From bf8370ff36b504dfecd0594568f97c7a1a895c62 Mon Sep 17 00:00:00 2001
From: Bill Wendling <isanbard@gmail.com>
Date: Fri, 16 Jul 2010 22:51:10 +0000
Subject: Consider this function:

  void foo() { __builtin_unreachable(); }

It will output the following on Darwin X86:

_func1:
Leh_func_begin0:
        pushq %rbp
Ltmp0:
        movq %rsp, %rbp
Ltmp1:
Leh_func_end0:

This prolog adds a new Call Frame Information (CFI) row to the FDE with an
address that is not within the address range of the code it describes -- part is
equal to the end of the function -- and therefore results in an invalid EH
frame. If we emit a nop in this situation, then the CFI row is now within the
address range.

llvm-svn: 108568
---
 llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

(limited to 'llvm/lib')

diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 3d6dbb7a8f3..942b53a92dd 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -599,12 +599,15 @@ void AsmPrinter::EmitFunctionBody() {
   
   // Print out code for the function.
   bool HasAnyRealCode = false;
+  const MachineInstr *LastMI = 0;
   for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
        I != E; ++I) {
     // Print a label for the basic block.
     EmitBasicBlockStart(I);
     for (MachineBasicBlock::const_iterator II = I->begin(), IE = I->end();
          II != IE; ++II) {
+      LastMI = II;
+
       // Print the assembly for the instruction.
       if (!II->isLabel() && !II->isImplicitDef() && !II->isKill() &&
           !II->isDebugValue()) {
@@ -652,11 +655,18 @@ void AsmPrinter::EmitFunctionBody() {
       }
     }
   }
-  
+
+  // If the last instruction was a prolog label, then we have a situation where
+  // we emitted a prolog but no function body. This results in the ending prolog
+  // label equaling the end of function label and an invalid "row" in the
+  // FDE. We need to emit a noop in this situation so that the FDE's rows are
+  // valid.
+  bool RequiresNoop = LastMI && LastMI->getOpcode()==TargetOpcode::PROLOG_LABEL;
+
   // If the function is empty and the object file uses .subsections_via_symbols,
   // then we need to emit *something* to the function body to prevent the
   // labels from collapsing together.  Just emit a noop.
-  if (MAI->hasSubsectionsViaSymbols() && !HasAnyRealCode) {
+  if ((MAI->hasSubsectionsViaSymbols() && !HasAnyRealCode) || RequiresNoop) {
     MCInst Noop;
     TM.getInstrInfo()->getNoopForMachoTarget(Noop);
     if (Noop.getOpcode()) {
-- 
cgit v1.2.3