Index: llvm/trunk/tools/llvm-objcopy/CopyConfig.h
===================================================================
--- llvm/trunk/tools/llvm-objcopy/CopyConfig.h
+++ llvm/trunk/tools/llvm-objcopy/CopyConfig.h
@@ -115,6 +115,8 @@
 
   // Advanced options
   StringRef AddGnuDebugLink;
+  // Cached gnu_debuglink's target CRC
+  uint32_t GnuDebugLinkCRC32;
   StringRef BuildIdLinkDir;
   Optional<StringRef> BuildIdLinkInput;
   Optional<StringRef> BuildIdLinkOutput;
Index: llvm/trunk/tools/llvm-objcopy/CopyConfig.cpp
===================================================================
--- llvm/trunk/tools/llvm-objcopy/CopyConfig.cpp
+++ llvm/trunk/tools/llvm-objcopy/CopyConfig.cpp
@@ -16,6 +16,7 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compression.h"
 #include "llvm/Support/Errc.h"
+#include "llvm/Support/JamCRC.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/StringSaver.h"
 #include <memory>
@@ -490,6 +491,22 @@
   }
 
   Config.AddGnuDebugLink = InputArgs.getLastArgValue(OBJCOPY_add_gnu_debuglink);
+  // The gnu_debuglink's target is expected to not change or else its CRC would
+  // become invalidated and get rejected. We can avoid recalculating the
+  // checksum for every target file inside an archive by precomputing the CRC
+  // here. This prevents a significant amount of I/O.
+  if (!Config.AddGnuDebugLink.empty()) {
+    auto DebugOrErr = MemoryBuffer::getFile(Config.AddGnuDebugLink);
+    if (!DebugOrErr)
+      return createFileError(Config.AddGnuDebugLink, DebugOrErr.getError());
+    auto Debug = std::move(*DebugOrErr);
+    JamCRC CRC;
+    CRC.update(
+        ArrayRef<char>(Debug->getBuffer().data(), Debug->getBuffer().size()));
+    // The CRC32 value needs to be complemented because the JamCRC doesn't
+    // finalize the CRC32 value.
+    Config.GnuDebugLinkCRC32 = ~CRC.getCRC();
+  }
   Config.BuildIdLinkDir = InputArgs.getLastArgValue(OBJCOPY_build_id_link_dir);
   if (InputArgs.hasArg(OBJCOPY_build_id_link_input))
     Config.BuildIdLinkInput =
Index: llvm/trunk/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
===================================================================
--- llvm/trunk/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
+++ llvm/trunk/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
@@ -685,7 +685,8 @@
   }
 
   if (!Config.AddGnuDebugLink.empty())
-    Obj.addSection<GnuDebugLinkSection>(Config.AddGnuDebugLink);
+    Obj.addSection<GnuDebugLinkSection>(Config.AddGnuDebugLink,
+                                        Config.GnuDebugLinkCRC32);
 
   for (const NewSymbolInfo &SI : Config.SymbolsToAdd) {
     SectionBase *Sec = Obj.findSection(SI.SectionName);
Index: llvm/trunk/tools/llvm-objcopy/ELF/Object.h
===================================================================
--- llvm/trunk/tools/llvm-objcopy/ELF/Object.h
+++ llvm/trunk/tools/llvm-objcopy/ELF/Object.h
@@ -18,7 +18,6 @@
 #include "llvm/MC/StringTableBuilder.h"
 #include "llvm/Object/ELFObjectFile.h"
 #include "llvm/Support/FileOutputBuffer.h"
-#include "llvm/Support/JamCRC.h"
 #include <cstddef>
 #include <cstdint>
 #include <functional>
@@ -703,11 +702,11 @@
   StringRef FileName;
   uint32_t CRC32;
 
-  void init(StringRef File, StringRef Data);
+  void init(StringRef File);
 
 public:
   // If we add this section from an external source we can use this ctor.
-  explicit GnuDebugLinkSection(StringRef File);
+  explicit GnuDebugLinkSection(StringRef File, uint32_t PrecomputedCRC);
   void accept(SectionVisitor &Visitor) const override;
   void accept(MutableSectionVisitor &Visitor) override;
 };
Index: llvm/trunk/tools/llvm-objcopy/ELF/Object.cpp
===================================================================
--- llvm/trunk/tools/llvm-objcopy/ELF/Object.cpp
+++ llvm/trunk/tools/llvm-objcopy/ELF/Object.cpp
@@ -755,7 +755,7 @@
 
 void Section::finalize() { this->Link = LinkSection ? LinkSection->Index : 0; }
 
-void GnuDebugLinkSection::init(StringRef File, StringRef Data) {
+void GnuDebugLinkSection::init(StringRef File) {
   FileName = sys::path::filename(File);
   // The format for the .gnu_debuglink starts with the file name and is
   // followed by a null terminator and then the CRC32 of the file. The CRC32
@@ -770,21 +770,12 @@
   // establish the order that sections should go in. By using the maximum
   // possible offset we cause this section to wind up at the end.
   OriginalOffset = std::numeric_limits<uint64_t>::max();
-  JamCRC CRC;
-  CRC.update(ArrayRef<char>(Data.data(), Data.size()));
-  // The CRC32 value needs to be complemented because the JamCRC dosn't
-  // finalize the CRC32 value. It also dosn't negate the initial CRC32 value
-  // but it starts by default at 0xFFFFFFFF which is the complement of zero.
-  CRC32 = ~CRC.getCRC();
 }
 
-GnuDebugLinkSection::GnuDebugLinkSection(StringRef File) : FileName(File) {
-  // Read in the file to compute the CRC of it.
-  auto DebugOrErr = MemoryBuffer::getFile(File);
-  if (!DebugOrErr)
-    error("'" + File + "': " + DebugOrErr.getError().message());
-  auto Debug = std::move(*DebugOrErr);
-  init(File, Debug->getBuffer());
+GnuDebugLinkSection::GnuDebugLinkSection(StringRef File,
+                                         uint32_t PrecomputedCRC)
+    : FileName(File), CRC32(PrecomputedCRC) {
+  init(File);
 }
 
 template <class ELFT>