1 files changed, 39 insertions, 11 deletions

diff --git a/tools/llvm-objcopy/Buffer.cpp b/tools/llvm-objcopy/Buffer.cpp
index 8044b023aaad..06b2a20a762f 100644
--- a/tools/llvm-objcopy/Buffer.cpp
+++ b/tools/llvm-objcopy/Buffer.cpp
@@ -1,16 +1,16 @@
 //===- Buffer.cpp ---------------------------------------------------------===//
 //
-//                      The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "Buffer.h"
-#include "llvm-objcopy.h"
 #include "llvm/Support/FileOutputBuffer.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Process.h"
 #include <memory>
 
 namespace llvm {
@@ -18,23 +18,51 @@ namespace objcopy {
 
 Buffer::~Buffer() {}
 
-void FileBuffer::allocate(size_t Size) {
+static Error createEmptyFile(StringRef FileName) {
+  // Create an empty tempfile and atomically swap it in place with the desired
+  // output file.
+  Expected<sys::fs::TempFile> Temp =
+      sys::fs::TempFile::create(FileName + ".temp-empty-%%%%%%%");
+  return Temp ? Temp->keep(FileName) : Temp.takeError();
+}
+
+Error FileBuffer::allocate(size_t Size) {
+  // When a 0-sized file is requested, skip allocation but defer file
+  // creation/truncation until commit() to avoid side effects if something
+  // happens between allocate() and commit().
+  if (Size == 0) {
+    EmptyFile = true;
+    return Error::success();
+  }
+
   Expected<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
       FileOutputBuffer::create(getName(), Size, FileOutputBuffer::F_executable);
-  handleAllErrors(BufferOrErr.takeError(), [this](const ErrorInfoBase &E) {
-    error("failed to open " + getName() + ": " + E.message());
-  });
+  // FileOutputBuffer::create() returns an Error that is just a wrapper around
+  // std::error_code. Wrap it in FileError to include the actual filename.
+  if (!BufferOrErr)
+    return createFileError(getName(), BufferOrErr.takeError());
   Buf = std::move(*BufferOrErr);
+  return Error::success();
 }
 
-Error FileBuffer::commit() { return Buf->commit(); }
+Error FileBuffer::commit() {
+  if (EmptyFile)
+    return createEmptyFile(getName());
+
+  assert(Buf && "allocate() not called before commit()!");
+  Error Err = Buf->commit();
+  // FileOutputBuffer::commit() returns an Error that is just a wrapper around
+  // std::error_code. Wrap it in FileError to include the actual filename.
+  return Err ? createFileError(getName(), std::move(Err)) : std::move(Err);
+}
 
 uint8_t *FileBuffer::getBufferStart() {
   return reinterpret_cast<uint8_t *>(Buf->getBufferStart());
 }
 
-void MemBuffer::allocate(size_t Size) {
+Error MemBuffer::allocate(size_t Size) {
   Buf = WritableMemoryBuffer::getNewMemBuffer(Size, getName());
+  return Error::success();
 }
 
 Error MemBuffer::commit() { return Error::success(); }