lib/LTO/Caching.cpp

   1 //===-Caching.cpp - LLVM Link Time Optimizer Cache Handling ---------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements the Caching for ThinLTO.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/LTO/Caching.h"
  14 #include "llvm/ADT/StringExtras.h"
  15 #include "llvm/Support/Errc.h"
  16 #include "llvm/Support/MemoryBuffer.h"
  17 #include "llvm/Support/Path.h"
  18 #include "llvm/Support/Process.h"
  19 #include "llvm/Support/raw_ostream.h"
  20
  21 #if !defined(_MSC_VER) && !defined(__MINGW32__)
  22 #include <unistd.h>
  23 #else
  24 #include <io.h>
  25 #endif
  26
  27 using namespace llvm;
  28 using namespace llvm::lto;
  29
  30 Expected<NativeObjectCache> lto::localCache(StringRef CacheDirectoryPath,
  31                                             AddBufferFn AddBuffer) {
  32   if (std::error_code EC = sys::fs::create_directories(CacheDirectoryPath))
  33     return errorCodeToError(EC);
  34
  35   return [=](unsigned Task, StringRef Key) -> AddStreamFn {
  36     // This choice of file name allows the cache to be pruned (see pruneCache()
  37     // in include/llvm/Support/CachePruning.h).
  38     SmallString<64> EntryPath;
  39     sys::path::append(EntryPath, CacheDirectoryPath, "llvmcache-" + Key);
  40     // First, see if we have a cache hit.
  41     int FD;
  42     SmallString<64> ResultPath;
  43     std::error_code EC = sys::fs::openFileForRead(
  44         Twine(EntryPath), FD, sys::fs::OF_UpdateAtime, &ResultPath);
  45     if (!EC) {
  46       ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
  47           MemoryBuffer::getOpenFile(FD, EntryPath,
  48                                     /*FileSize*/ -1,
  49                                     /*RequiresNullTerminator*/ false);
  50       close(FD);
  51       if (MBOrErr) {
  52         AddBuffer(Task, std::move(*MBOrErr));
  53         return AddStreamFn();
  54       }
  55       EC = MBOrErr.getError();
  56     }
  57
  58     // On Windows we can fail to open a cache file with a permission denied
  59     // error. This generally means that another process has requested to delete
  60     // the file while it is still open, but it could also mean that another
  61     // process has opened the file without the sharing permissions we need.
  62     // Since the file is probably being deleted we handle it in the same way as
  63     // if the file did not exist at all.
  64     if (EC != errc::no_such_file_or_directory && EC != errc::permission_denied)
  65       report_fatal_error(Twine("Failed to open cache file ") + EntryPath +
  66                          ": " + EC.message() + "\n");
  67
  68     // This native object stream is responsible for commiting the resulting
  69     // file to the cache and calling AddBuffer to add it to the link.
  70     struct CacheStream : NativeObjectStream {
  71       AddBufferFn AddBuffer;
  72       sys::fs::TempFile TempFile;
  73       std::string EntryPath;
  74       unsigned Task;
  75
  76       CacheStream(std::unique_ptr<raw_pwrite_stream> OS, AddBufferFn AddBuffer,
  77                   sys::fs::TempFile TempFile, std::string EntryPath,
  78                   unsigned Task)
  79           : NativeObjectStream(std::move(OS)), AddBuffer(std::move(AddBuffer)),
  80             TempFile(std::move(TempFile)), EntryPath(std::move(EntryPath)),
  81             Task(Task) {}
  82
  83       ~CacheStream() {
  84         // Make sure the stream is closed before committing it.
  85         OS.reset();
  86
  87         // Open the file first to avoid racing with a cache pruner.
  88         ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
  89             MemoryBuffer::getOpenFile(TempFile.FD, TempFile.TmpName,
  90                                       /*FileSize*/ -1,
  91                                       /*RequiresNullTerminator*/ false);
  92         if (!MBOrErr)
  93           report_fatal_error(Twine("Failed to open new cache file ") +
  94                              TempFile.TmpName + ": " +
  95                              MBOrErr.getError().message() + "\n");
  96
  97         // On POSIX systems, this will atomically replace the destination if
  98         // it already exists. We try to emulate this on Windows, but this may
  99         // fail with a permission denied error (for example, if the destination
 100         // is currently opened by another process that does not give us the
 101         // sharing permissions we need). Since the existing file should be
 102         // semantically equivalent to the one we are trying to write, we give
 103         // AddBuffer a copy of the bytes we wrote in that case. We do this
 104         // instead of just using the existing file, because the pruner might
 105         // delete the file before we get a chance to use it.
 106         Error E = TempFile.keep(EntryPath);
 107         E = handleErrors(std::move(E), [&](const ECError &E) -> Error {
 108           std::error_code EC = E.convertToErrorCode();
 109           if (EC != errc::permission_denied)
 110             return errorCodeToError(EC);
 111
 112           auto MBCopy = MemoryBuffer::getMemBufferCopy((*MBOrErr)->getBuffer(),
 113                                                        EntryPath);
 114           MBOrErr = std::move(MBCopy);
 115
 116           // FIXME: should we consume the discard error?
 117           consumeError(TempFile.discard());
 118
 119           return Error::success();
 120         });
 121
 122         if (E)
 123           report_fatal_error(Twine("Failed to rename temporary file ") +
 124                              TempFile.TmpName + " to " + EntryPath + ": " +
 125                              toString(std::move(E)) + "\n");
 126
 127         AddBuffer(Task, std::move(*MBOrErr));
 128       }
 129     };
 130
 131     return [=](size_t Task) -> std::unique_ptr<NativeObjectStream> {
 132       // Write to a temporary to avoid race condition
 133       SmallString<64> TempFilenameModel;
 134       sys::path::append(TempFilenameModel, CacheDirectoryPath, "Thin-%%%%%%.tmp.o");
 135       Expected<sys::fs::TempFile> Temp = sys::fs::TempFile::create(
 136           TempFilenameModel, sys::fs::owner_read | sys::fs::owner_write);
 137       if (!Temp) {
 138         errs() << "Error: " << toString(Temp.takeError()) << "\n";
 139         report_fatal_error("ThinLTO: Can't get a temporary file");
 140       }
 141
 142       // This CacheStream will move the temporary file into the cache when done.
 143       return llvm::make_unique<CacheStream>(
 144           llvm::make_unique<raw_fd_ostream>(Temp->FD, /* ShouldClose */ false),
 145           AddBuffer, std::move(*Temp), EntryPath.str(), Task);
 146     };
 147   };
 148 }