LLEXT: add llext_section_offset() to replace llext_find_section()

Now that section header cache is persistent, it can be used for
finding sections. Add a new function, similar to llext_find_section()
to use it and deprecate llext_find_section().

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

include/zephyr/llext/llext.h

@@ -354,6 +354,22 @@ int arch_elf_relocate(elf_rela_t *rel, uintptr_t loc,
  */
 ssize_t llext_find_section(struct llext_loader *loader, const char *search_name);
 
+/**
+ * @brief Extract ELF section header by name.
+ *
+ * Searches for a section by name in the ELF file and retrieves its full header.
+ *
+ * @param[in] loader Extension loader data and context
+ * @param[in] ext Extension to be searched
+ * @param[in] search_name Section name to search for
+ * @param[out] shdr Buffer for the section header
+ * @retval 0 Success
+ * @retval -ENOTSUP "peek" method not supported
+ * @retval -ENOENT section not found
+ */
+int llext_get_section_header(struct llext_loader *loader, struct llext *ext,
+			     const char *search_name, elf_shdr_t *shdr);
+
 /**
  * @brief Architecture specific function for local binding relocations
  *

subsys/llext/llext.c

@@ -23,6 +23,32 @@ static sys_slist_t _llext_list = SYS_SLIST_STATIC_INIT(&_llext_list);
 
 static struct k_mutex llext_lock = Z_MUTEX_INITIALIZER(llext_lock);
 
+int llext_get_section_header(struct llext_loader *ldr, struct llext *ext, const char *search_name,
+			     elf_shdr_t *shdr)
+{
+	const elf_shdr_t *tmp;
+	unsigned int i;
+
+	for (i = 0, tmp = ext->sect_hdrs;
+	     i < ext->sect_cnt;
+	     i++, tmp++) {
+		const char *name = llext_peek(ldr,
+					      ldr->sects[LLEXT_MEM_SHSTRTAB].sh_offset +
+					      tmp->sh_name);
+
+		if (!name) {
+			return -ENOTSUP;
+		}
+
+		if (!strcmp(name, search_name)) {
+			*shdr = *tmp;
+			return 0;
+		}
+	}
+
+	return -ENOENT;
+}
+
 ssize_t llext_find_section(struct llext_loader *ldr, const char *search_name)
 {
 	elf_shdr_t *shdr;

tests/subsys/llext/simple/src/test_llext_simple.c

@@ -11,6 +11,7 @@
 #if defined(CONFIG_FILE_SYSTEM_LITTLEFS)
 #include <zephyr/fs/littlefs.h>
 #endif
+#include <zephyr/llext/elf.h>
 #include <zephyr/llext/llext.h>
 #include <zephyr/llext/symbol.h>
 #include <zephyr/llext/buf_loader.h>
@@ -411,6 +412,7 @@ ZTEST(llext, test_find_section)
 	struct llext_loader *loader = &buf_loader.loader;
 	struct llext_load_param ldr_parm = LLEXT_LOAD_PARAM_DEFAULT;
 	struct llext *ext = NULL;
+	elf_shdr_t shdr;
 
 	res = llext_load(loader, "find_section", &ext, &ldr_parm);
 	zassert_ok(res, "load should succeed");
@@ -418,6 +420,11 @@ ZTEST(llext, test_find_section)
 	section_ofs = llext_find_section(loader, ".data");
 	zassert_true(section_ofs > 0, "find_section returned %zd", section_ofs);
 
+	res = llext_get_section_header(loader, ext, ".data", &shdr);
+	zassert_ok(res, "get_section_header() should succeed");
+	zassert_equal(shdr.sh_offset, section_ofs,
+		     "different section offset %zd from get_section_header", shdr.sh_offset);
+
 	uintptr_t symbol_ptr = (uintptr_t)llext_find_sym(&ext->exp_tab, "number");
 	uintptr_t section_ptr = (uintptr_t)find_section_ext + section_ofs;