llext: add a function for finding ELF sections

Applications can use custom ELF sections for their own purposes, add
a function for finding them.

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

include/zephyr/llext/llext.h

@@ -142,6 +142,15 @@ 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 Find an ELF section
+ *
+ * @param loader Extension loader data and context
+ * @param search_name Section name to search for
+ * @retval Section offset or a negative error code
+ */
+ssize_t llext_find_section(struct llext_loader *loader, const char *search_name);
+
 /**
  * @brief Architecture specific function for updating addresses via relocation table
  *

subsys/llext/llext.c

@@ -47,6 +47,33 @@ sys_slist_t *llext_list(void)
 	return &_llext_list;
 }
 
+ssize_t llext_find_section(struct llext_loader *ldr, const char *search_name)
+{
+	elf_shdr_t *shdr;
+	unsigned int i;
+	size_t pos;
+
+	for (i = 0, pos = ldr->hdr.e_shoff;
+	     i < ldr->hdr.e_shnum;
+	     i++, pos += ldr->hdr.e_shentsize) {
+		shdr = llext_peek(ldr, pos);
+		if (!shdr) {
+			/* The peek() method isn't supported */
+			return -EOPNOTSUPP;
+		}
+
+		const char *name = llext_peek(ldr,
+					      ldr->sects[LLEXT_SECT_SHSTRTAB].sh_offset +
+					      shdr->sh_name);
+
+		if (!strcmp(name, search_name)) {
+			return shdr->sh_offset;
+		}
+	}
+
+	return -ENOENT;
+}
+
 struct llext *llext_by_name(const char *name)
 {
 	sys_slist_t *mlist = llext_list();