[PATCH] D78113: Fix DWARFDataExtractor::getRelocatedValue near EOF

[Pavel Labath via Phabricator via llvm-commits]

labath created this revision.
labath added reviewers: dblaikie, jhenderson.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.
labath added a child revision: D77556: [DWARFDataExtractor] Add a "truncating" constructor.

If we have an (invalid) relocation which relocates bytes which partially
lie outside the range of the relocated section, the getRelocatedValue
would return confusing results. It would first read zero (because that's
what the underlying DataExtractor api does for out-of-bounds reads, and
then relocate that zero anyway.

A more appropriate behavior is to return zero straight away. This is
what this patch does.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D78113

Files:
  llvm/lib/DebugInfo/DWARF/DWARFDataExtractor.cpp
  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
@@ -7,6 +7,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/DebugInfo/DWARF/DWARFDataExtractor.h"
+#include "llvm/DebugInfo/DWARF/DWARFContext.h"
+#include "llvm/Object/ObjectFile.h"
+#include "llvm/ObjectYAML/yaml2obj.h"
 #include "llvm/Testing/Support/Error.h"
 #include "gtest/gtest.h"
 
@@ -14,6 +17,54 @@
 
 namespace {
 
+TEST(DWARFDataExtractorTest, getRelocatedValue) {
+  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:  '000000000000'
+  - Name:     .rel.debug_line
+    Type:     SHT_REL
+    Info:     .debug_line
+    Relocations:
+      - Offset:   0
+        Symbol:   f
+        Type:     R_386_32
+      - 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(6u, DObj.getLineSection().Data.size());
+
+  DWARFDataExtractor Data(DObj, DObj.getLineSection(), Obj->isLittleEndian(),
+                          Obj->getBytesInAddress());
+  DataExtractor::Cursor C(0);
+  EXPECT_EQ(0x42u, Data.getRelocatedAddress(C));
+  EXPECT_EQ(0u, Data.getRelocatedAddress(C));
+  EXPECT_THAT_ERROR(C.takeError(),
+                    FailedWithMessage("unexpected end of data at offset 0x4"));
+}
+
 TEST(DWARFDataExtractorTest, getInitialLength) {
   auto GetWithError = [](ArrayRef<uint8_t> Bytes)
       -> Expected<std::tuple<uint64_t, dwarf::DwarfFormat, uint64_t>> {
Index: llvm/lib/DebugInfo/DWARF/DWARFDataExtractor.cpp
===================================================================
--- llvm/lib/DebugInfo/DWARF/DWARFDataExtractor.cpp
+++ llvm/lib/DebugInfo/DWARF/DWARFDataExtractor.cpp
@@ -50,9 +50,11 @@
     *SecNdx = object::SectionedAddress::UndefSection;
   if (!Section)
     return getUnsigned(Off, Size, Err);
+
+  ErrorAsOutParameter ErrAsOut(Err);
   Optional<RelocAddrEntry> E = Obj->find(*Section, *Off);
   uint64_t A = getUnsigned(Off, Size, Err);
-  if (!E)
+  if (!E || (Err && *Err))
     return A;
   if (SecNdx)
     *SecNdx = E->SectionIndex;


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