+/// When the 32-bit MSVC runtime transfers control to us, either to an outlined
+/// function or when returning to a parent frame after catching an exception, we
+/// recover the parent frame pointer by doing arithmetic on the incoming EBP.
+/// Here's the math:
+/// RegNodeBase = EntryEBP - RegNodeSize
+/// ParentFP = RegNodeBase - RegNodeFrameOffset
+/// Subtracting RegNodeSize takes us to the offset of the registration node, and
+/// subtracting the offset (negative on x86) takes us back to the parent FP.
+static SDValue recoverFramePointer(SelectionDAG &DAG, const Function *Fn,
+ SDValue EntryEBP) {
+ MachineFunction &MF = DAG.getMachineFunction();
+ SDLoc dl;
+
+ const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+ MVT PtrVT = TLI.getPointerTy();
+
+ // The RegNodeSize is 6 32-bit words for SEH and 4 for C++ EH. See
+ // WinEHStatePass for the full struct definition.
+ int RegNodeSize;
+ switch (classifyEHPersonality(Fn->getPersonalityFn())) {
+ default:
+ report_fatal_error("can only recover FP for MSVC EH personality functions");
+ case EHPersonality::MSVC_X86SEH: RegNodeSize = 24; break;
+ case EHPersonality::MSVC_CXX: RegNodeSize = 16; break;
+ }
+
+ // Get an MCSymbol that will ultimately resolve to the frame offset of the EH
+ // registration.
+ MCSymbol *OffsetSym =
+ MF.getMMI().getContext().getOrCreateParentFrameOffsetSymbol(
+ GlobalValue::getRealLinkageName(Fn->getName()));
+ SDValue OffsetSymVal = DAG.getMCSymbol(OffsetSym, PtrVT);
+ SDValue RegNodeFrameOffset =
+ DAG.getNode(ISD::FRAME_ALLOC_RECOVER, dl, PtrVT, OffsetSymVal);
+
+ // RegNodeBase = EntryEBP - RegNodeSize
+ // ParentFP = RegNodeBase - RegNodeFrameOffset
+ SDValue RegNodeBase = DAG.getNode(ISD::SUB, dl, PtrVT, EntryEBP,
+ DAG.getConstant(RegNodeSize, dl, PtrVT));
+ return DAG.getNode(ISD::SUB, dl, PtrVT, RegNodeBase, RegNodeFrameOffset);
+}
+