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
27using namespace llvm;
28using namespace llvm::lto;
29
30Expected<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}
151