LLEXT: preserve section headers

Move cached section headers to struct llext from struct llext_loader
to preserve them after llext_load() returns.

Signed-off-by: Guennadi Liakhovetski <[email protected]>

Author: lyakh

include/zephyr/llext/llext.h

@@ -120,8 +120,24 @@ struct llext {
 
 	/** Array of extensions, whose symbols this extension accesses */
 	struct llext *dependency[LLEXT_MAX_DEPENDENCIES];
+
+	/** @cond ignore */
+	unsigned int sect_cnt;
+	elf_shdr_t *sect_hdrs;
+	bool sect_hdrs_on_heap;
+	/** @endcond */
 };
 
+static inline const elf_shdr_t *llext_section_headers(const struct llext *ext)
+{
+	return ext->sect_hdrs;
+}
+
+static inline unsigned int llext_section_count(const struct llext *ext)
+{
+	return ext->sect_cnt;
+}
+
 /**
  * @brief Advanced llext_load parameters
  *

include/zephyr/llext/loader.h

@@ -98,10 +98,7 @@ struct llext_loader {
 	/** @cond ignore */
 	elf_ehdr_t hdr;
 	elf_shdr_t sects[LLEXT_MEM_COUNT];
-	elf_shdr_t *sect_hdrs;
-	bool sect_hdrs_on_heap;
 	struct llext_elf_sect_map *sect_map;
-	uint32_t sect_cnt;
 	/** @endcond */
 };
 

subsys/llext/llext.c

@@ -25,10 +25,6 @@ static struct k_mutex llext_lock = Z_MUTEX_INITIALIZER(llext_lock);
 
 ssize_t llext_find_section(struct llext_loader *ldr, const char *search_name)
 {
-	/* Note that this API is used after llext_load(), so the ldr->sect_hdrs
-	 * cache is already freed. A direct search covers all situations.
-	 */
-
 	elf_shdr_t *shdr;
 	unsigned int i;
 	size_t pos;
@@ -253,6 +249,10 @@ int llext_unload(struct llext **ext)
 	*ext = NULL;
 	k_mutex_unlock(&llext_lock);
 
+	if (tmp->sect_hdrs_on_heap) {
+		llext_free(tmp->sect_hdrs);
+	}
+
 	llext_free_regions(tmp);
 	llext_free(tmp->sym_tab.syms);
 	llext_free(tmp->exp_tab.syms);

subsys/llext/llext_link.c

@@ -280,8 +280,8 @@ int llext_link(struct llext_loader *ldr, struct llext *ext, const struct llext_l
 	const char *name;
 	int i, ret;
 
-	for (i = 0; i < ldr->sect_cnt; ++i) {
-		elf_shdr_t *shdr = ldr->sect_hdrs + i;
+	for (i = 0; i < ext->sect_cnt; ++i) {
+		elf_shdr_t *shdr = ext->sect_hdrs + i;
 
 		/* find proper relocation sections */
 		switch (shdr->sh_type) {
@@ -308,7 +308,7 @@ int llext_link(struct llext_loader *ldr, struct llext *ext, const struct llext_l
 			continue;
 		}
 
-		if (shdr->sh_info >= ldr->sect_cnt ||
+		if (shdr->sh_info >= ext->sect_cnt ||
 		    shdr->sh_size % shdr->sh_entsize != 0) {
 			LOG_ERR("Sanity checks failed for section %d "
 				"(info %zd, size %zd, entsize %zd)", i,
@@ -340,7 +340,7 @@ int llext_link(struct llext_loader *ldr, struct llext *ext, const struct llext_l
 				 * section .X to local or global symbols. They point to entries
 				 * in the symbol table, describing respective symbols
 				 */
-				tgt = ldr->sect_hdrs + shdr->sh_info;
+				tgt = ext->sect_hdrs + shdr->sh_info;
 			}
 
 			llext_link_plt(ldr, ext, shdr, ldr_parm, tgt);
@@ -481,8 +481,8 @@ int llext_link(struct llext_loader *ldr, struct llext *ext, const struct llext_l
 
 	/* Detached section caches should be synchronized in place */
 	if (ldr_parm->section_detached) {
-		for (i = 0; i < ldr->sect_cnt; ++i) {
-			elf_shdr_t *shdr = ldr->sect_hdrs + i;
+		for (i = 0; i < ext->sect_cnt; ++i) {
+			elf_shdr_t *shdr = ext->sect_hdrs + i;
 
 			if (ldr_parm->section_detached(shdr)) {
 				void *base = llext_peek(ldr, shdr->sh_offset);

subsys/llext/llext_load.c

@@ -103,29 +103,29 @@ static int llext_load_elf_data(struct llext_loader *ldr, struct llext *ext)
 		return -ENOEXEC;
 	}
 
-	ldr->sect_cnt = ldr->hdr.e_shnum;
+	ext->sect_cnt = ldr->hdr.e_shnum;
 
-	size_t sect_map_sz = ldr->sect_cnt * sizeof(ldr->sect_map[0]);
+	size_t sect_map_sz = ext->sect_cnt * sizeof(ldr->sect_map[0]);
 
 	ldr->sect_map = llext_alloc(sect_map_sz);
 	if (!ldr->sect_map) {
 		LOG_ERR("Failed to allocate section map, size %zu", sect_map_sz);
 		return -ENOMEM;
 	}
-	for (int i = 0; i < ldr->sect_cnt; i++) {
+	for (int i = 0; i < ext->sect_cnt; i++) {
 		ldr->sect_map[i].mem_idx = LLEXT_MEM_COUNT;
 		ldr->sect_map[i].offset = 0;
 	}
 
