[dwarfdump] Add verifier check to find DIEs with DW_CHILDREN_yes but without children.

[JDevlieghere]

Summary

Flag DIEs that have DW_CHILDREN_yes set in their abbreviation but don't actually have any children.

rdar://59809554

[dblaikie]

does this classify as a warning? Is there a distinction between ill-formed DWARF and "this is valid, but unlikely to be great"?

[JDevlieghere]

In D88048#2286251, @dblaikie wrote:

does this classify as a warning? Is there a distinction between ill-formed DWARF and "this is valid, but unlikely to be great"?

I was on the fence myself, I couldn't find anything conclusive in the standard. I've made it a warning.

[dblaikie]

maybe slightly long test case - could do this with the CU DIE itself? (perhaps a case where hand-crafted/substantially hand-modified assembly is OK, because it can be made /so/ simple - or maybe yaml2obj dwarf support is adequate for this use case?)

[Higuoxing]

In D88048#2286589, @dblaikie wrote:

maybe slightly long test case - could do this with the CU DIE itself? (perhaps a case where hand-crafted/substantially hand-modified assembly is OK, because it can be made /so/ simple - or maybe yaml2obj dwarf support is adequate for this use case?)

Hi, currently, obj2yaml doesn't work properly when dumping the .debug_abbrev/__debug_abbrev section. We might not be able to get the correct output when there are multiple DIEs in one abbrev table. D87179 has fixed it but hasn't been landed yet. I've created one test case for this patch. Hope it works :-)

--- !ELF
FileHeader:
  Class: ELFCLASS64
  Data:  ELFDATA2LSB
  Type:  ET_EXEC
DWARF:
  debug_abbrev:
    - Table:
        - Tag:      DW_TAG_compile_unit
          Children: DW_CHILDREN_yes
          Attributes:
            - Attribute: DW_AT_low_pc
              Form:      DW_FORM_data4
  debug_info:
    - Version: 4
      Entries:
        - AbbrCode: 1
          Values:
            - Value: 0x1234
        - AbbrCode: 0   ## Terminator for the current DIE.

However, it seems that the assertion isValid() && "must check validity prior to calling" is triggered when the DIE isn't terminated.

--- !ELF
FileHeader:
  Class: ELFCLASS64
  Data:  ELFDATA2LSB
  Type:  ET_EXEC
DWARF:
  debug_abbrev:
    - Table:
        - Tag:      DW_TAG_compile_unit
          Children: DW_CHILDREN_yes
          Attributes:
            - Attribute: DW_AT_low_pc
              Form:      DW_FORM_data4
  debug_info:
    - Version: 4
      Entries:
        - AbbrCode: 1
          Values:
            - Value: 0x1234

See my inline comments.

[Higuoxing]

llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp

176

[aprantl]

Warning seems fine to me since it's more an inefficient encoding (an empty list of children) than malformed.

LGTM once everyone else is happy.

[JDevlieghere]

In D88048#2286776, @Higuoxing wrote:

In D88048#2286589, @dblaikie wrote:

maybe slightly long test case - could do this with the CU DIE itself? (perhaps a case where hand-crafted/substantially hand-modified assembly is OK, because it can be made /so/ simple - or maybe yaml2obj dwarf support is adequate for this use case?)

Hi, currently, obj2yaml doesn't work properly when dumping the .debug_abbrev/__debug_abbrev section. We might not be able to get the correct output when there are multiple DIEs in one abbrev table. D87179 has fixed it but hasn't been landed yet. I've created one test case for this patch. Hope it works :-)

(I forgot to submit the comment before landing this)

Awesome, thanks a lot, that's a great test case! :-)

llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp

for (unsigned I = 0; I < NumDies; ++I) {
     if (Die.getTag() == DW_TAG_null)
       continue;
 
     for (auto AttrValue : Die.attributes()) {
       NumUnitErrors += verifyDebugInfoAttribute(Die, AttrValue);
       NumUnitErrors += verifyDebugInfoForm(Die, AttrValue);
     }
 
+    if (Die.hasChildren()) {
+      if (Die.getFirstChild().getTag() == DW_TAG_null) {
+        warn() << dwarf::TagString(Die.getTag())
+               << " has DW_CHILDREN_yes but DIE has no children: ";
+        Die.dump(OS);
+      }
+    }
+
     NumUnitErrors += verifyDebugInfoCallSite(Die);
   }
 
