Introduce a flag in SourceManager to treat non-system source files

as "volatile", meaning there's a high enough chance that they may
change while we are trying to use them.

This flag is only enabled by libclang.
Currently "volatile" source files will be stat'ed immediately
before opening them, because the file size stat info
may not be accurate since when we got it (e.g. from the PCH).
This avoids crashes when trying to reference mmap'ed memory
from a file whose size is not what we expect.

Note that there's still a window for a racing issue to occur
but the window for it should be way smaller than before.
We can consider later on to avoid mmap completely on such files.

rdar://11612916

llvm-svn: 160074

1 files changed, 11 insertions, 3 deletions

diff --git a/clang/lib/Basic/SourceManager.cpp b/clang/lib/Basic/SourceManager.cpp
index 5dc100a..9ec2474 100644
--- a/clang/lib/Basic/SourceManager.cpp
+++ b/clang/lib/Basic/SourceManager.cpp
@@ -97,7 +97,10 @@ const llvm::MemoryBuffer *ContentCache::getBuffer(DiagnosticsEngine &Diag,
   }    
 
   std::string ErrorStr;
-  Buffer.setPointer(SM.getFileManager().getBufferForFile(ContentsEntry, &ErrorStr));
+  bool isVolatile = SM.userFilesAreVolatile() && !IsSystemFile;
+  Buffer.setPointer(SM.getFileManager().getBufferForFile(ContentsEntry,
+                                                         &ErrorStr,
+                                                         isVolatile));
 
   // If we were unable to open the file, then we are in an inconsistent
   // situation where the content cache referenced a file which no longer
@@ -367,8 +370,10 @@ LineTableInfo &SourceManager::getLineTable() {
 // Private 'Create' methods.
 //===----------------------------------------------------------------------===//
 
-SourceManager::SourceManager(DiagnosticsEngine &Diag, FileManager &FileMgr)
+SourceManager::SourceManager(DiagnosticsEngine &Diag, FileManager &FileMgr,
+                             bool UserFilesAreVolatile)
   : Diag(Diag), FileMgr(FileMgr), OverridenFilesKeepOriginalName(true),
+    UserFilesAreVolatile(UserFilesAreVolatile),
     ExternalSLocEntries(0), LineTable(0), NumLinearScans(0),
     NumBinaryProbes(0), FakeBufferForRecovery(0),
     FakeContentCacheForRecovery(0) {
@@ -426,7 +431,8 @@ void SourceManager::clearIDTables() {
 /// getOrCreateContentCache - Create or return a cached ContentCache for the
 /// specified file.
 const ContentCache *
-SourceManager::getOrCreateContentCache(const FileEntry *FileEnt) {
+SourceManager::getOrCreateContentCache(const FileEntry *FileEnt,
+                                       bool isSystemFile) {
   assert(FileEnt && "Didn't specify a file entry to use?");
 
   // Do we already have information about this file?
@@ -455,6 +461,8 @@ SourceManager::getOrCreateContentCache(const FileEntry *FileEnt) {
     new (Entry) ContentCache(FileEnt);
   }
 
+  Entry->IsSystemFile = isSystemFile;
+
   return Entry;
 }