[DWARF] Use a function-local offset for AT_call_return_pc
Logs provided by @stella.stamenova indicate that on Linux, lldb adds a
spurious slide offset to the return PC it loads from AT_call_return_pc
attributes (see the list thread: "[PATCH] D50478: Add support for
artificial tail call frames").
This patch side-steps the issue by getting rid of the load address
calculation in lldb's CallEdge::GetReturnPCAddress.
The idea is to have the DWARF writer emit function-local offsets to the
instruction after a call. I.e. return-pc = label-after-call-insn -
function-entry. LLDB can simply add this offset to the base address of a
function to get the return PC.
Differential Revision: https://reviews.llvm.org/D53469
llvm-svn: 344960
diff --git a/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp b/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
index 580f682..a362dd4 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
@@ -125,6 +125,21 @@
return LabelsAfterInsn.lookup(MI);
}
+// Return the function-local offset of an instruction.
+const MCExpr *
+DebugHandlerBase::getFunctionLocalOffsetAfterInsn(const MachineInstr *MI) {
+ MCContext &MC = Asm->OutContext;
+
+ MCSymbol *Start = Asm->getFunctionBegin();
+ const auto *StartRef = MCSymbolRefExpr::create(Start, MC);
+
+ MCSymbol *AfterInsn = getLabelAfterInsn(MI);
+ assert(AfterInsn && "Expected label after instruction");
+ const auto *AfterRef = MCSymbolRefExpr::create(AfterInsn, MC);
+
+ return MCBinaryExpr::createSub(AfterRef, StartRef, MC);
+}
+
/// If this type is derived from a base type then return base type size.
uint64_t DebugHandlerBase::getBaseTypeSize(const DITypeRef TyRef) {
DIType *Ty = TyRef.resolve();