[PATCH] D77556: [DWARFDataExtractor] Add a "truncating" constructor

[Pavel Labath via Phabricator via llvm-commits]

labath updated this revision to Diff 257352.
labath added a comment.

- add more tests for reads which cross extractor boundaries. This required a fix to getRelocatedValue, which was spun out to a separate patch
- this patch does not (yet) introduce any additional constructors


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D77556/new/

https://reviews.llvm.org/D77556

Files:
  llvm/include/llvm/DebugInfo/DWARF/DWARFDataExtractor.h
  llvm/unittests/DebugInfo/DWARF/DWARFDataExtractorTest.cpp


Index: llvm/unittests/DebugInfo/DWARF/DWARFDataExtractorTest.cpp
===================================================================
--- llvm/unittests/DebugInfo/DWARF/DWARFDataExtractorTest.cpp
+++ llvm/unittests/DebugInfo/DWARF/DWARFDataExtractorTest.cpp
@@ -146,4 +146,70 @@
             std::make_tuple(0x0001020304050607, dwarf::DWARF64, 12));
 }
 
+TEST(DWARFDataExtractorTest, Truncation) {
+  StringRef Yaml = R"(
+!ELF
+FileHeader:
+  Class:    ELFCLASS32
+  Data:     ELFDATA2LSB
+  Type:     ET_REL
+  Machine:  EM_386
+Sections:
+  - Name:     .text
+    Type:     SHT_PROGBITS
+    Size:     0x80
+  - Name:     .debug_line
+    Type:     SHT_PROGBITS
+    Content:  '616263640000000065666768'
+  - Name:     .rel.debug_line
+    Type:     SHT_REL
+    Info:     .debug_line
+    Relocations:
+      - Offset:   4
+        Symbol:   f
+        Type:     R_386_32
+Symbols:
+  - Name:     f
+    Type:     STT_SECTION
+    Section:  .text
+    Value:    0x42
+)";
+  SmallString<0> Storage;
+  std::unique_ptr<object::ObjectFile> Obj =
+      yaml::yaml2ObjectFile(Storage, Yaml, [](Twine Err) { errs() << Err; });
+  ASSERT_TRUE(Obj);
+  std::unique_ptr<DWARFContext> Ctx = DWARFContext::create(*Obj);
+  const DWARFObject &DObj = Ctx->getDWARFObj();
+  ASSERT_EQ(12u, DObj.getLineSection().Data.size());
+
+  DWARFDataExtractor Data(DObj, DObj.getLineSection(), Obj->isLittleEndian(),
+                          Obj->getBytesInAddress());
+  DataExtractor::Cursor C(0);
+  EXPECT_EQ(0x64636261u, Data.getRelocatedAddress(C));
+  EXPECT_EQ(0x42u, Data.getRelocatedAddress(C));
+  EXPECT_EQ(0x68676665u, Data.getRelocatedAddress(C));
+  EXPECT_THAT_ERROR(C.takeError(), Succeeded());
+
+  C = DataExtractor::Cursor{0};
+  DWARFDataExtractor Truncated8(Data, 8);
+  EXPECT_EQ(0x64636261u, Truncated8.getRelocatedAddress(C));
+  EXPECT_EQ(0x42u, Truncated8.getRelocatedAddress(C));
+  EXPECT_EQ(0x0u, Truncated8.getRelocatedAddress(C));
+  EXPECT_THAT_ERROR(C.takeError(),
+                    FailedWithMessage("unexpected end of data at offset 0x8"));
+
+  C = DataExtractor::Cursor{0};
+  DWARFDataExtractor Truncated6(Data, 6);
+  EXPECT_EQ(0x64636261u, Truncated6.getRelocatedAddress(C));
+  EXPECT_EQ(0x0u, Truncated6.getRelocatedAddress(C));
+  EXPECT_THAT_ERROR(C.takeError(),
+                    FailedWithMessage("unexpected end of data at offset 0x4"));
+
+  C = DataExtractor::Cursor{0};
+  DWARFDataExtractor Truncated2(Data, 2);
+  EXPECT_EQ(0x0u, Truncated2.getRelocatedAddress(C));
+  EXPECT_THAT_ERROR(C.takeError(),
+                    FailedWithMessage("unexpected end of data at offset 0x0"));
+}
+
 } // namespace
Index: llvm/include/llvm/DebugInfo/DWARF/DWARFDataExtractor.h
===================================================================
--- llvm/include/llvm/DebugInfo/DWARF/DWARFDataExtractor.h
+++ llvm/include/llvm/DebugInfo/DWARF/DWARFDataExtractor.h
@@ -39,6 +39,12 @@
             StringRef(reinterpret_cast<const char *>(Data.data()), Data.size()),
             IsLittleEndian, AddressSize) {}
 
+  /// Truncating constructor
+  DWARFDataExtractor(const DWARFDataExtractor &Other, size_t Length)
+      : DataExtractor(Other.getData().substr(0, Length), Other.isLittleEndian(),
+                      Other.getAddressSize()),
+        Obj(Other.Obj), Section(Other.Section) {}
+
   /// Extracts the DWARF "initial length" field, which can either be a 32-bit
   /// value smaller than 0xfffffff0, or the value 0xffffffff followed by a
   /// 64-bit length. Returns the actual length, and the DWARF format which is


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