[DWARF] Fix a parsing issue with type unit headers.

Reviewers: dblaikie

Differential Revision: https://reviews.llvm.org/D32987

llvm-svn: 302574

llvm/lib/DebugInfo/DWARF/DWARFTypeUnit.cpp

@@ -24,7 +24,11 @@ bool DWARFTypeUnit::extractImpl(DataExtractor debug_info,
     return false;
   TypeHash = debug_info.getU64(offset_ptr);
   TypeOffset = debug_info.getU32(offset_ptr);
-  return TypeOffset < getLength();
+  // TypeOffset is relative to the beginning of the header,
+  // so we have to account for the leading length field.
+  // FIXME: The size of the length field is 12 in DWARF64.
+  unsigned SizeOfLength = 4;
+  return TypeOffset < getLength() + SizeOfLength;
 }
 
 void DWARFTypeUnit::dump(raw_ostream &OS, bool SummarizeTypes) {

llvm/test/DebugInfo/Inputs/typeunit-header.s

@@ -0,0 +1,49 @@
+# Test object with an artifically constructed type unit header to verify 
+# that the length field is correctly used to verify the validity of the
+# type_offset field.
+#
+# To generate the test object:
+# llvm-mc -triple x86_64-unknown-linux typeunit-header.s -filetype=obj \
+#         -o typeunit-header.elf-x86-64
+#
+# We only have an abbreviation for the type unit die which is all we need.
+# Real type unit dies have quite different attributes of course, but we
+# just need to demonstrate an issue with validating length, so we just give it
+# a single visibility attribute.
+        .section .debug_abbrev,"",@progbits
+        .byte 0x01  # Abbrev code
+        .byte 0x41  # DW_TAG_type_unit
+        .byte 0x01  # DW_CHILDREN_yes
+        .byte 0x17  # DW_AT_visibility
+        .byte 0x0b  # DW_FORM_data1
+        .byte 0x00  # EOM(1)
+        .byte 0x00  # EOM(2)
+        .byte 0x02  # Abbrev code
+        .byte 0x13  # DW_TAG_structure_type
+        .byte 0x00  # DW_CHILDREN_no (no members)
+        .byte 0x17  # DW_AT_visibility
+        .byte 0x0b  # DW_FORM_data1
+        .byte 0x00  # EOM(1)
+        .byte 0x00  # EOM(2)
+        .byte 0x00  # EOM(3)
+        
+        .section .debug_types,"",@progbits
+# DWARF v4 Type unit header - DWARF32 format.
+TU_4_32_start:
+        .long TU_4_32_end-TU_4_32_version  # Length of Unit
+TU_4_32_version:
+        .short 4               # DWARF version number
+        .long .debug_abbrev    # Offset Into Abbrev. Section
+        .byte 8                # Address Size (in bytes)
+        .quad 0x0011223344556677 # Type Signature
+        .long TU_4_32_type-TU_4_32_start # Type offset
+# The type-unit DIE, which has just a visibility attribute.
+        .byte 1                # Abbreviation code
+        .byte 1                # DW_VIS_local
+# The type DIE, which also just has a one-byte visibility attribute.
+TU_4_32_type:
+        .byte 2                # Abbreviation code
+        .byte 1                # DW_VIS_local
+        .byte 0 # NULL
+        .byte 0 # NULL
+TU_4_32_end:

llvm/test/DebugInfo/typeunit-header.test

@@ -0,0 +1,15 @@
+RUN: llvm-dwarfdump %p/Inputs/typeunit-header.elf-x86-64 | FileCheck %s
+
+This is testing a bugfix where parsing the type unit header was not 
+taking the unit's intial length field into account when validating.
+
+The input file is hand-coded assembler to generate a type unit stub,
+which only contains a type unit DIE with a sole visibility attribute.
+
+We make sure that llvm-dwarfdump is parsing the type unit header correctly
+and displays it. 
+
+CHECK: .debug_types contents:
+CHECK: 0x00000000: Type Unit: length = 0x00000019 version = 0x0004 abbr_offset = 0x0000 addr_size = 0x08 name = '' type_signature = 0x0011223344556677 type_offset = 0x0019 (next unit at 0x0000001d)
+CHECK: 0x00000017: DW_TAG_type_unit [1] *
+CHECK: DW_AT_visibility [DW_FORM_data1] (DW_VIS_local)