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llvm-mirror/tools/llvm-objcopy/Buffer.cpp
Jian Cai f73c5e8b40 [llvm-objcopy] preserve file ownership when overwritten by root
As of binutils 2.36, GNU strip calls chown(2) for "sudo strip foo" and
"sudo strip foo -o foo", but no "sudo strip foo -o bar" or "sudo strip
foo -o ./foo". In other words, while "sudo strip foo -o bar" creates a
new file bar with root access, "sudo strip foo" will keep the owner and
group of foo unchanged. Currently llvm-objcopy and llvm-strip behave
differently, always changing the owner and gropu to root. The
discrepancy prevents Chrome OS from migrating to llvm-objcopy and
llvm-strip as they change file ownership and cause intended users/groups
to lose access when invoked by sudo with the following sequence
(recommended in man page of GNU strip).

1.<Link the executable as normal.>
1.<Copy "foo" to "foo.full">
1.<Run "strip --strip-debug foo">
1.<Run "objcopy --add-gnu-debuglink=foo.full foo">

This patch makes llvm-objcopy and llvm-strip follow GNU's behavior.

Link: crbug.com/1108880
2021-02-12 18:01:43 -08:00

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//===- Buffer.cpp ---------------------------------------------------------===//
//
// 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/Support/FileOutputBuffer.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Process.h"
#include <memory>
namespace llvm {
namespace objcopy {
Buffer::~Buffer() {}
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,
KeepOwnership
? FileOutputBuffer::F_executable |
FileOutputBuffer::F_keep_ownership
: FileOutputBuffer::F_executable,
UserID, GroupID);
// 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() {
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());
}
Error MemBuffer::allocate(size_t Size) {
Buf = WritableMemoryBuffer::getNewMemBuffer(Size, getName());
return Error::success();
}
Error MemBuffer::commit() { return Error::success(); }
uint8_t *MemBuffer::getBufferStart() {
return reinterpret_cast<uint8_t *>(Buf->getBufferStart());
}
std::unique_ptr<WritableMemoryBuffer> MemBuffer::releaseMemoryBuffer() {
return std::move(Buf);
}
} // end namespace objcopy
} // end namespace llvm