elf: Add function to read section content with allocation

In many functions there is need to read user section content
and check firmware version or write section content to some
manifest or dictionary. Previously to do it, in each function
was loop to search for proper section in proper module,
then allocate buffer, read content and check for possible error
between each step what is quite overwhelming. After change there
will be one function responsible for this task.

Signed-off-by: Karol Trzcinski <karolx.trzcinski@linux.intel.com>

src/elf.c

@@ -516,6 +516,52 @@ out:
 	return ret;
 }
 
+int elf_read_section(const struct image *image, const char *section_name,
+		     const Elf32_Shdr **dst_section, void **dst_buff)
+{
+	const struct module *module;
+	const Elf32_Shdr *section;
+	int section_index = -1;
+	int read;
+	int i;
+
+	/* when there is more than one module, then first one is bootloader */
+	for (i = image->num_modules == 1 ? 0 : 1; i < image->num_modules; i++) {
+		module = &image->module[i];
+		section_index = elf_find_section(module, section_name);
+		if (section_index >= 0)
+			break;
+	}
+
+	if (section_index < 0) {
+		fprintf(stderr, "error: section %s can't be found\n",
+			section_name);
+		return -EINVAL;
+	}
+
+	section = &module->section[section_index];
+	if (dst_section)
+		*dst_section = section;
+
+	/* alloc buffer for section content */
+	*dst_buff = calloc(1, section->size);
+	if (!*dst_buff)
+		return -ENOMEM;
+
+	/* fill buffer with section content */
+	fseek(module->fd, section->off, SEEK_SET);
+	read = fread(*dst_buff, 1, section->size, module->fd);
+	if (read != section->size) {
+		fprintf(stderr,
+			"error: can't read %s section %d\n", section_name,
+			-errno);
+		free(*dst_buff);
+		return -errno;
+	}
+
+	return section->size;
+}
+
 int elf_parse_module(struct image *image, int module_index, const char *name)
 {
 	struct module *module;

src/include/rimage/rimage.h

@@ -177,6 +177,8 @@ void elf_free_module(struct image *image, int module_index);
 int elf_is_rom(struct image *image, Elf32_Shdr *section);
 int elf_validate_modules(struct image *image);
 int elf_find_section(const struct module *module, const char *name);
+int elf_read_section(const struct image *image, const char *name,
+		     const Elf32_Shdr **dst_section, void **dst_buff);
 int elf_validate_section(struct image *image, struct module *module,
 			 Elf32_Shdr *section, int index);