PR42301: Abort cleanly if we encounter a huge source file rather than

crashing.

Ideally we wouldn't care about the size of a file so long as it fits in
memory, but in practice we have lots of hardocded assumptions that
unsigned can be used to index files, string literals, and so on.

llvm-svn: 364103

Author: zygoloid

clang/include/clang/Basic/DiagnosticCommonKinds.td

@@ -268,6 +268,8 @@ def err_opt_not_valid_on_target : Error<
 def err_cannot_open_file : Error<"cannot open file '%0': %1">, DefaultFatal;
 def err_file_modified : Error<
   "file '%0' modified since it was first processed">, DefaultFatal;
+def err_file_too_large : Error<
+  "sorry, unsupported: file '%0' is too large for Clang to process">;
 def err_unsupported_bom : Error<"%0 byte order mark detected in '%1', but "
   "encoding is not supported">, DefaultFatal;
 def err_unable_to_rename_temp : Error<

clang/lib/Basic/SourceManager.cpp

@@ -108,6 +108,31 @@ const llvm::MemoryBuffer *ContentCache::getBuffer(DiagnosticsEngine &Diag,
     return Buffer.getPointer();
   }
 
+  // Check that the file's size fits in an 'unsigned' (with room for a
+  // past-the-end value). This is deeply regrettable, but various parts of
+  // Clang (including elsewhere in this file!) use 'unsigned' to represent file
+  // offsets, line numbers, string literal lengths, and so on, and fail
+  // miserably on large source files.
+  if (ContentsEntry->getSize() >= std::numeric_limits<unsigned>::max()) {
+    // We can't make a memory buffer of the required size, so just make a small
+    // one. We should never hit a situation where we've already parsed to a
+    // later offset of the file, so it shouldn't matter that the buffer is
+    // smaller than the file.
+    Buffer.setPointer(
+        llvm::MemoryBuffer::getMemBuffer("", ContentsEntry->getName())
+            .release());
+    if (Diag.isDiagnosticInFlight())
+      Diag.SetDelayedDiagnostic(diag::err_file_too_large,
+                                ContentsEntry->getName());
+    else
+      Diag.Report(Loc, diag::err_file_too_large)
+        << ContentsEntry->getName();
+
+    Buffer.setInt(Buffer.getInt() | InvalidFlag);
+    if (Invalid) *Invalid = true;
+    return Buffer.getPointer();
+  }
+
   bool isVolatile = SM.userFilesAreVolatile() && !IsSystemFile;
   auto BufferOrError =
       SM.getFileManager().getBufferForFile(ContentsEntry, isVolatile);