Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -42,6 +42,7 @@
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Object/Decompressor.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/TarWriter.h"
 #include "llvm/Support/TargetSelect.h"
@@ -529,6 +530,17 @@
   return Ret;
 }
 
+static void ensureWritable(StringRef Path, StringRef FileDecsription) {
+  if (Path.empty())
+    return;
+
+  std::error_code EC;
+  raw_fd_ostream OS(Path, EC, sys::fs::F_Append);
+  if (EC)
+    error("cannot write to " + FileDecsription + " " + Path + ": " +
+          EC.message());
+}
+
 // Initializes Config members by the command line options.
 void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   Config->AllowMultipleDefinition = Args.hasArg(OPT_allow_multiple_definition);
@@ -617,9 +629,17 @@
     Config->Emulation = S;
   }
 
+  // Fail early if output files are not writable. If a user has a long link,
+  // e.g. due to a large LTO link, they do not wish to run it and find that it
+  // failed because there was a mistake in their command-line.
+  ensureWritable(Config->OptRemarksFilename, "optimization remarks file");
+  ensureWritable(Config->OutputFile, "output file");
+
   if (Args.hasArg(OPT_print_map))
     Config->MapFile = "-";
 
+  ensureWritable(Config->MapFile, "map file");
+
   // --omagic is an option to create old-fashioned executables in which
   // .text segments are writable. Today, the option is still in use to
   // create special-purpose programs such as boot loaders. It doesn't
Index: test/ELF/driver.test
===================================================================
--- test/ELF/driver.test
+++ test/ELF/driver.test
@@ -11,7 +11,7 @@
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 # RUN: not ld.lld %t -o /no/such/file 2>&1 | FileCheck -check-prefix=MISSING %s
-# MISSING: failed to open /no/such/file
+# MISSING: cannot write to output file /no/such/file
 
 # RUN: ld.lld --help 2>&1 | FileCheck -check-prefix=HELP %s
 # HELP: USAGE:
@@ -48,11 +48,11 @@
 
 ## "--output=foo" is equivalent to "-o foo".
 # RUN: not ld.lld %t --output=/no/such/file 2>&1 | FileCheck -check-prefix=ERR7 %s
-# ERR7: failed to open /no/such/file
+# ERR7: cannot write to output file /no/such/file
 
 ## "-output=foo" is equivalent to "-o utput=foo".
 # RUN: not ld.lld %t -output=/no/such/file 2>&1 | FileCheck -check-prefix=ERR8 %s
-# ERR8: failed to open utput=/no/such/file
+# ERR8: cannot write to output file utput=/no/such/file
 
