[DebugInfo] Dump raw data in a case of decoding error of an expression.

[ikudrin]

Summary

It looks like that was an initial intention, but some code paths in DWARFExpression::Operation::extract() did not initialize EndOffset properly.

[aprantl]

Seems plausible

[MaskRay]

llvm/lib/DebugInfo/DWARF/DWARFExpression.cpp

137

Delete EndOffset = Offset; I added in befbc99a7f092df5868b5ff0c6e46f41236cb1af

llvm/lib/DebugInfo/DWARF/DWARFExpression.cpp

static DWARFExpression::Operation::Description getOpDesc(unsigned OpCode) {
   if (OpCode >= Descriptions.size())
     return {};
   return Descriptions[OpCode];
 }
 
 bool DWARFExpression::Operation::extract(DataExtractor Data,
                                          uint8_t AddressSize, uint64_t Offset,
                                          Optional<DwarfFormat> Format) {
+  EndOffset = Offset;
   Opcode = Data.getU8(&Offset);
 
   Desc = getOpDesc(Opcode);
-  if (Desc.Version == Operation::DwarfNA) {
-    EndOffset = Offset;
+  if (Desc.Version == Operation::DwarfNA)
     return false;
-  }
 
   for (unsigned Operand = 0; Operand < 2; ++Operand) {
     unsigned Size = Desc.Op[Operand];
     unsigned Signed = Size & Operation::SignBit;
 
     if (Size == Operation::SizeNA)
       break;
 
-    EndOffset = Offset;
     switch (Size & ~Operation::SignBit) {
     case Operation::Size1:
       Operands[Operand] = Data.getU8(&Offset);
       if (Signed)
         Operands[Operand] = (int8_t)Operands[Operand];
       break;
     case Operation::Size2:
       Operands[Operand] = Data.getU16(&Offset);
       if (Signed)

llvm/test/DebugInfo/X86/DW_OP_call_ref_unexpected.s

 # RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t.o
 # RUN: llvm-dwarfdump -debug-loc %t.o | FileCheck %s
 
 # This checks that we do not try to interpret DW_OP_call_ref if it is
 # encountered in a location table.
 
 # CHECK: .debug_loc contents:
 # CHECK-NEXT: 0x00000000:
-# CHECK-NEXT:   (0x0000000000000000, 0x0000000000000015): <decoding error>
+# CHECK-NEXT:   (0x0000000000000000, 0x0000000000000015): <decoding error> 9a ff 00 00 00
 
     .section .debug_loc, "", @progbits
     .quad 0                         # Beginning address offset
     .quad 0x15                      # Ending address offset
     .short .LDescrEnd-.LDescrBegin  # Location description length
 .LDescrBegin:
     .byte 0x9a                      # DW_OP_call_ref
     .long 0xff

llvm/test/tools/llvm-dwarfdump/X86/verify_broken_exprloc.s

 # RUN: llvm-mc %s -filetype obj -triple i686-pc-linux -o %t
 
 ## Check we don't crash when parsing invalid expression opcode.
 # RUN: llvm-dwarfdump %t | FileCheck %s
 # CHECK:      DW_TAG_GNU_call_site_parameter
-# CHECK-NEXT:  DW_AT_location  (<decoding error>)
+# CHECK-NEXT:  DW_AT_location  (<decoding error> ff)
 
 ## Check verifier reports an error.
 # RUN: not llvm-dwarfdump -verify %t 2>&1 | FileCheck %s --check-prefix=VERIFY
 # VERIFY:      DIE contains invalid DWARF expression:
 # VERIFY:      DW_TAG_GNU_call_site_parameter
-# VERIFY-NEXT:   DW_AT_location    (<decoding error>)
+# VERIFY-NEXT:   DW_AT_location    (<decoding error> ff)
 
 .section  .debug_info,"",@progbits
   .long  0x12
   .value  0x4
   .long  0
   .byte  0x4
 
   .uleb128 0x1 # DW_TAG_compile_unit [1]