[lldb][llvm] Return an error instead of crashing when parsing a line table prologue.

[clayborg]

We recently ran into some bad DWARF where the DW_AT_stmt_list of many compile units was randomly set to invalid values and was causing LLDB to crash due to an assertion about address sizes not matching. Instead of asserting, we should return an appropriate recoverable llvm::Error.

[llvmbot]

@llvm/pr-subscribers-debuginfo

Author: Greg Clayton (clayborg)

Changes

We recently ran into some bad DWARF where the DW_AT_stmt_list of many compile units was randomly set to invalid values and was causing LLDB to crash due to an assertion about address sizes not matching. Instead of asserting, we should return an appropriate llvm::Error. There was also a complication as the address size might be invalid or the cursor might have ran into the end of the .debug_line section. To handle this I added a new lambda that will return the correct error if the cursor is still in a valid state, or return the cursor error if the cursor has one.

---

Full diff: https://github.com/llvm/llvm-project/pull/80769.diff

2 Files Affected:

• (modified) llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp (+37-7)
• (modified) llvm/unittests/DebugInfo/DWARF/DWARFDebugLineTest.cpp (+4-9)

diff --git a/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp b/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
index 28f05644a3aa1..60513f09936aa 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
@@ -372,26 +372,56 @@ Error DWARFDebugLine::Prologue::parse(
   std::tie(TotalLength, FormParams.Format) =
       DebugLineData.getInitialLength(Cursor);
 
+  // Report an error, but also make sure the cursor is not in a bad state. If
+  // the cursor is in a bad state, return its error instead. Many times during
+  // parsing we might end up bailing if we don't like what we see, but often
+  // times when we decode items with a bad cursor, we will get zero back which
+  // might not be valid data to extract.
+  auto ReportErrorOrCursor = [&](llvm::Error Error) -> llvm::Error {
+    if (Cursor)
+      return Error;
+    llvm::consumeError(std::move(Error));
+    *OffsetPtr = Cursor.tell();
+    std::string CursorErrorStr = llvm::toString(Cursor.takeError());
+    return createStringError(
+        errc::not_supported,
+        "parsing line table prologue at offset 0x%8.8" PRIx64 ": %s",
+        PrologueOffset, CursorErrorStr.c_str());
+  };
+
   DebugLineData =
       DWARFDataExtractor(DebugLineData, Cursor.tell() + TotalLength);
   FormParams.Version = DebugLineData.getU16(Cursor);
-  if (Cursor && !versionIsSupported(getVersion())) {
+  if (!versionIsSupported(getVersion())) {
     // Treat this error as unrecoverable - we cannot be sure what any of
     // the data represents including the length field, so cannot skip it or make
     // any reasonable assumptions.
-    *OffsetPtr = Cursor.tell();
-    return createStringError(
+    return ReportErrorOrCursor(createStringError(
         errc::not_supported,
         "parsing line table prologue at offset 0x%8.8" PRIx64
         ": unsupported version %" PRIu16,
-        PrologueOffset, getVersion());
+        PrologueOffset, getVersion()));
   }
 
   if (getVersion() >= 5) {
     FormParams.AddrSize = DebugLineData.getU8(Cursor);
-    assert((!Cursor || DebugLineData.getAddressSize() == 0 ||
-            DebugLineData.getAddressSize() == getAddressSize()) &&
-           "Line table header and data extractor disagree");
+    const uint8_t DataAddrSize = DebugLineData.getAddressSize();
+    const uint8_t PrologueAddrSize = FormParams.AddrSize;
+    if (DataAddrSize == 0) {
+      if (PrologueAddrSize != 4 && PrologueAddrSize != 8) {
+        return ReportErrorOrCursor(createStringError(
+            errc::not_supported,
+            "parsing line table prologue at offset 0x%8.8" PRIx64
+            ": invalid address size %" PRIu8, PrologueOffset,
+            PrologueAddrSize));
+      }
+    } else if (DataAddrSize != getAddressSize()) {
+      return ReportErrorOrCursor(createStringError(
+          errc::not_supported,
+          "parsing line table prologue at offset 0x%8.8" PRIx64 ": address "
+          "size %" PRIu8 " doesn't match architecture address size %" PRIu8,
+          PrologueOffset, PrologueAddrSize, DataAddrSize));
+    }
     SegSelectorSize = DebugLineData.getU8(Cursor);
   }
 
diff --git a/llvm/unittests/DebugInfo/DWARF/DWARFDebugLineTest.cpp b/llvm/unittests/DebugInfo/DWARF/DWARFDebugLineTest.cpp
index d42a626fa9c1c..d7d04312a1c4c 100644
--- a/llvm/unittests/DebugInfo/DWARF/DWARFDebugLineTest.cpp
+++ b/llvm/unittests/DebugInfo/DWARF/DWARFDebugLineTest.cpp
@@ -821,15 +821,10 @@ TEST_F(DebugLineBasicFixture, ErrorForUnsupportedAddressSizeDefinedInHeader) {
 
   auto ExpectedLineTable = Line.getOrParseLineTable(LineData, 0, *Context,
                                                     nullptr, RecordRecoverable);
-  EXPECT_THAT_ERROR(
-      std::move(Recoverable),
-      FailedWithMessage("address size 0x09 of DW_LNE_set_address opcode at "
-                        "offset 0x00000038 is unsupported"));
-  ASSERT_THAT_EXPECTED(ExpectedLineTable, Succeeded());
-  ASSERT_EQ((*ExpectedLineTable)->Rows.size(), 3u);
-  EXPECT_EQ((*ExpectedLineTable)->Sequences.size(), 1u);
-  // Show that the set address opcode is ignored in this case.
-  EXPECT_EQ((*ExpectedLineTable)->Rows[0].Address.Address, 0u);
+  ASSERT_THAT_EXPECTED(ExpectedLineTable,
+                       FailedWithMessage("parsing line table prologue at "
+                                         "offset 0x00000000: invalid address "
+                                         "size 9"));
 }
 
 TEST_F(DebugLineBasicFixture, CallbackUsedForUnterminatedSequence) {

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[dwblaikie]

These should be recoverable errors, because we can skip this line table and read the next one.

[clayborg]

I have made the prologue errors recoverable. Anything else needed here?

[JDevlieghere]

LGTM!

[dwblaikie]

Looks like this path isn't tested? Could you add a test?

[dwblaikie]

Looks like this test change removed coverage for a different error message, by failing earlier?

This test should probably be restored by modifying it to be reachable, or the original code's error handling should be turned into an assertion if the diagnostic is now an invariant for the code?