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     SmallString<64> ResultPath;
  42     Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForRead(
  43         Twine(EntryPath), sys::fs::OF_UpdateAtime, &ResultPath);
  44     std::error_code EC;
  45     if (FDOrErr) {
  46       ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
  47           MemoryBuffer::getOpenFile(*FDOrErr, EntryPath,
  48                                     /*FileSize=*/-1,
  49                                     /*RequiresNullTerminator=*/false);
  50       sys::fs::closeFile(*FDOrErr);
  51       if (MBOrErr) {
  52         AddBuffer(Task, std::move(*MBOrErr));
  53         return AddStreamFn();
  54       }
  55       EC = MBOrErr.getError();
  56     } else {
  57       EC = errorToErrorCode(FDOrErr.takeError());
  58     }
  59
  60     // On Windows we can fail to open a cache file with a permission denied
  61     // error. This generally means that another process has requested to delete
  62     // the file while it is still open, but it could also mean that another
  63     // process has opened the file without the sharing permissions we need.
  64     // Since the file is probably being deleted we handle it in the same way as
  65     // if the file did not exist at all.
  66     if (EC != errc::no_such_file_or_directory && EC != errc::permission_denied)
  67       report_fatal_error(Twine("Failed to open cache file ") + EntryPath +
  68                          ": " + EC.message() + "\n");
  69
  70     // This native object stream is responsible for commiting the resulting
  71     // file to the cache and calling AddBuffer to add it to the link.
  72     struct CacheStream : NativeObjectStream {
  73       AddBufferFn AddBuffer;
  74       sys::fs::TempFile TempFile;
  75       std::string EntryPath;
  76       unsigned Task;
  77
  78       CacheStream(std::unique_ptr<raw_pwrite_stream> OS, AddBufferFn AddBuffer,
  79                   sys::fs::TempFile TempFile, std::string EntryPath,
  80                   unsigned Task)
  81           : NativeObjectStream(std::move(OS)), AddBuffer(std::move(AddBuffer)),
  82             TempFile(std::move(TempFile)), EntryPath(std::move(EntryPath)),
  83             Task(Task) {}
  84
  85       ~CacheStream() {
  86         // Make sure the stream is closed before committing it.
  87         OS.reset();
  88
  89         // Open the file first to avoid racing with a cache pruner.
  90         ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
  91             MemoryBuffer::getOpenFile(
  92                 sys::fs::convertFDToNativeFile(TempFile.FD), TempFile.TmpName,
  93                 /*FileSize=*/-1, /*RequiresNullTerminator=*/false);
  94         if (!MBOrErr)
  95           report_fatal_error(Twine("Failed to open new cache file ") +
  96                              TempFile.TmpName + ": " +
  97                              MBOrErr.getError().message() + "\n");
  98
  99         // On POSIX systems, this will atomically replace the destination if
 100         // it already exists. We try to emulate this on Windows, but this may
 101         // fail with a permission denied error (for example, if the destination
 102         // is currently opened by another process that does not give us the
 103         // sharing permissions we need). Since the existing file should be
 104         // semantically equivalent to the one we are trying to write, we give
 105         // AddBuffer a copy of the bytes we wrote in that case. We do this
 106         // instead of just using the existing file, because the pruner might
 107         // delete the file before we get a chance to use it.
 108         Error E = TempFile.keep(EntryPath);
 109         E = handleErrors(std::move(E), [&](const ECError &E) -> Error {
 110           std::error_code EC = E.convertToErrorCode();
 111           if (EC != errc::permission_denied)
 112             return errorCodeToError(EC);
 113
 114           auto MBCopy = MemoryBuffer::getMemBufferCopy((*MBOrErr)->getBuffer(),
 115                                                        EntryPath);
 116           MBOrErr = std::move(MBCopy);
 117
 118           // FIXME: should we consume the discard error?
 119           consumeError(TempFile.discard());
 120
 121           return Error::success();
 122         });
 123
 124         if (E)
 125           report_fatal_error(Twine("Failed to rename temporary file ") +
 126                              TempFile.TmpName + " to " + EntryPath + ": " +
 127                              toString(std::move(E)) + "\n");
 128
 129         AddBuffer(Task, std::move(*MBOrErr));
 130       }
 131     };
 132
 133     return [=](size_t Task) -> std::unique_ptr<NativeObjectStream> {
 134       // Write to a temporary to avoid race condition
 135       SmallString<64> TempFilenameModel;
 136       sys::path::append(TempFilenameModel, CacheDirectoryPath, "Thin-%%%%%%.tmp.o");
 137       Expected<sys::fs::TempFile> Temp = sys::fs::TempFile::create(
 138           TempFilenameModel, sys::fs::owner_read | sys::fs::owner_write);
 139       if (!Temp) {
 140         errs() << "Error: " << toString(Temp.takeError()) << "\n";
 141         report_fatal_error("ThinLTO: Can't get a temporary file");
 142       }
 143
 144       // This CacheStream will move the temporary file into the cache when done.
 145       return std::make_unique<CacheStream>(
 146           std::make_unique<raw_fd_ostream>(Temp->FD, /* ShouldClose */ false),
 147           AddBuffer, std::move(*Temp), EntryPath.str(), Task);
 148     };
 149   };
 150 }