct llext *ext, const elf_rela_t *rel,
+			     const elf_sym_t *sym, uint8_t *rel_addr, const void *link_addr);
 
 /**
  * @brief Initialize LLEXT heap dynamically

subsys/llext/llext_link.c

@@ -32,16 +32,18 @@ __weak int arch_elf_relocate(struct llext_loader *ldr, struct llext *ext, elf_re
 	return -ENOTSUP;
 }
 
-__weak void arch_elf_relocate_local(struct llext_loader *ldr, struct llext *ext,
+__weak int arch_elf_relocate_local(struct llext_loader *ldr, struct llext *ext,
 				    const elf_rela_t *rel, const elf_sym_t *sym, uint8_t *rel_addr,
 				    const struct llext_load_param *ldr_parm)
 {
+	return -ENOTSUP;
 }
 
-__weak void arch_elf_relocate_global(struct llext_loader *ldr, struct llext *ext,
-				     const elf_rela_t *rel, const elf_sym_t *sym, uint8_t *rel_addr,
-				     const void *link_addr)
+__weak int arch_elf_relocate_global(struct llext_loader *ldr, struct llext *ext,
+				    const elf_rela_t *rel, const elf_sym_t *sym, uint8_t *rel_addr,
+				    const void *link_addr)
 {
+	return -ENOTSUP;
 }
 
 /*
@@ -246,8 +248,8 @@ int llext_lookup_symbol(struct llext_loader *ldr, struct llext *ext, uintptr_t *
 	return 0;
 }
 
-static void llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr_t *shdr,
-			   const struct llext_load_param *ldr_parm, elf_shdr_t *tgt)
+static int llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr_t *shdr,
+			  const struct llext_load_param *ldr_parm, elf_shdr_t *tgt)
 {
 	unsigned int sh_cnt = shdr->sh_size / shdr->sh_entsize;
 	/*
@@ -255,6 +257,7 @@ static void llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr
 	 * reference point
 	 */
 	uint8_t *text = ext->mem[LLEXT_MEM_TEXT];
+	int link_err = 0;
 
 	LOG_DBG("Found %p in PLT %u size %zu cnt %u text %p",
 		(void *)llext_section_name(ldr, ext, shdr),
@@ -370,20 +373,34 @@ static void llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr
 
 			if (!link_addr) {
 				LOG_WRN("PLT: cannot find idx %u name %s", j, name);
-				continue;
+				/* Will fail after reporting all missing symbols */
+				if (!link_err) {
+					link_err = -ENOENT;
+				}
+				break;
 			}
 
 			/* Resolve the symbol */
-			arch_elf_relocate_global(ldr, ext, &rela, &sym, rel_addr, link_addr);
+			ret = arch_elf_relocate_global(ldr, ext, &rela, &sym, rel_addr, link_addr);
+			if (!link_err) {
+				link_err = ret;
+			}
 			break;
 		case STB_LOCAL:
-			arch_elf_relocate_local(ldr, ext, &rela, &sym, rel_addr, ldr_parm);
+			ret = arch_elf_relocate_local(ldr, ext, &rela, &sym, rel_addr, ldr_parm);
+			if (!link_err) {
+				link_err = ret;
+			}
 		}
 
-		LOG_DBG("symbol %s relocation @%p r-offset %#zx .text offset %#zx stb %u",
-			name, (void *)rel_addr,
-			(size_t)rela.r_offset, (size_t)ldr->sects[LLEXT_MEM_TEXT].sh_offset, stb);
+		if (!link_err) {
+			LOG_DBG("symbol %s relocation @%p r-offset %#zx .text offset %#zx stb %u",
+				name, (void *)rel_addr, (size_t)rela.r_offset,
+				(size_t)ldr->sects[LLEXT_MEM_TEXT].sh_offset, stb);
+		}
 	}
+
+	return link_err;
 }
 
 int llext_link(struct llext_loader *ldr, struct llext *ext, const struct llext_load_param *ldr_parm)
@@ -457,7 +474,10 @@ int llext_link(struct llext_loader *ldr, struct llext *ext, const struct llext_l
 				tgt = ext->sect_hdrs + shdr->sh_info;
 			}
 
-			llext_link_plt(ldr, ext, shdr, ldr_parm, tgt);
+			ret = llext_link_plt(ldr, ext, shdr, ldr_parm, tgt);
+			if (ret < 0) {
+				return ret;
+			}
 			continue;
 		}