Add legacy GNU entry value support to dsymutil

[aprantl]

Summary

Here is a blind attempt to make the legacy GNU attributes work in dsymutil — however it doesn't actually work yet. Since it's not perfectly clear to me how the GNU attributes map to the standardized version, help is appreciated!

[vsk]

Looks like all the DW_AT_low_pc handling is done earlier, on line 1045: if (AttrSpec.Attr == dwarf::DW_AT_low_pc) { ....

[aprantl]

Vedant convinced me that it is better to not attempt to support this. It's transitional anyway, and the LLDB tests have been skipped now.

llvm/lib/DWARFLinker/DWARFLinker.cpp

if (Die.getTag() == dwarf::DW_TAG_compile_unit) {
         Addr = HighPc;
       else
         return 0;
     } else
       // If we have a high_pc recorded for the input DIE, use
       // it. Otherwise (when no relocations where applied) just use the
       // one we just decoded.
       Addr = (Info.OrigHighPc ? Info.OrigHighPc : Addr) + Info.PCOffset;
-  } else if (AttrSpec.Attr == dwarf::DW_AT_call_return_pc) {
+  } else if ((AttrSpec.Attr == dwarf::DW_AT_call_return_pc &&
+              Die.getTag() == dwarf::DW_TAG_call_site) ||
+             (AttrSpec.Attr == dwarf::DW_AT_low_pc &&
+              Die.getTag() == dwarf::DW_TAG_GNU_call_site)) {
     // Relocate a return PC address within a call site entry.
-    if (Die.getTag() == dwarf::DW_TAG_call_site)
-      Addr = (Info.OrigCallReturnPc ? Info.OrigCallReturnPc : Addr) +
-             Info.PCOffset;
-  } else if (AttrSpec.Attr == dwarf::DW_AT_call_pc) {
+    Addr =
+        (Info.OrigCallReturnPc ? Info.OrigCallReturnPc : Addr) + Info.PCOffset;
+  } else if ((AttrSpec.Attr == dwarf::DW_AT_call_pc &&
+              Die.getTag() == dwarf::DW_TAG_call_site) ||
+             (AttrSpec.Attr == dwarf::DW_AT_low_pc &&
+              Die.getTag() == dwarf::DW_TAG_GNU_call_site)) {
     // Relocate the address of a branch instruction within a call site entry.
-    if (Die.getTag() == dwarf::DW_TAG_call_site)
-      Addr = (Info.OrigCallPc ? Info.OrigCallPc : Addr) + Info.PCOffset;
   }
 
   Die.addValue(DIEAlloc, static_cast<dwarf::Attribute>(AttrSpec.Attr),
                static_cast<dwarf::Form>(AttrSpec.Form), DIEInteger(Addr));
   return Unit.getOrigUnit().getAddressByteSize();
 }
 
 unsigned DWARFLinker::DIECloner::cloneScalarAttribute(
if (ObjFile.Addresses->areRelocationsResolved() &&
     // high_pc value is done in cloneAddressAttribute().
     AttrInfo.OrigHighPc =
         dwarf::toAddress(InputDIE.find(dwarf::DW_AT_high_pc), 0);
     // Also store the low_pc. It might get relocated in an
     // inline_subprogram that happens at the beginning of its
     // inlining function.
     AttrInfo.OrigLowPc = dwarf::toAddress(InputDIE.find(dwarf::DW_AT_low_pc),
                                           std::numeric_limits<uint64_t>::max());
-    AttrInfo.OrigCallReturnPc =
-        dwarf::toAddress(InputDIE.find(dwarf::DW_AT_call_return_pc), 0);
-    AttrInfo.OrigCallPc =
-        dwarf::toAddress(InputDIE.find(dwarf::DW_AT_call_pc), 0);
+    AttrInfo.OrigCallReturnPc = dwarf::toAddress(
+        InputDIE.find({dwarf::DW_AT_call_return_pc, dwarf::DW_AT_low_pc}), 0);
+    AttrInfo.OrigCallPc = dwarf::toAddress(
+        InputDIE.find({dwarf::DW_AT_call_pc, dwarf::DW_AT_low_pc}), 0);
   }
 
   // Reset the Offset to 0 as we will be working on the local copy of
   // the data.
   Offset = 0;
 
   const auto *Abbrev = InputDIE.getAbbreviationDeclarationPtr();
   Offset += getULEB128Size(Abbrev->getCode());