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

This recommits 089c0f581492cd6e2a3d2927be3fbf60ea2d7e62, which was
reverted due to failing tests on big endian machines. It includes a fix
which I believe (I don't have BE machine) should fix this issue. The fix
consists of correcting the invocation DWARFYAML::EmitDebugSections,
which was missing one (default) function arguments, and so didn't
actually force the little-endian mode.

The original commit message follows.

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

1 files changed, 24 insertions, 0 deletions

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();