[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, 4 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 2f14f5464fd..5f91674d9f0 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -548,14 +548,15 @@ void DwarfDebug::constructCallSiteEntryDIEs(const DISubprogram &SP,
       // For tail calls, no return PC information is needed. For regular calls,
       // the return PC is needed to disambiguate paths in the call graph which
       // could lead to some target function.
-      const MCSymbol *ReturnPC = IsTail ? nullptr : getLabelAfterInsn(&MI);
+      const MCExpr *PCOffset =
+          IsTail ? nullptr : getFunctionLocalOffsetAfterInsn(&MI);
 
-      assert((IsTail || ReturnPC) && "Call without return PC information");
+      assert((IsTail || PCOffset) && "Call without return PC information");
       LLVM_DEBUG(dbgs() << "CallSiteEntry: " << MF.getName() << " -> "
                         << CalleeDecl->getName() << (IsTail ? " [tail]" : "")
                         << "\n");
       CU.constructCallSiteEntryDIE(ScopeDIE, *CalleeDecl->getSubprogram(),
-                                   IsTail, ReturnPC);
+                                   IsTail, PCOffset);
     }
   }
 }