1 //===-Caching.cpp - LLVM Link Time Optimizer Cache Handling ---------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the Caching for ThinLTO.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/LTO/Caching.h"
15 #include "llvm/ADT/StringExtras.h"
16 #include "llvm/Support/Errc.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 int FD;
43 SmallString<64> ResultPath;
44 std::error_code EC = sys::fs::openFileForRead(
45 Twine(EntryPath), FD, sys::fs::OF_UpdateAtime, &ResultPath);
46 if (!EC) {
47 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
48 MemoryBuffer::getOpenFile(FD, EntryPath,
49 /*FileSize*/ -1,
50 /*RequiresNullTerminator*/ false);
51 close(FD);
52 if (MBOrErr) {
53 AddBuffer(Task, std::move(*MBOrErr));
54 return AddStreamFn();
55 }
56 EC = MBOrErr.getError();
57 }
58
59 // On Windows we can fail to open a cache file with a permission denied
60 // error. This generally means that another process has requested to delete
61 // the file while it is still open, but it could also mean that another
62 // process has opened the file without the sharing permissions we need.
63 // Since the file is probably being deleted we handle it in the same way as
64 // if the file did not exist at all.
65 if (EC != errc::no_such_file_or_directory && EC != errc::permission_denied)
66 report_fatal_error(Twine("Failed to open cache file ") + EntryPath +
67 ": " + EC.message() + "\n");
68
69 // This native object stream is responsible for commiting the resulting
70 // file to the cache and calling AddBuffer to add it to the link.
71 struct CacheStream : NativeObjectStream {
72 AddBufferFn AddBuffer;
73 sys::fs::TempFile TempFile;
74 std::string EntryPath;
75 unsigned Task;
76
77 CacheStream(std::unique_ptr<raw_pwrite_stream> OS, AddBufferFn AddBuffer,
78 sys::fs::TempFile TempFile, std::string EntryPath,
79 unsigned Task)
80 : NativeObjectStream(std::move(OS)), AddBuffer(std::move(AddBuffer)),
81 TempFile(std::move(TempFile)), EntryPath(std::move(EntryPath)),
82 Task(Task) {}
83
84 ~CacheStream() {
85 // Make sure the stream is closed before committing it.
86 OS.reset();
87
88 // Open the file first to avoid racing with a cache pruner.
89 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
90 MemoryBuffer::getOpenFile(TempFile.FD, TempFile.TmpName,
91 /*FileSize*/ -1,
92 /*RequiresNullTerminator*/ false);
93 if (!MBOrErr)
94 report_fatal_error(Twine("Failed to open new cache file ") +
95 TempFile.TmpName + ": " +
96 MBOrErr.getError().message() + "\n");
97
98 // On POSIX systems, this will atomically replace the destination if
99 // it already exists. We try to emulate this on Windows, but this may
100 // fail with a permission denied error (for example, if the destination
101 // is currently opened by another process that does not give us the
102 // sharing permissions we need). Since the existing file should be
103 // semantically equivalent to the one we are trying to write, we give
104 // AddBuffer a copy of the bytes we wrote in that case. We do this
105 // instead of just using the existing file, because the pruner might
106 // delete the file before we get a chance to use it.
107 Error E = TempFile.keep(EntryPath);
108 E = handleErrors(std::move(E), [&](const ECError &E) -> Error {
109 std::error_code EC = E.convertToErrorCode();
110 if (EC != errc::permission_denied)
111 return errorCodeToError(EC);
112
113 auto MBCopy = MemoryBuffer::getMemBufferCopy((*MBOrErr)->getBuffer(),
114 EntryPath);
115 MBOrErr = std::move(MBCopy);
116
117 // FIXME: should we consume the discard error?
118 consumeError(TempFile.discard());
119
120 return Error::success();
121 });
122
123 if (E)
124 report_fatal_error(Twine("Failed to rename temporary file ") +
125 TempFile.TmpName + " to " + EntryPath + ": " +
126 toString(std::move(E)) + "\n");
127
128 AddBuffer(Task, std::move(*MBOrErr));
129 }
130 };
131
132 return [=](size_t Task) -> std::unique_ptr<NativeObjectStream> {
133 // Write to a temporary to avoid race condition
134 SmallString<64> TempFilenameModel;
135 sys::path::append(TempFilenameModel, CacheDirectoryPath, "Thin-%%%%%%.tmp.o");
136 Expected<sys::fs::TempFile> Temp = sys::fs::TempFile::create(
137 TempFilenameModel, sys::fs::owner_read | sys::fs::owner_write);
138 if (!Temp) {
139 errs() << "Error: " << toString(Temp.takeError()) << "\n";
140 report_fatal_error("ThinLTO: Can't get a temporary file");
141 }
142
143 // This CacheStream will move the temporary file into the cache when done.
144 return llvm::make_unique<CacheStream>(
145 llvm::make_unique<raw_fd_ostream>(Temp->FD, /* ShouldClose */ false),
146 AddBuffer, std::move(*Temp), EntryPath.str(), Task);
147 };
148 };
149 }
150