[DebugInfo] Don't crash when given invalid DWARFv5 line table prologue.

[JDevlieghere]

Summary

This patch replaces an assertion with an explicit check for the validity
of the FORM parameters. The assertion was triggered when the DWARFv5
line table contained a zero address size.

This fixes OSS-Fuzz Issue 4644
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=4644

[JDevlieghere]

Paul, Adrian, if you guys think there's a better place to check this, please let me know. This solution felt the most generic, but maybe we can warn about this earlier (& with a more informative message). Does it ever make sense for the address size to be zero?

[probinson]

In a real object file it should never be zero. There are a bunch of places in the unittests where I construct one with version and addrsize both zero; those would have to be fixed if we wanted to have a check somewhere other than for a form that actually cares about that stuff.

[JDevlieghere]

In D41615#964884, @probinson wrote:

In a real object file it should never be zero. There are a bunch of places in the unittests where I construct one with version and addrsize both zero; those would have to be fixed if we wanted to have a check somewhere other than for a form that actually cares about that stuff.

Alternatively we can keep this for a check in the verifier.

[aprantl]

SGTM.

llvm/trunk/include/llvm/DebugInfo/DWARF/DWARFFormValue.h

uint8_t getDwarfOffsetByteSize() const {
     switch (Format) {
     case dwarf::DwarfFormat::DWARF32:
       return 4;
     case dwarf::DwarfFormat::DWARF64:
       return 8;
     }
     llvm_unreachable("Invalid Format value");
   }
+
+  explicit operator bool() const { return Version && AddrSize; }
 };
 
 class DWARFFormValue {
 public:
   enum FormClass {
     FC_Unknown,
     FC_Address,
     FC_Block,

llvm/trunk/lib/DebugInfo/DWARF/DWARFDebugLine.cpp

bool DWARFDebugLine::Prologue::parse(const DWARFDataExtractor &DebugLineData,
   StandardOpcodeLengths.reserve(OpcodeBase - 1);
   for (uint32_t I = 1; I < OpcodeBase; ++I) {
     uint8_t OpLen = DebugLineData.getU8(OffsetPtr);
     StandardOpcodeLengths.push_back(OpLen);
   }
 
   if (getVersion() >= 5) {
     if (!parseV5DirFileTables(DebugLineData, OffsetPtr, EndPrologueOffset,
-                              getFormParams(), U, HasMD5, IncludeDirectories,
+                              FormParams, U, HasMD5, IncludeDirectories,
                               FileNames)) {
       fprintf(stderr,
               "warning: parsing line table prologue at 0x%8.8" PRIx64
               " found an invalid directory or file table description at"
               " 0x%8.8" PRIx64 "\n", PrologueOffset, (uint64_t)*OffsetPtr);
       return false;
     }
   } else

llvm/trunk/lib/DebugInfo/DWARF/DWARFFormValue.cpp

static const DWARFFormValue::FormClass DWARF4FormClasses[] = {
     DWARFFormValue::FC_Flag,          // 0x19 DW_FORM_flag_present
 };
 
 Optional<uint8_t>
 DWARFFormValue::getFixedByteSize(dwarf::Form Form,
                                  const DWARFFormParams Params) {
   switch (Form) {
   case DW_FORM_addr:
-    assert(Params.Version && Params.AddrSize && "Invalid Params for form");
+    if (Params)
       return Params.AddrSize;
+    return None;
 
   case DW_FORM_block:          // ULEB128 length L followed by L bytes.
   case DW_FORM_block1:         // 1 byte length L followed by L bytes.
   case DW_FORM_block2:         // 2 byte length L followed by L bytes.
   case DW_FORM_block4:         // 4 byte length L followed by L bytes.
   case DW_FORM_string:         // C-string with null terminator.
   case DW_FORM_sdata:          // SLEB128.
   case DW_FORM_udata:          // ULEB128.
   case DW_FORM_ref_udata:      // ULEB128.
   case DW_FORM_indirect:       // ULEB128.
   case DW_FORM_exprloc:        // ULEB128 length L followed by L bytes.
   case DW_FORM_strx:           // ULEB128.
   case DW_FORM_addrx:          // ULEB128.
   case DW_FORM_loclistx:       // ULEB128.
   case DW_FORM_rnglistx:       // ULEB128.
   case DW_FORM_GNU_addr_index: // ULEB128.
   case DW_FORM_GNU_str_index:  // ULEB128.
     return None;
 
   case DW_FORM_ref_addr:
-    assert(Params.Version && Params.AddrSize && "Invalid Params for form");
+    if (Params)
       return Params.getRefAddrByteSize();
+    return None;
 
   case DW_FORM_flag:
   case DW_FORM_data1:
   case DW_FORM_ref1:
   case DW_FORM_strx1:
   case DW_FORM_addrx1:
     return 1;
 
case DW_FORM_addrx4:
     return 4;
 
   case DW_FORM_strp:
   case DW_FORM_GNU_ref_alt:
   case DW_FORM_GNU_strp_alt:
   case DW_FORM_line_strp:
   case DW_FORM_sec_offset:
   case DW_FORM_strp_sup:
-    assert(Params.Version && Params.AddrSize && "Invalid Params for form");
+    if (Params)
       return Params.getDwarfOffsetByteSize();
+    return None;
 
   case DW_FORM_data8:
   case DW_FORM_ref8:
   case DW_FORM_ref_sig8:
   case DW_FORM_ref_sup8:
     return 8;
 
   case DW_FORM_flag_present:

llvm/trunk/test/DebugInfo/dwarfdump-invalid-line-table.test

+Verify that dwarfdump doesn't crash on invalid line table prologue.
+OSS-Fuzz Issue 4644 (https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=4644)
+
+RUN: llvm-dwarfdump --verbose %p/Inputs/invalid.linetable 2>&1 | FileCheck %s --check-prefix=INVALID-LINE-TABLE
+INVALID-LINE-TABLE: invalid directory or file table description