scripts: Adopted better input file handling in result scripts

- Error on no/insufficient files.

  Instead of just returning no results. This is more useful when
  debugging complicated bash scripts.

- Use elf magic to allow any file order in perfbd.py/stack.py.

  This was already implemented in stack.py, now also adopted in
  perfbd.py.

  Elf files always start with the magic string "\x7fELF", so we can use
  this to figure out the types of input files without needing to rely on
  argument order.

  This is just one less thing to worry about when invoking these
  scripts.

scripts/perfbd.py

@@ -170,6 +170,11 @@ def openio(path, mode='r', buffering=-1):
     else:
         return open(path, mode, buffering)
 
+def iself(path):
+    # check for an elf file's magic string (\x7fELF)
+    with open(path, 'rb') as f:
+        return f.read(4) == b'\x7fELF'
+
 class Sym(co.namedtuple('Sym', [
         'name', 'global_', 'section', 'addr', 'size'])):
     __slots__ = ()
@@ -714,7 +719,7 @@ def starapply(args):
     f, args, kwargs = args
     return f(*args, **kwargs)
 
-def collect(obj_path, trace_paths, *,
+def collect(elf_path, trace_paths, *,
         jobs=None,
         **args):
     # automatic job detection?
@@ -722,10 +727,10 @@ def collect(obj_path, trace_paths, *,
         jobs = len(os.sched_getaffinity(0))
 
     # find sym/line info to reverse ASLR
-    syms = collect_syms(obj_path,
+    syms = collect_syms(elf_path,
             sections=['.text'],
             **args)
-    lines = collect_dwarf_lines(obj_path, **args)
+    lines = collect_dwarf_lines(elf_path, **args)
 
     if jobs is not None:
         # try to split up files so that even single files can be processed
@@ -1265,7 +1270,7 @@ def annotate(Result, results, *,
                 print(line)
 
 
-def report(obj_path='', trace_paths=[], *,
+def report(paths, *,
         by=None,
         fields=None,
         defines=[],
@@ -1287,7 +1292,32 @@ def report(obj_path='', trace_paths=[], *,
 
     # find sizes
     if not args.get('use', None):
-        results = collect(obj_path, trace_paths, **args)
+        # figure out paths
+        elf_paths = []
+        trace_paths = []
+        for path in paths:
+            if iself(path):
+                elf_paths.append(path)
+            else:
+                trace_paths.append(path)
+        # not enough info?
+        if not elf_paths:
+            print("error: no elf file?",
+                    file=sys.stderr)
+            sys.exit(1)
+        if not trace_paths:
+            print("error: no *.trace files?",
+                    file=sys.stderr)
+            sys.exit(1)
+        # too much info?
+        if len(elf_paths) != 1:
+            print("error: multiple elf files?",
+                    file=sys.stderr)
+            sys.exit(1)
+
+        # collect info
+        results = collect(elf_paths[0], trace_paths, **args)
+
     else:
         results = []
         with openio(args['use']) as f:
@@ -1400,13 +1430,25 @@ if __name__ == "__main__":
             description="Aggregate and report call-stack propagated "
                 "block-device operations from trace output.",
             allow_abbrev=False)
+    class AppendPath(argparse.Action):
+        def __call__(self, parser, namespace, value, option):
+            if getattr(namespace, 'paths', None) is None:
+                namespace.paths = []
+            if value is None:
+                pass
+            elif isinstance(value, str):
+                namespace.paths.append(value)
+            else:
+                namespace.paths.extend(value)
     parser.add_argument(
-            'obj_path',
+            'elf_path',
             nargs='?',
+            action=AppendPath,
             help="Input executable for mapping addresses to symbols.")
     parser.add_argument(
             'trace_paths',
             nargs='*',
+            action=AppendPath,
             help="Input *.trace files.")
     parser.add_argument(
             '-v', '--verbose',