LLEXT: fix a needless allocation

When CONFIG_LLEXT_STORAGE_WRITABLE is selected and .pre_located is
set, the BSS section is allocated by the user too, no need to
allocate it internally.

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

Author: lyakh

include/zephyr/llext/llext.h

@@ -132,7 +132,10 @@ struct llext_load_param {
 	bool relocate_local;
 	/**
 	 * Use the virtual symbol addresses from the ELF, not addresses within
-	 * the memory buffer, when calculating relocation targets.
+	 * the memory buffer, when calculating relocation targets. It also
+	 * means, that the application will take care to place the extension at
+	 * those pre-defined addresses, so the LLEXT core doesn't have to do any
+	 * allocation and copying internally.
 	 */
 	bool pre_located;
 	/**

subsys/llext/llext_load.c

@@ -684,7 +684,7 @@ int do_llext_load(struct llext_loader *ldr, struct llext *ext,
 	}
 
 	LOG_DBG("Allocate and copy regions...");
-	ret = llext_copy_regions(ldr, ext);
+	ret = llext_copy_regions(ldr, ext, ldr_parm);
 	if (ret != 0) {
 		LOG_ERR("Failed to copy regions, ret %d", ret);
 		goto out;

subsys/llext/llext_mem.c

@@ -59,7 +59,7 @@ static void llext_init_mem_part(struct llext *ext, enum llext_mem mem_idx,
 }
 
 static int llext_copy_section(struct llext_loader *ldr, struct llext *ext,
-			      enum llext_mem mem_idx)
+			      enum llext_mem mem_idx, const struct llext_load_param *ldr_parm)
 {
 	int ret;
 
@@ -68,18 +68,31 @@ static int llext_copy_section(struct llext_loader *ldr, struct llext *ext,
 	}
 	ext->mem_size[mem_idx] = ldr->sects[mem_idx].sh_size;
 
-	if (ldr->sects[mem_idx].sh_type != SHT_NOBITS &&
-	    IS_ENABLED(CONFIG_LLEXT_STORAGE_WRITABLE)) {
-		/* Directly use data from the ELF buffer if peek() is supported */
-		ext->mem[mem_idx] = llext_peek(ldr, ldr->sects[mem_idx].sh_offset);
-		if (ext->mem[mem_idx]) {
-			llext_init_mem_part(ext, mem_idx, (uintptr_t)ext->mem[mem_idx],
-				ldr->sects[mem_idx].sh_size);
+	if (IS_ENABLED(CONFIG_LLEXT_STORAGE_WRITABLE)) {
+		if (ldr->sects[mem_idx].sh_type != SHT_NOBITS) {
+			/* Directly use data from the ELF buffer if peek() is supported */
+			ext->mem[mem_idx] = llext_peek(ldr, ldr->sects[mem_idx].sh_offset);
+			if (ext->mem[mem_idx]) {
+				llext_init_mem_part(ext, mem_idx, (uintptr_t)ext->mem[mem_idx],
+						    ldr->sects[mem_idx].sh_size);
+				ext->mem_on_heap[mem_idx] = false;
+				return 0;
+			}
+		} else if (ldr_parm && ldr_parm->pre_located) {
+			/*
+			 * ldr_parm cannot be NULL here with the current flow, but
+			 * we add a check to make it future-proof
+			 */
+			ext->mem[mem_idx] = NULL;
 			ext->mem_on_heap[mem_idx] = false;
 			return 0;
 		}
 	}
 
+	if (ldr_parm && ldr_parm->pre_located) {
+		return -EFAULT;
+	}
+
 	/* On ARM with an MPU a pow(2, N)*32 sized and aligned region is needed,
 	 * otherwise its typically an mmu page (sized and aligned memory region)
 	 * we are after that we can assign memory permission bits on.
@@ -132,24 +145,25 @@ static int llext_copy_section(struct llext_loader *ldr, struct llext *ext,
 
 int llext_copy_strings(struct llext_loader *ldr, struct llext *ext)
 {
-	int ret = llext_copy_section(ldr, ext, LLEXT_MEM_SHSTRTAB);
+	int ret = llext_copy_section(ldr, ext, LLEXT_MEM_SHSTRTAB, NULL);
 
 	if (!ret) {
-		ret = llext_copy_section(ldr, ext, LLEXT_MEM_STRTAB);
+		ret = llext_copy_section(ldr, ext, LLEXT_MEM_STRTAB, NULL);
 	}
 
 	return ret;
 }
 
-int llext_copy_regions(struct llext_loader *ldr, struct llext *ext)
+int llext_copy_regions(struct llext_loader *ldr, struct llext *ext,
+		       const struct llext_load_param *ldr_parm)
 {
 	for (enum llext_mem mem_idx = 0; mem_idx < LLEXT_MEM_COUNT; mem_idx++) {
 		/* strings have already been copied */
 		if (ext->mem[mem_idx]) {
 			continue;
 		}
 
-		int ret = llext_copy_section(ldr, ext, mem_idx);
+		int ret = llext_copy_section(ldr, ext, mem_idx, ldr_parm);
 
 		if (ret < 0) {
 			return ret;

subsys/llext/llext_priv.h

@@ -20,7 +20,8 @@ struct llext_elf_sect_map {
  */
 
 int llext_copy_strings(struct llext_loader *ldr, struct llext *ext);
-int llext_copy_regions(struct llext_loader *ldr, struct llext *ext);
+int llext_copy_regions(struct llext_loader *ldr, struct llext *ext,
+		       const struct llext_load_param *ldr_parm);
 void llext_free_regions(struct llext *ext);
 void llext_adjust_mmu_permissions(struct llext *ext);