libbpf: streamline ELF parsing error-handling

Simplify ELF parsing logic by exiting early, as there is no common clean
up path to execute. That makes it unnecessary to track when err was set
and when it was cleared. It also reduces nesting in some places.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/lib/bpf/libbpf.c

@@ -1154,24 +1154,21 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
 		if (gelf_getshdr(scn, &sh) != &sh) {
 			pr_warning("failed to get section(%d) header from %s\n",
 				   idx, obj->path);
-			err = -LIBBPF_ERRNO__FORMAT;
-			goto out;
+			return -LIBBPF_ERRNO__FORMAT;
 		}
 
 		name = elf_strptr(elf, ep->e_shstrndx, sh.sh_name);
 		if (!name) {
 			pr_warning("failed to get section(%d) name from %s\n",
 				   idx, obj->path);
-			err = -LIBBPF_ERRNO__FORMAT;
-			goto out;
+			return -LIBBPF_ERRNO__FORMAT;
 		}
 
 		data = elf_getdata(scn, 0);
 		if (!data) {
 			pr_warning("failed to get section(%d) data from %s(%s)\n",
 				   idx, name, obj->path);
-			err = -LIBBPF_ERRNO__FORMAT;
-			goto out;
+			return -LIBBPF_ERRNO__FORMAT;
 		}
 		pr_debug("section(%d) %s, size %ld, link %d, flags %lx, type=%d\n",
 			 idx, name, (unsigned long)data->d_size,
@@ -1182,10 +1179,14 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
 			err = bpf_object__init_license(obj,
 						       data->d_buf,
 						       data->d_size);
+			if (err)
+				return err;
 		} else if (strcmp(name, "version") == 0) {
 			err = bpf_object__init_kversion(obj,
 							data->d_buf,
 							data->d_size);
+			if (err)
+				return err;
 		} else if (strcmp(name, "maps") == 0) {
 			obj->efile.maps_shndx = idx;
 		} else if (strcmp(name, BTF_ELF_SEC) == 0) {
@@ -1196,11 +1197,10 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
 			if (obj->efile.symbols) {
 				pr_warning("bpf: multiple SYMTAB in %s\n",
 					   obj->path);
-				err = -LIBBPF_ERRNO__FORMAT;
-			} else {
-				obj->efile.symbols = data;
-				obj->efile.strtabidx = sh.sh_link;
+				return -LIBBPF_ERRNO__FORMAT;
 			}
+			obj->efile.symbols = data;
+			obj->efile.strtabidx = sh.sh_link;
 		} else if (sh.sh_type == SHT_PROGBITS && data->d_size > 0) {
 			if (sh.sh_flags & SHF_EXECINSTR) {
 				if (strcmp(name, ".text") == 0)
@@ -1214,6 +1214,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
 
 					pr_warning("failed to alloc program %s (%s): %s",
 						   name, obj->path, cp);
+					return err;
 				}
 			} else if (strcmp(name, ".data") == 0) {
 				obj->efile.data = data;
@@ -1225,8 +1226,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
 				pr_debug("skip section(%d) %s\n", idx, name);
 			}
 		} else if (sh.sh_type == SHT_REL) {
+			int nr_reloc = obj->efile.nr_reloc;
 			void *reloc = obj->efile.reloc;
-			int nr_reloc = obj->efile.nr_reloc + 1;
 			int sec = sh.sh_info; /* points to other section */
 
 			/* Only do relo for section with exec instructions */
@@ -1236,28 +1237,24 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
 				continue;
 			}
 
-			reloc = reallocarray(reloc, nr_reloc,
+			reloc = reallocarray(reloc, nr_reloc + 1,
 					     sizeof(*obj->efile.reloc));
 			if (!reloc) {
 				pr_warning("realloc failed\n");
-				err = -ENOMEM;
-			} else {
-				int n = nr_reloc - 1;
+				return -ENOMEM;
+			}
 
-				obj->efile.reloc = reloc;
-				obj->efile.nr_reloc = nr_reloc;
+			obj->efile.reloc = reloc;
+			obj->efile.nr_reloc++;
 
-				obj->efile.reloc[n].shdr = sh;
-				obj->efile.reloc[n].data = data;
-			}
+			obj->efile.reloc[nr_reloc].shdr = sh;
+			obj->efile.reloc[nr_reloc].data = data;
 		} else if (sh.sh_type == SHT_NOBITS && strcmp(name, ".bss") == 0) {
 			obj->efile.bss = data;
 			obj->efile.bss_shndx = idx;
 		} else {
 			pr_debug("skip section(%d) %s\n", idx, name);
 		}
-		if (err)
-			goto out;
 	}
 
 	if (!obj->efile.strtabidx || obj->efile.strtabidx >= idx) {
@@ -1270,10 +1267,9 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
 	if (bpf_object__has_maps(obj)) {
 		err = bpf_object__init_maps(obj, flags);
 		if (err)
-			goto out;
+			return err;
 	}
 	err = bpf_object__init_prog_names(obj);
-out:
 	return err;
 }