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LTO: Create temporary cache files in the cache directory instead of $TMPDIR. 

This fixes a race condition where another linker process can observe a
partially written file if we copy it from another file system, and allows
the link to be independent of the amount of free disk space in $TMPDIR.

Differential Revision: https://reviews.llvm.org/D31045

llvm-svn: 297970
This commit is contained in:
Peter Collingbourne 2017-03-16 18:20:06 +00:00
parent dc855221af
commit cb46a6baf7
1 changed files with 8 additions and 28 deletions
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36
llvm/lib/LTO/Caching.cpp
View File

@ -21,31 +21,6 @@
using namespace llvm;
using namespace llvm::lto;
static void commitEntry(StringRef TempFilename, StringRef EntryPath) {
// Rename to final destination (hopefully race condition won't matter here)
auto EC = sys::fs::rename(TempFilename, EntryPath);
if (EC) {
// Renaming failed, probably not the same filesystem, copy and delete.
// FIXME: Avoid needing to do this by creating the temporary file in the
// cache directory.
{
auto ReloadedBufferOrErr = MemoryBuffer::getFile(TempFilename);
if (auto EC = ReloadedBufferOrErr.getError())
report_fatal_error(Twine("Failed to open temp file '") + TempFilename +
"': " + EC.message() + "\n");
raw_fd_ostream OS(EntryPath, EC, sys::fs::F_None);
if (EC)
report_fatal_error(Twine("Failed to open ") + EntryPath +
" to save cached entry\n");
// I'm not sure what are the guarantee if two processes are doing this
// at the same time.
OS << (*ReloadedBufferOrErr)->getBuffer();
}
sys::fs::remove(TempFilename);
}
}
Expected<NativeObjectCache> lto::localCache(StringRef CacheDirectoryPath,
AddFileFn AddFile) {
if (std::error_code EC = sys::fs::create_directories(CacheDirectoryPath))
@ -78,7 +53,10 @@ Expected<NativeObjectCache> lto::localCache(StringRef CacheDirectoryPath,
~CacheStream() {
// Make sure the file is closed before committing it.
OS.reset();
commitEntry(TempFilename, EntryPath);
// This is atomic on POSIX systems.
if (auto EC = sys::fs::rename(TempFilename, EntryPath))
report_fatal_error(Twine("Failed to rename temporary file ") +
TempFilename + ": " + EC.message() + "\n");
AddFile(Task, EntryPath);
}
};
@ -86,9 +64,11 @@ Expected<NativeObjectCache> lto::localCache(StringRef CacheDirectoryPath,
return [=](size_t Task) -> std::unique_ptr<NativeObjectStream> {
// Write to a temporary to avoid race condition
int TempFD;
SmallString<64> TempFilename;
SmallString<64> TempFilenameModel, TempFilename;
sys::path::append(TempFilenameModel, CacheDirectoryPath, "Thin-%%%%%%.tmp.o");
std::error_code EC =
sys::fs::createTemporaryFile("Thin", "tmp.o", TempFD, TempFilename);
sys::fs::createUniqueFile(TempFilenameModel, TempFD, TempFilename,
sys::fs::owner_read | sys::fs::owner_write);
if (EC) {
errs() << "Error: " << EC.message() << "\n";
report_fatal_error("ThinLTO: Can't get a temporary file");