[PATCH] D86528: [4/5] [MC] [Win64EH] Fill in FuncletOrFuncEnd if missing

[Martin Storsjö via Phabricator via llvm-commits]

mstorsjo updated this revision to Diff 287867.
mstorsjo added a comment.

Wrote a bit longer comment explaining the issue with potentially truncated function length on `.seh_handlerdata`, left out the redundant place for filling in `FuncletOrFuncEnd`, and kept the fixme comment.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D86528/new/

https://reviews.llvm.org/D86528

Files:
  llvm/lib/MC/MCStreamer.cpp
  llvm/lib/MC/MCWin64EH.cpp
  llvm/test/MC/AArch64/seh.s


Index: llvm/test/MC/AArch64/seh.s
===================================================================
--- llvm/test/MC/AArch64/seh.s
+++ llvm/test/MC/AArch64/seh.s
@@ -49,6 +49,17 @@
 // CHECK-NEXT:   }
 // CHECK-NEXT: ]
 
+// CHECK-NEXT: UnwindInformation [
+// CHECK-NEXT:   RuntimeFunction {
+// CHECK-NEXT:     Function: func
+// CHECK-NEXT:     ExceptionRecord: .xdata
+// CHECK-NEXT:     ExceptionData {
+// CHECK-NEXT:       FunctionLength: 8
+// CHECK:        RuntimeFunction {
+// CHECK-NEXT:     Function: handlerFunc
+// CHECK-NEXT:     ExceptionRecord: .xdata
+// CHECK-NEXT:     ExceptionData {
+// CHECK-NEXT:       FunctionLength: 4
 
     .text
     .globl func
Index: llvm/lib/MC/MCWin64EH.cpp
===================================================================
--- llvm/lib/MC/MCWin64EH.cpp
+++ llvm/lib/MC/MCWin64EH.cpp
@@ -505,7 +505,12 @@
   int64_t RawFuncLength;
   if (!info->FuncletOrFuncEnd) {
     // FIXME: This is very wrong; we emit SEH data which covers zero bytes
-    // of code. But otherwise test/MC/AArch64/seh.s crashes.
+    // of code.
+    // This can happen if unwind info is forced to be generated at a point
+    // where the end of the function hasn't been determined yet, and where
+    // the current section at the time of generating the unwind info wasn't
+    // the text section, so we weren't able to automatically add a
+    // FuncletOrFuncEnd label.
     RawFuncLength = 0;
   } else {
     // FIXME: GetAbsDifference tries to compute the length of the function
@@ -687,6 +692,15 @@
 
 void llvm::Win64EH::ARM64UnwindEmitter::EmitUnwindInfo(
     MCStreamer &Streamer, WinEH::FrameInfo *info) const {
+  // Called if there's an .seh_handlerdata directive before the end of the
+  // function. This forces writing the xdata record already here - and
+  // in this case, the function isn't actually ended already, but the xdata
+  // record needs to know the function length. In these cases, if the funclet
+  // end hasn't been marked yet, the xdata function length won't cover the
+  // whole function, only up to this point.
+  if (!info->FuncletOrFuncEnd &&
+      Streamer.getCurrentSectionOnly() == info->TextSection)
+    info->FuncletOrFuncEnd = Streamer.emitCFILabel();
   // Switch sections (the static function above is meant to be called from
   // here and from Emit().
   MCSection *XData = Streamer.getAssociatedXDataSection(info->TextSection);
Index: llvm/lib/MC/MCStreamer.cpp
===================================================================
--- llvm/lib/MC/MCStreamer.cpp
+++ llvm/lib/MC/MCStreamer.cpp
@@ -692,6 +692,8 @@
 
   MCSymbol *Label = emitCFILabel();
   CurFrame->End = Label;
+  if (!CurFrame->FuncletOrFuncEnd)
+    CurFrame->FuncletOrFuncEnd = CurFrame->End;
 }
 
 void MCStreamer::EmitWinCFIFuncletOrFuncEnd(SMLoc Loc) {


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