llext: add option to keep section data after llext_load

This is required for the functions that inspect the ELF file to work
properly. The user must then call llext_free_inspection_data() before
calling llext_unload() to free the memory left allocated in the loader
and extension memory.

Signed-off-by: Luca Burelli <[email protected]>

Author: pillo79

include/zephyr/llext/llext.h

@@ -146,6 +146,7 @@ static inline unsigned int llext_section_count(const struct llext *ext)
 struct llext_load_param {
 	/** Perform local relocation */
 	bool relocate_local;
+
 	/**
 	 * Use the virtual symbol addresses from the ELF, not addresses within
 	 * the memory buffer, when calculating relocation targets. It also
@@ -154,12 +155,22 @@ struct llext_load_param {
 	 * allocation and copying internally.
 	 */
 	bool pre_located;
+
 	/**
 	 * Extensions can implement custom ELF sections to be loaded in specific
 	 * memory regions, detached from other sections of compatible types.
 	 * This optional callback checks whether a section should be detached.
 	 */
 	bool (*section_detached)(const elf_shdr_t *shdr);
+
+	/**
+	 * Keep the ELF section data in memory after loading the extension. This
+	 * is needed to use some of the functions in @ref llext_inspect_apis.
+	 *
+	 * @note Related memory must be freed by @ref llext_free_inspection_data
+	 *       before the extension can be unloaded via @ref llext_unload.
+	 */
+	bool keep_section_info;
 };
 
 /** Default initializer for @ref llext_load_param */
@@ -211,6 +222,19 @@ int llext_load(struct llext_loader *loader, const char *name, struct llext **ext
  */
 int llext_unload(struct llext **ext);
 
+/**
+ * @brief Free any inspection-related memory for the specified loader and extension.
+ *
+ * This is only required if inspection data was requested at load time by
+ * setting @ref llext_load_param.keep_section_info; otherwise, this call will
+ * be a no-op.
+ *
+ * @param[in] ldr Extension loader
+ * @param[in] ext Extension
+ * @returns 0 on success, or a negative error code.
+ */
+int llext_free_inspection_data(struct llext_loader *ldr, struct llext *ext);
+
 /** @brief Entry point function signature for an extension. */
 typedef void (*llext_entry_fn_t)(void *user_data);
 

subsys/llext/llext_load.c

@@ -112,6 +112,7 @@ static int llext_load_elf_data(struct llext_loader *ldr, struct llext *ext)
 		LOG_ERR("Failed to allocate section map, size %zu", sect_map_sz);
 		return -ENOMEM;
 	}
+	ext->alloc_size += sect_map_sz;
 	for (int i = 0; i < ext->sect_cnt; i++) {
 		ldr->sect_map[i].mem_idx = LLEXT_MEM_COUNT;
 		ldr->sect_map[i].offset = 0;
@@ -759,12 +760,13 @@ int do_llext_load(struct llext_loader *ldr, struct llext *ext,
 
 out:
 	/*
-	 * Free resources only used during loading. Note that this exploits
-	 * the fact that freeing a NULL pointer has no effect.
+	 * Free resources only used during loading, unless explicitly requested.
+	 * Note that this exploits the fact that freeing a NULL pointer has no effect.
 	 */
 
-	llext_free(ldr->sect_map);
-	ldr->sect_map = NULL;
+	if (ret != 0 || !ldr_parm || !ldr_parm->keep_section_info) {
+		llext_free_inspection_data(ldr, ext);
+	}
 
 	/* Until proper inter-llext linking is implemented, the symbol table is
 	 * not useful outside of the loading process; keep it only if debugging
@@ -796,3 +798,14 @@ int do_llext_load(struct llext_loader *ldr, struct llext *ext,
 
 	return ret;
 }
+
+int llext_free_inspection_data(struct llext_loader *ldr, struct llext *ext)
+{
+	if (ldr->sect_map) {
+		ext->alloc_size -= ext->sect_cnt * sizeof(ldr->sect_map[0]);
+		llext_free(ldr->sect_map);
+		ldr->sect_map = NULL;
+	}
+
+	return 0;
+}