test bswap_32 handling

Author: theihor

tools/bpf/resolve_btfids/main.c

@@ -348,6 +348,18 @@ static int compressed_section_fix(Elf *elf, Elf_Scn *scn, GElf_Shdr *sh)
 	return 0;
 }
 
+static void bswap_32_data(void* data, u32 nr_bytes)
+{
+	u32 cnt, i;
+	u32 *ptr;
+
+	cnt = nr_bytes / sizeof(u32);
+	ptr = data;
+
+	for (i = 0; i < cnt; i++)
+		ptr[i] = bswap_32(ptr[i]);
+}
+
 static int elf_collect(struct object *obj)
 {
 	Elf_Scn *scn = NULL;
@@ -429,6 +441,16 @@ static int elf_collect(struct object *obj)
 			obj->efile.symbols_shndx = idx;
 			obj->efile.strtabidx     = sh.sh_link;
 		} else if (!strcmp(name, BTF_IDS_SECTION)) {
+			/*
+			* If target endianness differs from host, we need to bswap32
+			* the .BTF_ids section data on load, because .BTF_ids has
+			* Elf_Type = ELF_T_BYTE, and so libelf returns data buffer in
+			* the target endiannes. We repeat this on dump.
+			*/
+			if (obj->efile.encoding != ELFDATANATIVE) {
+				pr_debug("bswap_32 .BTF_ids data from target to host endianness\n");
+				bswap_32_data(data->d_buf, data->d_size);
+			}
 			obj->efile.idlist       = data;
 			obj->efile.idlist_shndx = idx;
 			obj->efile.idlist_addr  = sh.sh_addr;
@@ -751,22 +773,6 @@ static int sets_patch(struct object *obj)
 			 */
 			BUILD_BUG_ON((u32 *)set8->pairs != &set8->pairs[0].id);
 			qsort(set8->pairs, set8->cnt, sizeof(set8->pairs[0]), cmp_id);
-
-			/*
-			 * When ELF endianness does not match endianness of the
-			 * host, we have to make sure SET8 flags are not byteswapped
-			 * on dump, because they are already in the target endianness.
-			 * So we bswap them here to the host endiannes.
-			 */
-			if (obj->efile.encoding != ELFDATANATIVE) {
-				int i;
-
-				set8->flags = bswap_32(set8->flags);
-				for (i = 0; i < set8->cnt; i++) {
-					set8->pairs[i].flags =
-						bswap_32(set8->pairs[i].flags);
-				}
-			}
 			break;
 		case BTF_ID_KIND_SYM:
 		default:
@@ -823,27 +829,21 @@ static int dump_raw_data(const char *out_path, const void *data, u32 size)
 static int dump_raw_btf_ids(struct object *obj, const char *out_path)
 {
 	Elf_Data *data = obj->efile.idlist;
-	int fd, err, i, cnt;
-	u32 *ptr;
+	int fd, err;
 
 	if (!data || !data->d_buf) {
 		pr_debug("%s has no BTF_ids data to dump\n", obj->path);
 		return 0;
 	}
 
 	/*
-	 * If target endianness differs from host, we need to byteswap
-	 * all the u32 values in the .BTF_ids section before dumping,
-	 * because elf_getdata() converts to host endianness and
-	 * objcopy --update-section does a raw byte copy.
+	 * If target endianness differs from host, we need to bswap32 the
+	 * .BTF_ids section data before dumping so that the output is in
+	 * target endianness.
 	 */
 	if (obj->efile.encoding != ELFDATANATIVE) {
-		cnt = data->d_size / sizeof(u32);
-		ptr = data->d_buf;
-
 		pr_debug("bswap_32 .BTF_ids data from host to target endianness\n");
-		for (i = 0; i < cnt; i++)
-			ptr[i] = bswap_32(ptr[i]);
+		bswap_32_data(data->d_buf, data->d_size);
 	}
 
 	err = dump_raw_data(out_path, data->d_buf, data->d_size);