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

[Martin Storsjö via Phabricator via llvm-commits]

mstorsjo created this revision.
mstorsjo added reviewers: efriedma, ssijaric, TomTan.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.
mstorsjo requested review of this revision.

This can happen e.g. for code that declare .seh_proc/.seh_endproc in assembly, or for code that use .seh_handlerdata (which triggers the unwind info to be emitted before the end of the function).

This should reduce the risk for unwind info entries with a zero function length.


Repository:
  rG LLVM Github Monorepo

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
@@ -48,6 +48,17 @@
 // 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: smallFunc
+// 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
@@ -504,8 +504,11 @@
 
   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.
+    // 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
@@ -663,6 +666,9 @@
 void llvm::Win64EH::ARM64UnwindEmitter::Emit(MCStreamer &Streamer) const {
   // Emit the unwind info structs first.
   for (const auto &CFI : Streamer.getWinFrameInfos()) {
+    if (!CFI->FuncletOrFuncEnd &&
+        Streamer.getCurrentSectionOnly() == CFI->TextSection)
+      CFI->FuncletOrFuncEnd = Streamer.emitCFILabel();
     MCSection *XData = Streamer.getAssociatedXDataSection(CFI->TextSection);
     Streamer.SwitchSection(XData);
     ARM64EmitUnwindInfo(Streamer, CFI.get());
@@ -680,6 +686,9 @@
     MCStreamer &Streamer, WinEH::FrameInfo *info) const {
   // Switch sections (the static function above is meant to be called from
   // here and from Emit().
+  if (!info->FuncletOrFuncEnd &&
+      Streamer.getCurrentSectionOnly() == info->TextSection)
+    info->FuncletOrFuncEnd = Streamer.emitCFILabel();
   MCSection *XData = Streamer.getAssociatedXDataSection(info->TextSection);
   Streamer.SwitchSection(XData);
   ARM64EmitUnwindInfo(Streamer, info);
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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