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/FileSystem.h"
17 #include "llvm/Support/MemoryBuffer.h"
18 #include "llvm/Support/Path.h"
19 #include "llvm/Support/Process.h"
20 #include "llvm/Support/raw_ostream.h"
21
22 #if !defined(_MSC_VER) && !defined(__MINGW32__)
23 #include <unistd.h>
24 #else
25 #include <io.h>
26 #endif
27
28 using namespace llvm;
29 using namespace llvm::lto;
30
localCache(StringRef CacheDirectoryPath,AddBufferFn AddBuffer)31 Expected<NativeObjectCache> lto::localCache(StringRef CacheDirectoryPath,
32 AddBufferFn AddBuffer) {
33 if (std::error_code EC = sys::fs::create_directories(CacheDirectoryPath))
34 return errorCodeToError(EC);
35
36 return [=](unsigned Task, StringRef Key) -> AddStreamFn {
37 // This choice of file name allows the cache to be pruned (see pruneCache()
38 // in include/llvm/Support/CachePruning.h).
39 SmallString<64> EntryPath;
40 sys::path::append(EntryPath, CacheDirectoryPath, "llvmcache-" + Key);
41 // First, see if we have a cache hit.
42 SmallString<64> ResultPath;
43 Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForRead(
44 Twine(EntryPath), sys::fs::OF_UpdateAtime, &ResultPath);
45 std::error_code EC;
46 if (FDOrErr) {
47 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
48 MemoryBuffer::getOpenFile(*FDOrErr, EntryPath,
49 /*FileSize=*/-1,
50 /*RequiresNullTerminator=*/false);
51 sys::fs::closeFile(*FDOrErr);
52 if (MBOrErr) {
53 AddBuffer(Task, std::move(*MBOrErr));
54 return AddStreamFn();
55 }
56 EC = MBOrErr.getError();
57 } else {
58 EC = errorToErrorCode(FDOrErr.takeError());
59 }
60
61 // On Windows we can fail to open a cache file with a permission denied
62 // error. This generally means that another process has requested to delete
63 // the file while it is still open, but it could also mean that another
64 // process has opened the file without the sharing permissions we need.
65 // Since the file is probably being deleted we handle it in the same way as
66 // if the file did not exist at all.
67 if (EC != errc::no_such_file_or_directory && EC != errc::permission_denied)
68 report_fatal_error(Twine("Failed to open cache file ") + EntryPath +
69 ": " + EC.message() + "\n");
70
71 // This native object stream is responsible for commiting the resulting
72 // file to the cache and calling AddBuffer to add it to the link.
73 struct CacheStream : NativeObjectStream {
74 AddBufferFn AddBuffer;
75 sys::fs::TempFile TempFile;
76 std::string EntryPath;
77 unsigned Task;
78
79 CacheStream(std::unique_ptr<raw_pwrite_stream> OS, AddBufferFn AddBuffer,
80 sys::fs::TempFile TempFile, std::string EntryPath,
81 unsigned Task)
82 : NativeObjectStream(std::move(OS)), AddBuffer(std::move(AddBuffer)),
83 TempFile(std::move(TempFile)), EntryPath(std::move(EntryPath)),
84 Task(Task) {}
85
86 ~CacheStream() {
87 // Make sure the stream is closed before committing it.
88 OS.reset();
89
90 // Open the file first to avoid racing with a cache pruner.
91 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
92 MemoryBuffer::getOpenFile(
93 sys::fs::convertFDToNativeFile(TempFile.FD), TempFile.TmpName,
94 /*FileSize=*/-1, /*RequiresNullTerminator=*/false);
95 if (!MBOrErr)
96 report_fatal_error(Twine("Failed to open new cache file ") +
97 TempFile.TmpName + ": " +
98 MBOrErr.getError().message() + "\n");
99
100 // On POSIX systems, this will atomically replace the destination if
101 // it already exists. We try to emulate this on Windows, but this may
102 // fail with a permission denied error (for example, if the destination
103 // is currently opened by another process that does not give us the
104 // sharing permissions we need). Since the existing file should be
105 // semantically equivalent to the one we are trying to write, we give
106 // AddBuffer a copy of the bytes we wrote in that case. We do this
107 // instead of just using the existing file, because the pruner might
108 // delete the file before we get a chance to use it.
109 Error E = TempFile.keep(EntryPath);
110 E = handleErrors(std::move(E), [&](const ECError &E) -> Error {
111 std::error_code EC = E.convertToErrorCode();
112 if (EC != errc::permission_denied)
113 return errorCodeToError(EC);
114
115 auto MBCopy = MemoryBuffer::getMemBufferCopy((*MBOrErr)->getBuffer(),
116 EntryPath);
117 MBOrErr = std::move(MBCopy);
118
119 // FIXME: should we consume the discard error?
120 consumeError(TempFile.discard());
121
122 return Error::success();
123 });
124
125 if (E)
126 report_fatal_error(Twine("Failed to rename temporary file ") +
127 TempFile.TmpName + " to " + EntryPath + ": " +
128 toString(std::move(E)) + "\n");
129
130 AddBuffer(Task, std::move(*MBOrErr));
131 }
132 };
133
134 return [=](size_t Task) -> std::unique_ptr<NativeObjectStream> {
135 // Write to a temporary to avoid race condition
136 SmallString<64> TempFilenameModel;
137 sys::path::append(TempFilenameModel, CacheDirectoryPath, "Thin-%%%%%%.tmp.o");
138 Expected<sys::fs::TempFile> Temp = sys::fs::TempFile::create(
139 TempFilenameModel, sys::fs::owner_read | sys::fs::owner_write);
140 if (!Temp) {
141 errs() << "Error: " << toString(Temp.takeError()) << "\n";
142 report_fatal_error("ThinLTO: Can't get a temporary file");
143 }
144
145 // This CacheStream will move the temporary file into the cache when done.
146 return std::make_unique<CacheStream>(
147 std::make_unique<raw_fd_ostream>(Temp->FD, /* ShouldClose */ false),
148 AddBuffer, std::move(*Temp), std::string(EntryPath.str()), Task);
149 };
150 };
151 }
152