[PATCH] D43438: [dsymutil] Correctly handle DW_TAG_label

[Jonas Devlieghere via Phabricator via llvm-commits]

JDevlieghere created this revision.
JDevlieghere added reviewers: aprantl, davide.

This patch contains logic for handling DW_TAG_label that's present in darwin's dsymutil implementation, but not yet upstream.

It's missing a test case because I'm unable to generate a DW_TAG_label (https://llvm.org/PR36420). I'd like to get that fixed before checking this in, but I figured I'd already created the diff.


Repository:
  rL LLVM

https://reviews.llvm.org/D43438

Files:
  tools/dsymutil/DwarfLinker.cpp


Index: tools/dsymutil/DwarfLinker.cpp
===================================================================
--- tools/dsymutil/DwarfLinker.cpp
+++ tools/dsymutil/DwarfLinker.cpp
@@ -327,6 +327,7 @@
 
   uint64_t getLowPc() const { return LowPc; }
   uint64_t getHighPc() const { return HighPc; }
+  bool hasLabelAt(uint64_t Addr) const { return Labels.count(Addr); }
 
   Optional<PatchLocation> getUnitRangesAttribute() const {
     return UnitRangeAttribute;
@@ -366,6 +367,10 @@
   /// Apply all fixups recored by noteForwardReference().
   void fixupForwardReferences();
 
+  /// Add the low_pc of a label that is relocatad by applying
+  /// offset \p PCOffset.
+  void addLabelLowPc(uint64_t LabelLowPc, int64_t PcOffset);
+
   /// Add a function range [\p LowPC, \p HighPC) that is relocatad by applying
   /// offset \p PCOffset.
   void addFunctionRange(uint64_t LowPC, uint64_t HighPC, int64_t PCOffset);
@@ -471,6 +476,9 @@
   /// to the addresses to get the linked address.
   FunctionIntervals Ranges;
 
+  /// The DW_AT_low_pc of each DW_TAG_label.
+  SmallDenseMap<uint64_t, uint64_t, 1> Labels;
+
   /// DW_AT_ranges attributes to patch after we have gathered
   /// all the unit's function addresses.
   /// @{
@@ -585,6 +593,10 @@
   }
 }
 
+void CompileUnit::addLabelLowPc(uint64_t LabelLowPc, int64_t PcOffset) {
+  Labels.insert({LabelLowPc, PcOffset});
+}
+
 void CompileUnit::addFunctionRange(uint64_t FuncLowPc, uint64_t FuncHighPc,
                                    int64_t PcOffset) {
   Ranges.insert(FuncLowPc, FuncHighPc, PcOffset);
@@ -2458,7 +2470,7 @@
     return Flags;
 
   uint32_t Offset = DIE.getOffset() + getULEB128Size(Abbrev->getCode());
-  const DWARFUnit &OrigUnit = Unit.getOrigUnit();
+  DWARFUnit &OrigUnit = Unit.getOrigUnit();
   uint32_t LowPcOffset, LowPcEndOffset;
   std::tie(LowPcOffset, LowPcEndOffset) =
       getAttributeOffsets(Abbrev, *LowPcIdx, Offset, OrigUnit);
@@ -2476,6 +2488,21 @@
     DIE.dump(outs(), 8 /* Indent */, DumpOpts);
   }
 
+  if (DIE.getTag() == dwarf::DW_TAG_label) {
+    if (Unit.hasLabelAt(*LowPc))
+      return Flags;
+    // FIXME: dsymutil-classic compat. dsymutil-classic doesn't
+    // consider labels that don't fall into the CU's aranges. This is
+    // wrong IMO. Debug info generation bugs pu aside, this is really
+    // wrong in the case of labels, where a label marking the end of a
+    // function will have a PC == CU's high_pc.
+    if (dwarf::toAddress(OrigUnit.getUnitDIE().find(dwarf::DW_AT_high_pc))
+          .getValueOr(UINT64_MAX) <= LowPc)
+      return Flags;
+    Unit.addLabelLowPc(*LowPc, MyInfo.AddrAdjust);
+    return Flags | TF_Keep;
+  }
+
   Flags |= TF_Keep;
 
   Optional<uint64_t> HighPc = DIE.getHighPC(*LowPc);
@@ -2503,6 +2530,7 @@
   case dwarf::DW_TAG_variable:
     return shouldKeepVariableDIE(RelocMgr, DIE, Unit, MyInfo, Flags);
   case dwarf::DW_TAG_subprogram:
+  case dwarf::DW_TAG_label:
     return shouldKeepSubprogramDIE(RelocMgr, DIE, Unit, MyInfo, Flags);
   case dwarf::DW_TAG_imported_module:
   case dwarf::DW_TAG_imported_declaration:


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