[DWARF] Add an api to get "interpreted" location lists

Summary:
This patch adds DWARFDie::getLocations, which returns the location
expressions for a given attribute (typically DW_AT_location). It handles
both "inline" locations and references to the external location list
sections (currently only of the DW_FORM_sec_offset type). It is
implemented on top of DWARFUnit::findLoclistFromOffset, which is also
added in this patch. I tried to make their signatures similar to the
equivalent range list functionality.

The actual location list interpretation logic is in
DWARFLocationTable::visitAbsoluteLocationList. This part is not
equivalent to the range list code, but this deviation is motivated by a
desire to reuse the same location list parsing code within lldb.

The functionality is tested via a c++ unit test of the DWARFDie API.

Reviewers: dblaikie, JDevlieghere, SouraVX

Subscribers: mgorny, hiraditya, cmtice, probinson, llvm-commits, aprantl

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70394

3 files changed, 60 insertions, 0 deletions

diff --git a/llvm/lib/DebugInfo/DWARF/DWARFDebugLoc.cpp b/llvm/lib/DebugInfo/DWARF/DWARFDebugLoc.cpp
index 1af51a85d18..8b84822914d 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFDebugLoc.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFDebugLoc.cpp
@@ -151,6 +151,21 @@ bool DWARFLocationTable::dumpLocationList(uint64_t *Offset, raw_ostream &OS,
   return true;
 }
 
+Error DWARFLocationTable::visitAbsoluteLocationList(
+    uint64_t Offset, Optional<SectionedAddress> BaseAddr,
+    std::function<Optional<SectionedAddress>(uint32_t)> LookupAddr,
+    function_ref<bool(Expected<DWARFLocationExpression>)> Callback) const {
+  DWARFLocationInterpreter Interp(BaseAddr, std::move(LookupAddr));
+  return visitLocationList(&Offset, [&](const DWARFLocationEntry &E) {
+    Expected<Optional<DWARFLocationExpression>> Loc = Interp.Interpret(E);
+    if (!Loc)
+      return Callback(Loc.takeError());
+    if (*Loc)
+      return Callback(**Loc);
+    return true;
+  });
+}
+
 DWARFDebugLoc::LocationList const *
 DWARFDebugLoc::getLocationListAtOffset(uint64_t Offset) const {
   auto It = partition_point(
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp b/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
index a11865e048c..6cf30270539 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
@@ -486,6 +486,27 @@ bool DWARFDie::addressRangeContainsAddress(const uint64_t Address) const {
   return false;
 }
 
+Expected<DWARFLocationExpressionsVector>
+DWARFDie::getLocations(dwarf::Attribute Attr) const {
+  Optional<DWARFFormValue> Location = find(Attr);
+  if (!Location)
+    return createStringError(inconvertibleErrorCode(), "No %s",
+                             dwarf::AttributeString(Attr).data());
+
+  if (Optional<uint64_t> Off = Location->getAsSectionOffset())
+    return U->findLoclistFromOffset(*Off);
+
+  if (Optional<ArrayRef<uint8_t>> Expr = Location->getAsBlock()) {
+    return DWARFLocationExpressionsVector{
+        DWARFLocationExpression{None, to_vector<4>(*Expr)}};
+  }
+
+  return createStringError(
+      inconvertibleErrorCode(), "Unsupported %s encoding: %s",
+      dwarf::AttributeString(Attr).data(),
+      dwarf::FormEncodingString(Location->getForm()).data());
+}
+
 const char *DWARFDie::getSubroutineName(DINameKind Kind) const {
   if (!isSubroutineDIE())
     return nullptr;
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp b/llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp
index 2eb7d2f945a..e5d33e13644 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp
@@ -637,6 +637,30 @@ Expected<DWARFAddressRangesVector> DWARFUnit::collectAddressRanges() {
   return *CUDIERangesOrError;
 }
 
+Expected<DWARFLocationExpressionsVector>
+DWARFUnit::findLoclistFromOffset(uint64_t Offset) {
+  DWARFLocationExpressionsVector Result;
+
+  Error InterpretationError = Error::success();
+
+  Error ParseError = getLocationTable().visitAbsoluteLocationList(
+      Offset, getBaseAddress(),
+      [this](uint32_t Index) { return getAddrOffsetSectionItem(Index); },
+      [&](Expected<DWARFLocationExpression> L) {
+        if (L)
+          Result.push_back(std::move(*L));
+        else
+          InterpretationError =
+              joinErrors(L.takeError(), std::move(InterpretationError));
+        return !InterpretationError;
+      });
+
+  if (ParseError || InterpretationError)
+    return joinErrors(std::move(ParseError), std::move(InterpretationError));
+
+  return Result;
+}
+
 void DWARFUnit::updateAddressDieMap(DWARFDie Die) {
   if (Die.isSubroutineDIE()) {
     auto DIERangesOrError = Die.getAddressRanges();