Commit 2255b638 authored by Eric Ackermann's avatar Eric Ackermann Committed by Carles Cufi
Browse files

llext: Refactor symbol lookup logic into function 



This commit refactors logic in llext_link.c that resolves
a symbol to be imported by an llext into a utility function.
Thereby, the logic can be re-used in other functions if
needed, e.g., when resolving symbols for indirect relocations.

Signed-off-by: default avatarEric Ackermann <eric.ackermann@cispa.de>
parent d0a1945f

subsys/llext/llext_link.c

+83 −57
Original line number Diff line number Diff line
@@ -142,6 +142,84 @@ static const void *llext_find_extension_sym(const char *sym_name, struct llext * 
	return se.addr;

}



/**

 * @brief Determine address of a symbol.

 *

 * @param ext llext extension

 * @param ldr llext loader

 * @param link_addr (output) resolved address

 * @param rel relocation entry

 * @param sym symbol entry

 * @param name symbol name

 * @param shdr section header

 *

 * @return 0 for OK, negative for error

 */

static int llext_lookup_symbol(struct llext *ext, struct llext_loader *ldr, uintptr_t *link_addr,

			       const elf_rela_t *rel, const elf_sym_t *sym, const char *name,

			       const elf_shdr_t *shdr)

{

	if (ELF_R_SYM(rel->r_info) == 0) {

		/*

		 * no symbol

		 * example:  R_ARM_V4BX relocation, R_ARM_RELATIVE

		 */

		*link_addr = 0;

	} else if (sym->st_shndx == SHN_UNDEF) {

		/* If symbol is undefined, then we need to look it up */

		*link_addr = (uintptr_t)llext_find_sym(NULL, SYM_NAME_OR_SLID(name, sym->st_value));



		if (*link_addr == 0) {

			/* Try loaded tables */

			struct llext *dep;



			*link_addr = (uintptr_t)llext_find_extension_sym(name, &dep);

			if (*link_addr) {

				llext_dependency_add(ext, dep);

			}

		}



		if (*link_addr == 0) {

			LOG_ERR("Undefined symbol with no entry in "

				"symbol table %s, offset %zd, link section %d",

				name, (size_t)rel->r_offset, shdr->sh_link);

			return -ENODATA;

		}



		LOG_INF("found symbol %s at 0x%lx", name, *link_addr);

	} else if (sym->st_shndx == SHN_ABS) {

		/* Absolute symbol */

		*link_addr = sym->st_value;

	} else if ((sym->st_shndx < ldr->hdr.e_shnum) &&

		   !IN_RANGE(sym->st_shndx, SHN_LORESERVE, SHN_HIRESERVE)) {

		/* This check rejects all relocations whose target symbol has a section index higher

		 * than the maximum possible in this ELF file, or belongs in the reserved range:

		 * they will be caught by the `else` below and cause an error to be returned. This

		 * aborts the LLEXT's loading and prevents execution of improperly relocated code,

		 * which is dangerous.

		 *

		 * Note that the unsupported SHN_COMMON section is rejected as part of this check.

		 * Also note that SHN_ABS would be rejected as well, but we want to handle it

		 * properly: for this reason, this check must come AFTER handling the case where the

		 * symbol's section index is SHN_ABS!

		 *

		 *

		 * For regular symbols, the link address is obtained by adding st_value to the start

		 * address of the section in which the target symbol resides.

		 */

		*link_addr =

			(uintptr_t)llext_loaded_sect_ptr(ldr, ext, sym->st_shndx) + sym->st_value;

	} else {

		LOG_ERR("cannot apply relocation: "

			"target symbol has unexpected section index %d (0x%X)",

			sym->st_shndx, sym->st_shndx);

		return -ENOEXEC;

	}



	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)

{
@@ -407,64 +485,12 @@ int llext_link(struct llext_loader *ldr, struct llext *ext, const struct llext_l 


			op_loc = sect_base + rel.r_offset;



			if (ELF_R_SYM(rel.r_info) == 0) {

				/* no symbol ex: R_ARM_V4BX relocation, R_ARM_RELATIVE  */

				link_addr = 0;

			} else if (sym.st_shndx == SHN_UNDEF) {

				/* If symbol is undefined, then we need to look it up */

				link_addr = (uintptr_t)llext_find_sym(NULL,

					SYM_NAME_OR_SLID(name, sym.st_value));



				if (link_addr == 0) {

					/* Try loaded tables */

					struct llext *dep;



					link_addr = (uintptr_t)llext_find_extension_sym(name, &dep);

					if (link_addr) {

						llext_dependency_add(ext, dep);

					}

				}



				if (link_addr == 0) {

					LOG_ERR("Undefined symbol with no entry in "

						"symbol table %s, offset %zd, link section %d",

						name, (size_t)rel.r_offset, shdr->sh_link);

					return -ENODATA;

				}

			ret = llext_lookup_symbol(ext, ldr, &link_addr, &rel, &sym, name, shdr);



				LOG_INF("found symbol %s at 0x%lx", name, link_addr);

			} else if (sym.st_shndx == SHN_ABS) {

				/* Absolute symbol */

				link_addr = sym.st_value;

			} else if ((sym.st_shndx < ldr->hdr.e_shnum) &&

				!IN_RANGE(sym.st_shndx, SHN_LORESERVE, SHN_HIRESERVE)) {

				/* This check rejects all relocations whose target symbol

				 * has a section index higher than the maximum possible

				 * in this ELF file, or belongs in the reserved range:

				 * they will be caught by the `else` below and cause an

				 * error to be returned. This aborts the LLEXT's loading

				 * and prevents execution of improperly relocated code,

				 * which is dangerous.

				 *

				 * Note that the unsupported SHN_COMMON section is rejected

				 * as part of this check. Also note that SHN_ABS would be

				 * rejected as well, but we want to handle it properly:

				 * for this reason, this check must come AFTER handling

				 * the case where the symbol's section index is SHN_ABS!

				 *

				 *

				 * For regular symbols, the link address is obtained by

				 * adding st_value to the start address of the section

				 * in which the target symbol resides.

				 */

				link_addr = (uintptr_t)llext_loaded_sect_ptr(ldr, ext,

									     sym.st_shndx)

					    + sym.st_value;

			} else {

				LOG_ERR("rela section %d, entry %d: cannot apply relocation: "

					"target symbol has unexpected section index %d (0x%X)",

					i, j, sym.st_shndx, sym.st_shndx);

				return -ENOEXEC;

			if (ret != 0) {

				LOG_ERR("Failed to lookup symbol in rela section %d entry %d!", i,

					j);

				return ret;

			}



			LOG_INF("writing relocation symbol %s type %zd sym %zd at addr 0x%lx "

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