Index: llvm/docs/CommandGuide/llvm-objdump.rst
===================================================================
--- llvm/docs/CommandGuide/llvm-objdump.rst
+++ llvm/docs/CommandGuide/llvm-objdump.rst
@@ -11,10 +11,9 @@
 DESCRIPTION
 -----------
 The :program:`llvm-objdump` utility prints the contents of object files and
-final linked images named on the command line. If no file name is specified,
-:program:`llvm-objdump` will attempt to read from *a.out*. If *-* is used as a
-file name, :program:`llvm-objdump` will process a file on its standard input
-stream.
+final linked images named on the command line. If no filename is specified,
+or *-* is used as a filename, :program:`llvm-objdump` will read a file from
+its standard input stream.
 
 COMMANDS
 --------
Index: llvm/test/tools/llvm-objdump/stdin.test
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-objdump/stdin.test
@@ -0,0 +1,45 @@
+## Test llvm-objdump when using stdin both explicitly (using '-' as a filename)
+## and implicitly (not specifying any filename).
+
+# RUN: yaml2obj %s > a.out
+
+## This will fail because llvm-lit redirects to stdin by default, it will be
+## read but is not a valid object file, test that it fails because of this
+## and does not use a.out as the default file.
+# RUN: not llvm-objdump -h 2>&1 | FileCheck %s
+# CHECK-NOT: error: 'a.out': No such file or directory
+
+## This is a hack to get the base output to use the filename '<stdin>' which
+## is used as the filename in the llvm-objdumps output when reading a file
+## from standard input.
+# RUN: cp a.out \<stdin\>
+
+## Pass an explicit filename to produce a baseline output. llvm-objdump should
+## have the same behavior when opening a file itself and when reading that
+## file from its standard input stream.
+# RUN: llvm-objdump -h \<stdin\> > %t.base 2> %t.err
+# RUN: FileCheck %s --input-file=%t.err --allow-empty --implicit-check-not={{.}}
+
+# RUN: llvm-objdump -h - < a.out > %t.explicit 2> %t.err
+# RUN: FileCheck %s --input-file=%t.err --allow-empty --implicit-check-not={{.}}
+# UN: cmp %t.base %t.explicit
+
+# RUN: llvm-objdump -h < a.out > %t.implicit 2> %t.err
+# RUN: FileCheck %s --input-file=%t.err --allow-empty --implicit-check-not={{.}}
+# RUN: cmp %t.base %t.implicit
+
+# RUN: rm -f a.out \<stdin\>
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+Sections:
+  - Name:         .text
+    Type:         SHT_PROGBITS
+    Flags:        [SHF_ALLOC, SHF_EXECINSTR]
+    Address:      0x400
+    AddressAlign: 0x10
+    Content:      'c3'
Index: llvm/tools/llvm-objdump/llvm-objdump.cpp
===================================================================
--- llvm/tools/llvm-objdump/llvm-objdump.cpp
+++ llvm/tools/llvm-objdump/llvm-objdump.cpp
@@ -55,6 +55,7 @@
 #include "llvm/Support/Host.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Process.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/StringSaver.h"
 #include "llvm/Support/TargetRegistry.h"
@@ -2107,6 +2108,12 @@
 
 /// Open file and figure out how to dump it.
 static void dumpInput(StringRef file) {
+  if (file == "-" && sys::Process::StandardInIsUserInput()) {
+    WithColor::warning(errs(), ToolName) << "can't read from terminal\n";
+    cl::PrintHelpMessage();
+    exit(1);
+  }
+
   // If we are using the Mach-O specific object file parser, then let it parse
   // the file and process the command line options.  So the -arch flags can
   // be used to select specific slices, etc.
@@ -2151,9 +2158,9 @@
 
   ToolName = argv[0];
 
-  // Defaults to a.out if no filenames specified.
+  // Defaults to stdin if no filenames are specified.
   if (InputFilenames.empty())
-    InputFilenames.push_back("a.out");
+    InputFilenames.push_back("-");
 
   if (AllHeaders)
     ArchiveHeaders = FileHeaders = PrivateHeaders = Relocations =