[codeview] Truncate records to maximum record size near 64KB

If we don't truncate, LLVM asserts when the label difference doesn't fit
in a 16 bit field. This patch truncates two kinds of data: trailing null
terminated names in symbol records, and inline line tables. The inline
line table test that I have is too large (many MB), so I'm not checking
it in.

Hopefully fixes PR28264.

llvm-svn: 283403

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

@@ -432,10 +432,13 @@ void CodeViewDebug::endModule() {
 }
 
 static void emitNullTerminatedSymbolName(MCStreamer &OS, StringRef S) {
-  // Microsoft's linker seems to have trouble with symbol names longer than
-  // 0xffd8 bytes.
-  S = S.substr(0, 0xffd8);
-  SmallString<32> NullTerminatedString(S);
+  // The maximum CV record length is 0xFF00. Most of the strings we emit appear
+  // after a fixed length portion of the record. The fixed length portion should
+  // always be less than 0xF00 (3840) bytes, so truncate the string so that the
+  // overall record size is less than the maximum allowed.
+  unsigned MaxFixedRecordLength = 0xF00;
+  SmallString<32> NullTerminatedString(
+      S.take_front(MaxRecordLength - MaxFixedRecordLength - 1));
   NullTerminatedString.push_back('\0');
   OS.EmitBytes(NullTerminatedString);
 }

llvm/lib/MC/MCCodeView.cpp

@@ -358,6 +358,13 @@ void CodeViewContext::encodeInlineLineTable(MCAsmLayout &Layout,
   SmallVectorImpl<char> &Buffer = Frag.getContents();
   Buffer.clear(); // Clear old contents if we went through relaxation.
   for (const MCCVLineEntry &Loc : Locs) {
+    // Exit early if our line table would produce an oversized InlineSiteSym
+    // record. Account for the ChangeCodeLength annotation emitted after the
+    // loop ends.
+    size_t MaxBufferSize = MaxRecordLength - sizeof(InlineSiteSym::Hdr) - 8;
+    if (Buffer.size() >= MaxBufferSize)
+      break;
+
     if (Loc.getFunctionId() == Frag.SiteFuncId) {
       CurSourceLoc.File = Loc.getFileNum();
       CurSourceLoc.Line = Loc.getLine();