-	ldr->sect_hdrs = (elf_shdr_t *) llext_peek(ldr, ldr->hdr.e_shoff);
-	if (ldr->sect_hdrs) {
-		ldr->sect_hdrs_on_heap = false;
+	ext->sect_hdrs = (elf_shdr_t *)llext_peek(ldr, ldr->hdr.e_shoff);
+	if (ext->sect_hdrs) {
+		ext->sect_hdrs_on_heap = false;
 	} else {
-		size_t sect_hdrs_sz = ldr->sect_cnt * sizeof(ldr->sect_hdrs[0]);
+		size_t sect_hdrs_sz = ext->sect_cnt * sizeof(ext->sect_hdrs[0]);
 
-		ldr->sect_hdrs_on_heap = true;
-		ldr->sect_hdrs = llext_alloc(sect_hdrs_sz);
-		if (!ldr->sect_hdrs) {
+		ext->sect_hdrs_on_heap = true;
+		ext->sect_hdrs = llext_alloc(sect_hdrs_sz);
+		if (!ext->sect_hdrs) {
 			LOG_ERR("Failed to allocate section headers, size %zu", sect_hdrs_sz);
 			return -ENOMEM;
 		}
@@ -136,7 +136,7 @@ static int llext_load_elf_data(struct llext_loader *ldr, struct llext *ext)
 			return ret;
 		}
 
-		ret = llext_read(ldr, ldr->sect_hdrs, sect_hdrs_sz);
+		ret = llext_read(ldr, ext->sect_hdrs, sect_hdrs_sz);
 		if (ret != 0) {
 			LOG_ERR("Failed to read section headers");
 			return ret;
@@ -149,15 +149,15 @@ static int llext_load_elf_data(struct llext_loader *ldr, struct llext *ext)
 /*
  * Find all relevant string and symbol tables
  */
-static int llext_find_tables(struct llext_loader *ldr)
+static int llext_find_tables(struct llext_loader *ldr, struct llext *ext)
 {
 	int table_cnt, i;
 
 	memset(ldr->sects, 0, sizeof(ldr->sects));
 
 	/* Find symbol and string tables */
-	for (i = 0, table_cnt = 0; i < ldr->sect_cnt && table_cnt < 3; ++i) {
-		elf_shdr_t *shdr = ldr->sect_hdrs + i;
+	for (i = 0, table_cnt = 0; i < ext->sect_cnt && table_cnt < 3; ++i) {
+		elf_shdr_t *shdr = ext->sect_hdrs + i;
 
 		LOG_DBG("section %d at 0x%zx: name %d, type %d, flags 0x%zx, "
 			"addr 0x%zx, size %zd, link %d, info %d",
@@ -216,8 +216,8 @@ static int llext_map_sections(struct llext_loader *ldr, struct llext *ext,
 	int i, j;
 	const char *name;
 
-	for (i = 0; i < ldr->sect_cnt; ++i) {
-		elf_shdr_t *shdr = ldr->sect_hdrs + i;
+	for (i = 0; i < ext->sect_cnt; ++i) {
+		elf_shdr_t *shdr = ext->sect_hdrs + i;
 
 		name = llext_string(ldr, ext, LLEXT_MEM_SHSTRTAB, shdr->sh_name);
 
@@ -437,8 +437,8 @@ static int llext_map_sections(struct llext_loader *ldr, struct llext *ext,
 	 * Calculate each ELF section's offset inside its memory region. This
 	 * is done as a separate pass so the final regions are already defined.
 	 */
-	for (i = 0; i < ldr->sect_cnt; ++i) {
-		elf_shdr_t *shdr = ldr->sect_hdrs + i;
+	for (i = 0; i < ext->sect_cnt; ++i) {
+		elf_shdr_t *shdr = ext->sect_hdrs + i;
 		enum llext_mem mem_idx = ldr->sect_map[i].mem_idx;
 
 		if (mem_idx != LLEXT_MEM_COUNT) {
@@ -585,7 +585,7 @@ static int llext_copy_symbols(struct llext_loader *ldr, struct llext *ext,
 
 			sym_tab->syms[j].name = name;
 
-			elf_shdr_t *shdr = ldr->sect_hdrs + shndx;
+			elf_shdr_t *shdr = ext->sect_hdrs + shndx;
 			uintptr_t section_addr = shdr->sh_addr;
 
 			if (ldr_parm->pre_located &&
@@ -664,7 +664,7 @@ int do_llext_load(struct llext_loader *ldr, struct llext *ext,
 #endif
 
 	LOG_DBG("Finding ELF tables...");
-	ret = llext_find_tables(ldr);
+	ret = llext_find_tables(ldr, ext);
 	if (ret != 0) {
 		LOG_ERR("Failed to find important ELF tables, ret %d", ret);
 		goto out;
@@ -736,11 +736,6 @@ int do_llext_load(struct llext_loader *ldr, struct llext *ext,
 	llext_free(ldr->sect_map);
 	ldr->sect_map = NULL;
 
-	if (ldr->sect_hdrs_on_heap) {
-		llext_free(ldr->sect_hdrs);
-	}
-	ldr->sect_hdrs = NULL;
-
 	/* Until proper inter-llext linking is implemented, the symbol table is
 	 * not useful outside of the loading process; keep it only if debugging
 	 * is enabled and no error is detected.