[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

1 files changed, 6 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
index 97a944e9b95..13679c37fe5 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
@@ -210,10 +210,10 @@ public:
 
   /// Construct a call site entry DIE describing a call within \p Scope to a
   /// callee described by \p CalleeSP. \p IsTail specifies whether the call is
-  /// a tail call. \p ReturnPC must be non-null for non-tail calls and point
-  /// to the PC value after the call returns.
+  /// a tail call. \p PCOffset must be non-zero for non-tail calls or be the
+  /// function-local offset to PC value after the call instruction.
   DIE &constructCallSiteEntryDIE(DIE &ScopeDIE, const DISubprogram &CalleeSP,
-                                 bool IsTail, const MCSymbol *ReturnPC);
+                                 bool IsTail, const MCExpr *PCOffset);
 
   /// Construct import_module DIE.
   DIE *constructImportedEntityDIE(const DIImportedEntity *Module);
@@ -292,6 +292,9 @@ public:
   /// Add a Dwarf expression attribute data and value.
   void addExpr(DIELoc &Die, dwarf::Form Form, const MCExpr *Expr);
 
+  /// Add an attribute containing an address expression to \p Die.
+  void addAddressExpr(DIE &Die, dwarf::Attribute Attribute, const MCExpr *Expr);
+
   void applySubprogramAttributesToDefinition(const DISubprogram *SP,
                                              DIE &SPDie);