llext: Add new methods to loader API

Introducing `llext_prepare()` and `llext_finalize()` APIs
that are invoked and the beginning and the end of the `llext_load()`
function.

The purpose of these functions is to bring possibility of initializing
loader before it is used and uninitialize or clean up when
it is no longer needed. Both functions are optional.

The buffer loader has been aligned to methods introduced in the patch.

Signed-off-by: Adam Wojasinski <[email protected]>

Author: awojasinski

include/zephyr/llext/buf_loader.h

@@ -47,16 +47,19 @@ void *llext_buf_peek(struct llext_loader *ldr, size_t pos);
  * @param _buf Buffer containing the ELF binary
  * @param _buf_len Buffer length in bytes
  */
-#define LLEXT_BUF_LOADER(_buf, _buf_len)		\
-	{						\
-		.loader = {				\
-			.read = llext_buf_read,		\
-			.seek = llext_buf_seek,		\
-			.peek = llext_buf_peek,		\
-		},					\
-		.buf = (_buf),				\
-		.len = (_buf_len),			\
-		.pos = 0				\
+#define LLEXT_BUF_LOADER(_buf, _buf_len)                                                           \
+	{                                                                                          \
+		.loader =                                                                          \
+			{                                                                          \
+				.prepare = NULL,                                                   \
+				.read = llext_buf_read,                                            \
+				.seek = llext_buf_seek,                                            \
+				.peek = llext_buf_peek,                                            \
+				.finalize = NULL,                                                  \
+			},                                                                         \
+		.buf = (_buf),                                                                     \
+		.len = (_buf_len),                                                                 \
+		.pos = 0,                                                                          \
 	}
 
 /**

include/zephyr/llext/loader.h

@@ -40,6 +40,15 @@ struct llext_elf_sect_map; /* defined in llext_priv.h */
  * extension is loaded, this object is no longer needed.
  */
 struct llext_loader {
+	/**
+	 * @brief Optional function to prepare the loader for loading extension.
+	 *
+	 * @param[in] ldr Loader
+	 *
+	 * @returns 0 on success, or a negative error.
+	 */
+	int (*prepare)(struct llext_loader *ldr);
+
 	/**
 	 * @brief Function to read (copy) from the loader
 	 *
@@ -79,6 +88,13 @@ struct llext_loader {
 	 */
 	void *(*peek)(struct llext_loader *ldr, size_t pos);
 
+	/**
+	 * @brief Optional function to clean after the extension has been loaded or error occurred.
+	 *
+	 * @param[in] ldr Loader
+	 */
+	void (*finalize)(struct llext_loader *ldr);
+
 	/** @cond ignore */
 	elf_ehdr_t hdr;
 	elf_shdr_t sects[LLEXT_MEM_COUNT];
@@ -90,6 +106,15 @@ struct llext_loader {
 };
 
 /** @cond ignore */
+static inline int llext_prepare(struct llext_loader *l)
+{
+	if (l->prepare) {
+		return l->prepare(l);
+	}
+
+	return 0;
+}
+
 static inline int llext_read(struct llext_loader *l, void *buf, size_t len)
 {
 	return l->read(l, buf, len);
@@ -108,6 +133,13 @@ static inline void *llext_peek(struct llext_loader *l, size_t pos)
 
 	return NULL;
 }
+
+static inline void llext_finalize(struct llext_loader *l)
+{
+	if (l->finalize) {
+		l->finalize(l);
+	}
+}
 /* @endcond */
 
 /**

subsys/llext/llext_load.c

@@ -556,6 +556,12 @@ int do_llext_load(struct llext_loader *ldr, struct llext *ext,
 	ldr->sect_map = NULL;
 
 	LOG_DBG("Loading ELF data...");
+	ret = llext_prepare(ldr);
+	if (ret != 0) {
+		LOG_ERR("Failed to prepare the loader, ret %d", ret);
+		goto out;
+	}
+
 	ret = llext_load_elf_data(ldr, ext);
 	if (ret != 0) {
 		LOG_ERR("Failed to load basic ELF data, ret %d", ret);
@@ -674,5 +680,7 @@ int do_llext_load(struct llext_loader *ldr, struct llext *ext,
 			ext->mem[LLEXT_MEM_RODATA]);
 	}
 
+	llext_finalize(ldr);
+
 	return ret;
 }