 .globl _start
 _start:
Index: test/ELF/early-exit-for-bad-paths.s
===================================================================
--- test/ELF/early-exit-for-bad-paths.s
+++ test/ELF/early-exit-for-bad-paths.s
@@ -0,0 +1,56 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+
+# If the file was created by a previous test-run, we need to mark it as writable
+# or we will not be able to recreate its contents. However, chmod fails if the
+# file does not already exist, so we need to handle either case.
+# RUN: chmod 222 %t.readonly || true
+# RUN: echo This file is read only > %t.readonly
+# RUN: chmod 000 %t.readonly
+
+# RUN: not ld.lld %t.o -o does_not_exist/output 2>&1 | \
+# RUN:   FileCheck %s -check-prefixes=OUTPUT,NO-DIR,CHECK
+# RUN: not ld.lld %t.o -o %s/dir_is_a_file 2>&1 | \
+# RUN:   FileCheck %s -check-prefixes=OUTPUT,DIR-IS-FILE,CHECK
+# RUN: not ld.lld %t.o -o %p 2>&1 | \
+# RUN:   FileCheck %s -check-prefixes=OUTPUT,PATH-IS-DIR,CHECK
+# RUN: not ld.lld %t.o -o %t.readonly 2>&1 | \
+# RUN:   FileCheck %s -check-prefixes=OUTPUT,READ-ONLY,CHECK
+
+# RUN: not ld.lld %t.o -o %t.elf --Map=does_not_exist/output 2>&1 | \
+# RUN:   FileCheck %s -check-prefixes=MAP,NO-DIR,CHECK
+# RUN: not ld.lld %t.o -o %t.elf --Map=%s/dir_is_a_file 2>&1 | \
+# RUN:   FileCheck %s -check-prefixes=MAP,DIR-IS-FILE,CHECK
+# RUN: not ld.lld %t.o -o %t.elf --Map=%p 2>&1 | \
+# RUN:   FileCheck %s -check-prefixes=MAP,PATH-IS-DIR,CHECK
+# RUN: not ld.lld %t.o -o %t.elf --Map=%t.readonly 2>&1 | \
+# RUN:   FileCheck %s -check-prefixes=MAP,READ-ONLY,CHECK
+
+# RUN: not ld.lld %t.o -o %t.elf -opt-remarks-filename does_not_exist/output 2>&1 | \
+# RUN:   FileCheck %s -check-prefixes=OPTREMARKS,NO-DIR,CHECK
+# RUN: not ld.lld %t.o -o %t.elf -opt-remarks-filename %s/dir_is_a_file 2>&1 | \
+# RUN:   FileCheck %s -check-prefixes=OPTREMARKS,DIR-IS-FILE,CHECK
+# RUN: not ld.lld %t.o -o %t.elf -opt-remarks-filename %p 2>&1 | \
+# RUN:   FileCheck %s -check-prefixes=OPTREMARKS,PATH-IS-DIR,CHECK
+# RUN: not ld.lld %t.o -o %t.elf -opt-remarks-filename %t.readonly 2>&1 | \
+# RUN:   FileCheck %s -check-prefixes=OPTREMARKS,READ-ONLY,CHECK
+
+# OUTPUT: error: cannot write to output file
+# MAP: error: cannot write to map file
+# OPTREMARKS: error: cannot write to optimization remarks file
+
+# NO-DIR-SAME: does_not_exist/output:
+# DIR-IS-FILE-SAME: {{.*}}/dir_is_a_file:
+# PATH-IS-DIR-SAME: {{.*[\\/]}}ELF:
+# READ-ONLY-SAME: {{.*}}.readonly:
+
+# We should exit before doing the actual link. If an undefined symbol error is
+# discovered we haven't bailed out early as expected.
+# CHECK-NOT: undefined_symbol
+
+# RUN: FileCheck %s -check-prefix=UNCHANGED -input-file=%t.readonly
+# UNCHANGED: This file is read only
+
+  .globl _start
+_start:
+  call undefined_symbol
Index: test/ELF/map-file.s
===================================================================
--- test/ELF/map-file.s
+++ test/ELF/map-file.s
@@ -8,6 +8,10 @@
 // RUN: llvm-ar rc %t4.a %t4.o
 // RUN: ld.lld %t1.o %t2.o %t3.o %t4.a -o %t -M | FileCheck %s
 // RUN: ld.lld %t1.o %t2.o %t3.o %t4.a -o %t -print-map | FileCheck %s
+// RUN: ld.lld %t1.o %t2.o %t3.o %t4.a -o %t -Map=- | FileCheck %s
+// -Map=- is equivalent to -print-map. Verify that we do not create a
+// link map file "-" due to, for example, checking that "-" is writable.
+// RUN: not test -f -
 // RUN: ld.lld %t1.o %t2.o %t3.o %t4.a -o %t -Map=%t.map
 // RUN: FileCheck %s < %t.map
 
@@ -59,4 +63,4 @@
 
 // RUN: not ld.lld %t1.o %t2.o %t3.o %t4.a -o %t -Map=/ 2>&1 \
 // RUN:  | FileCheck -check-prefix=FAIL %s
-// FAIL: cannot open /
+// FAIL: cannot write to map file /