[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

2 files changed, 118 insertions, 0 deletions

diff --git a/llvm/unittests/DebugInfo/DWARF/CMakeLists.txt b/llvm/unittests/DebugInfo/DWARF/CMakeLists.txt
index 2181e0543d0..4fb79b2a96e 100644
--- a/llvm/unittests/DebugInfo/DWARF/CMakeLists.txt
+++ b/llvm/unittests/DebugInfo/DWARF/CMakeLists.txt
@@ -13,6 +13,7 @@ add_llvm_unittest(DebugInfoDWARFTests
   DwarfUtils.cpp
   DWARFDebugInfoTest.cpp
   DWARFDebugLineTest.cpp
+  DWARFDieTest.cpp
   DWARFFormValueTest.cpp
   DWARFLocationExpressionTest.cpp
   )
diff --git a/llvm/unittests/DebugInfo/DWARF/DWARFDieTest.cpp b/llvm/unittests/DebugInfo/DWARF/DWARFDieTest.cpp
new file mode 100644
index 00000000000..05e8e05b927
--- /dev/null
+++ b/llvm/unittests/DebugInfo/DWARF/DWARFDieTest.cpp
@@ -0,0 +1,117 @@
+//===- llvm/unittest/DebugInfo/DWARFDieTest.cpp ---------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/BinaryFormat/Dwarf.h"
+#include "llvm/DebugInfo/DWARF/DWARFContext.h"
+#include "llvm/ObjectYAML/DWARFEmitter.h"
+#include "llvm/Testing/Support/Error.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+using namespace llvm::dwarf;
+using object::SectionedAddress;
+
+namespace {
+
+TEST(DWARFLocationTable, getLocations) {
+  const char *yamldata = R"(
+    debug_abbrev:
+      - Code:            0x00000001
+        Tag:             DW_TAG_compile_unit
+        Children:        DW_CHILDREN_no
+        Attributes:
+          - Attribute:       DW_AT_location
+            Form:            DW_FORM_sec_offset
+          - Attribute:       DW_AT_data_member_location
+            Form:            DW_FORM_exprloc
+          - Attribute:       DW_AT_vtable_elem_location
+            Form:            DW_FORM_sec_offset
+          - Attribute:       DW_AT_call_data_location
+            Form:            DW_FORM_sec_offset
+    debug_info:
+      - Length:
+          TotalLength:     0
+        Version:         5
+        UnitType:        DW_UT_compile
+        AbbrOffset:      0
+        AddrSize:        4
+        Entries:
+          - AbbrCode:        0x00000001
+            Values:
+              - Value:           12
+              - Value:           0x0000000000000001
+                BlockData:       [ 0x47 ]
+              - Value:           20
+              - Value:           25
+  )";
+  Expected<StringMap<std::unique_ptr<MemoryBuffer>>> Sections =
+      DWARFYAML::EmitDebugSections(StringRef(yamldata),
+                                   /*IsLittleEndian=*/true);
+  ASSERT_THAT_EXPECTED(Sections, Succeeded());
+  std::vector<uint8_t> Loclists{
+      // Header
+      0, 0, 0, 0, // Length
+      5, 0,       // Version
+      4,          // Address size
+      0,          // Segment selector size
+      0, 0, 0, 0, // Offset entry count
+      // First location list.
+      DW_LLE_start_length, // First entry
+      1, 0, 0, 0,          // Start offset
+      2,                   // Length
+      0,                   // Expression length
+      DW_LLE_end_of_list,
+      // Second location list.
+      DW_LLE_startx_length, // First entry
+      1,                    // Start index
+      2,                    // Length
+      0,                    // Expression length
+      DW_LLE_end_of_list,
+      // Third location list.
+      DW_LLE_start_length, // First entry
+      1, 0, 0, 0,          // Start offset
+      2,                   // Length
+      0,                   // Expression length
+                           // end_of_list intentionally missing
+  };
+  Loclists[0] = Loclists.size() - 4;
+  Sections->try_emplace(
+      "debug_loclists",
+      MemoryBuffer::getMemBuffer(toStringRef(Loclists), "debug_loclists",
+                                 /*RequiresNullTerminator=*/false));
+  std::unique_ptr<DWARFContext> Ctx = DWARFContext::create(*Sections, 8);
+  DWARFCompileUnit *CU = Ctx->getCompileUnitForOffset(0);
+  ASSERT_NE(nullptr, CU);
+  DWARFDie Die = CU->getUnitDIE();
+  ASSERT_TRUE(Die.isValid());
+
+  EXPECT_THAT_EXPECTED(Die.getLocations(DW_AT_location),
+                       HasValue(testing::ElementsAre(DWARFLocationExpression{
+                           DWARFAddressRange{1, 3}, {}})));
+
+  EXPECT_THAT_EXPECTED(
+      Die.getLocations(DW_AT_data_member_location),
+      HasValue(testing::ElementsAre(DWARFLocationExpression{None, {0x47}})));
+
+  EXPECT_THAT_EXPECTED(
+      Die.getLocations(DW_AT_vtable_elem_location),
+      Failed<ErrorInfoBase>(testing::Property(
+          &ErrorInfoBase::message,
+          "Unable to resolve indirect address 1 for: DW_LLE_startx_length")));
+
+  EXPECT_THAT_EXPECTED(Die.getLocations(DW_AT_call_data_location),
+                       Failed<ErrorInfoBase>(testing::Property(
+                           &ErrorInfoBase::message, "unexpected end of data")));
+
+  EXPECT_THAT_EXPECTED(
+      Die.getLocations(DW_AT_call_data_value),
+      Failed<ErrorInfoBase>(testing::Property(&ErrorInfoBase::message,
+                                              "No DW_AT_call_data_value")));
+}
+
+} // end anonymous namespace