[DebugInfo] Avoid a crash when parsing an invalid unit header in DWP.

[ikudrin]

Summary

The integrity checks for index entries in DWARFUnitHeader::extract() might cause the function to return before checking the state of an Error object, which leads to a crash in runtime. The patch fixes the issue by moving the checks in a safe place.

[jhenderson]

LGTM. Just wondering, did you consider writing a unittest instead?

llvm/test/DebugInfo/X86/invalid-cu-length-dwp.s

55

Nit: ##

[ikudrin]

• Fixed a comment mark.

[ikudrin]

In D75177#1895006, @jhenderson wrote:

Just wondering, did you consider writing a unittest instead?

Well, as there is no support for these sections in DWARFYAML I suppose the test would not be that expressive as the lit one. Do you want me to try anyway?

llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp

if (FormParams.Version >= 5) {
     FormParams.AddrSize = debug_info.getU8(offset_ptr, &Err);
     // Fake a unit type based on the section type.  This isn't perfect,
     // but distinguishing compile and type units is generally enough.
     if (SectionKind == DW_SECT_TYPES)
       UnitType = DW_UT_type;
     else
       UnitType = DW_UT_compile;
   }
+  if (isTypeUnit()) {
+    TypeHash = debug_info.getU64(offset_ptr, &Err);
+    TypeOffset = debug_info.getUnsigned(
+        offset_ptr, FormParams.getDwarfOffsetByteSize(), &Err);
+  } else if (UnitType == DW_UT_split_compile || UnitType == DW_UT_skeleton)
+    DWOId = debug_info.getU64(offset_ptr, &Err);
+
+  if (errorToBool(std::move(Err)))
+    return false;
+
   if (IndexEntry) {
     if (AbbrOffset)
       return false;
     auto *UnitContrib = IndexEntry->getOffset();
     if (!UnitContrib || UnitContrib->Length != (Length + 4))
       return false;
     auto *AbbrEntry = IndexEntry->getOffset(DW_SECT_ABBREV);
     if (!AbbrEntry)
       return false;
     AbbrOffset = AbbrEntry->Offset;
   }
-  if (isTypeUnit()) {
-    TypeHash = debug_info.getU64(offset_ptr, &Err);
-    TypeOffset = debug_info.getUnsigned(
-        offset_ptr, FormParams.getDwarfOffsetByteSize(), &Err);
-  } else if (UnitType == DW_UT_split_compile || UnitType == DW_UT_skeleton)
-    DWOId = debug_info.getU64(offset_ptr, &Err);
-
-  if (errorToBool(std::move(Err)))
-    return false;
 
   // Header fields all parsed, capture the size of this unit header.
   assert(*offset_ptr - Offset <= 255 && "unexpected header size");
   Size = uint8_t(*offset_ptr - Offset);
 
   // Type offset is unit-relative; should be after the header and before
   // the end of the current unit.
   bool TypeOffsetOK =

llvm/test/DebugInfo/X86/invalid-cu-length-dwp.s

+# RUN: llvm-mc -triple x86_64-unknown-linux %s -filetype=obj -o - | \
+# RUN:   llvm-dwarfdump -debug-info -
+
+## llvm-dwarfdump used to crash with this input because of an invalid size
+## of the compilation unit contribution in the .debug_cu_index section.
+
+    .section .debug_abbrev.dwo, "e", @progbits
+.LAbbrBegin:
+    .uleb128 1                  # Abbreviation Code
+    .uleb128 17                 # DW_TAG_compile_unit
+    .byte 0                     # DW_CHILDREN_no
+    .uleb128 3                  # DW_AT_name
+    .uleb128 8                  # DW_FORM_string
+    .uleb128 0x2131             # DW_AT_GNU_dwo_id
+    .uleb128 7                  # DW_FORM_data8
+    .byte 0                     # EOM(1)
+    .byte 0                     # EOM(2)
+    .byte 0                     # EOM(3)
+.LAbbrEnd:
+
+    .section .debug_info.dwo, "e", @progbits
+.LCUBegin:
+    .long .LCUEnd-.LCUVersion   # Length
+.LCUVersion:
+    .short 4                    # Version
+    .long 0                     # Abbrev offset
+    .byte 4                     # Address size
+    .uleb128 1                  # Abbrev [1] DW_TAG_compile_unit
+    .asciz "a.c"                # DW_AT_name
+    .quad 0x1100001122222222    # DW_AT_GNU_dwo_id
+.LCUEnd:
+
+    .section .debug_cu_index, "", @progbits
+## Header:
+    .short 2                    # Version
+    .space 2                    # Padding
+    .long 2                     # Section count
+    .long 1                     # Unit count
+    .long 4                     # Slot count
+## Hash Table of Signatures:
+    .quad 0
+    .quad 0
+    .quad 0x1100001122222222
+    .quad 0
+## Parallel Table of Indexes:
+    .long 0
+    .long 0
+    .long 1
+    .long 0
+## Table of Section Offsets:
+## Row 0:
+    .long 1                     # DW_SECT_INFO
+    .long 3                     # DW_SECT_ABBREV
+## Row 1:
+    .long .LCUBegin-.debug_info.dwo     # Offset in .debug_info.dwo
+    .long .LAbbrBegin-.debug_abbrev.dwo # Offset in .debug_abbrev.dwo
+## Table of Section Sizes:
+    .long .LCUEnd-.LCUBegin-1           # Size of the contribution in .debug_info.dwo (invalid)
+    .long .LAbbrEnd-.LAbbrBegin