Index: lib/Core/Reproduce.cpp
===================================================================
--- lib/Core/Reproduce.cpp
+++ lib/Core/Reproduce.cpp
@@ -53,7 +53,9 @@
 // Converts path to use unix path separators so the cpio can be extracted on
 // both unix and windows.
 static void convertToUnixPathSeparator(SmallString<128> &Path) {
+#ifdef LLVM_ON_WIN32
   std::replace(Path.begin(), Path.end(), '\\', '/');
+#endif
 }
 
 void CpioFile::append(StringRef Path, StringRef Data) {
Index: test/ELF/reproduce-backslash.s
===================================================================
--- /dev/null
+++ test/ELF/reproduce-backslash.s
@@ -0,0 +1,13 @@
+# REQUIRES: x86, cpio, shell
+
+# Test that we don't erroneously replace \ with / on UNIX, as it's
+# legal for a filename to contain backslashes.
+# RUN: rm -rf %t.dir
+# RUN: mkdir -p %t.dir/build
+# RUN: llvm-mc %s -o %t.dir/build/foo\\.o -filetype=obj -triple=x86_64-pc-linux
+# RUN: cd %t.dir
+# RUN: ld.lld build/foo\\.o --reproduce repro
+# RUN: cpio -t < repro.cpio | FileCheck %s
+
+# CHECK: repro/response.txt
+# CHECK: repro/{{.*}}/build/foo\.o