   DWARFDie Die = Unit.getUnitDIE(/* ExtractUnitDIEOnly = */ false);
   if (!Die) {
     error() << "Compilation unit without DIE.\n";
     NumUnitErrors++;
     return NumUnitErrors;

llvm/test/tools/llvm-dwarfdump/X86/no-children.s

+# RUN: llvm-mc %s -filetype obj -triple x86_64-apple-macos -o - \
+# RUN: | llvm-dwarfdump -verify - | FileCheck %s
+
+# CHECK: warning: DW_TAG_module has DW_CHILDREN_yes but DIE has no children:
+# CHECK-NEXT: DW_TAG_module
+# CHECK-NEXT: DW_AT_name        ("Foundation")
+# CHECK-NEXT: DW_AT_LLVM_include_path   ("/SDK/Foundation.swiftmodule/x86_64.swiftinterface")
+
+##; Generated from the following manually stripped empty Swift program:
+##;
+##; target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+##; target triple = "x86_64-apple-macosx10.9.0"
+##;
+##; @__swift_reflection_version = linkonce_odr hidden constant i16 3
+##; @llvm.used = appending global [1 x i8*] [i8* bitcast (i16* @__swift_reflection_version to i8*)], section "llvm.metadata", align 8
+##;
+##; define i32 @main(i32, i8**) !dbg !29 {
+##; entry:
+##;   %2 = bitcast i8** %1 to i8*
+##;   ret i32 0, !dbg !35
+##; }
+##;
+##; !llvm.dbg.cu = !{!0}
+##; !swift.module.flags = !{!14}
+##; !llvm.module.flags = !{!20, !21, !24}
+##;
+##; !0 = distinct !DICompileUnit(language: DW_LANG_Swift, file: !1, isOptimized: false, runtimeVersion: 5, emissionKind: FullDebug, enums: !2, imports: !3, sysroot: "/SDK")
+##; !1 = !DIFile(filename: "ParseableInterfaceImports.swift", directory: "/")
+##; !2 = !{}
+##; !3 = !{!4, !6, !8}
+##; !4 = !DIImportedEntity(tag: DW_TAG_imported_module, scope: !1, entity: !5, file: !1)
+##; !5 = !DIModule(scope: null, name: "Foo", includePath: "/Foo/x86_64.swiftinterface")
+##; !6 = !DIImportedEntity(tag: DW_TAG_imported_module, scope: !1, entity: !7, file: !1)
+##; !7 = !DIModule(scope: null, name: "Swift", includePath: "/SDK/Swift.swiftmodule/x86_64.swiftinterface", sysroot: "/SDK")
+##; !8 = !DIImportedEntity(tag: DW_TAG_imported_module, scope: !1, entity: !7, file: !1)
+##; !9 = !DIModule(scope: null, name: "Foundation", includePath: "/SDK/Foundation.swiftmodu
+##; !14 = !{!"standard-library", i1 false}
+##; !20 = !{i32 2, !"Dwarf Version", i32 4}
+##; !21 = !{i32 2, !"Debug Info Version", i32 3}
+##; !24 = !{i32 1, !"Swift Version", i32 7}
+##; !29 = distinct !DISubprogram(name: "main", linkageName: "main", scope: !5, file: !1, line: 1, type: !30, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+##; !30 = !DISubroutineType(types: !31)
+##; !31 = !{}
+##; !35 = !DILocation(line: 0, scope: !36)
+##; !36 = !DILexicalBlockFile(scope: !29, file: !37, discriminator: 0)
+##; !37 = !DIFile(filename: "<compiler-generated>", directory: "")
+        .section  __TEXT,__text,regular,pure_instructions
+  .macosx_version_min 10, 9
+  .globl  _main                   ## -- Begin function main
+  .p2align  4, 0x90
+_main:                                  ## @main
+Lfunc_begin0:
+  .file 1 "/ParseableInterfaceImports.swift"
+  .loc  1 0 0                   ## ParseableInterfaceImports.swift:0:0
+  .cfi_startproc
+## %bb.0:                               ## %entry
+  xorl  %eax, %eax
+  retq
+Ltmp0:
+Lfunc_end0:
+  .cfi_endproc
+                                        ## -- End function
+  .private_extern ___swift_reflection_version ## @__swift_reflection_version
+  .section  __TEXT,__const
+  .globl  ___swift_reflection_version
+  .weak_definition  ___swift_reflection_version
+  .p2align  1
+___swift_reflection_version:
+  .short  3                       ## 0x3
+
+  .no_dead_strip  ___swift_reflection_version
+  .section  __DWARF,__debug_str,regular,debug
+Linfo_string:
+  .byte 0                       ## string offset=0
+  .asciz  "ParseableInterfaceImports.swift" ## string offset=1
+  .asciz  "/"                     ## string offset=33
+  .asciz  "Foo"                   ## string offset=35
+  .asciz  "/Foo/x86_64.swiftinterface" ## string offset=39
+  .asciz  "Swift"                 ## string offset=66
+  .asciz  "/SDK/Swift.swiftmodule/x86_64.swiftinterface" ## string offset=72
+  .asciz  "/SDK"                  ## string offset=117
+  .asciz  "main"                  ## string offset=122
+        .asciz  "Foundation"            ## string offset=127
+        .asciz  "/SDK/Foundation.swiftmodule/x86_64.swiftinterface" ## string offset=138
+  .section  __DWARF,__debug_abbrev,regular,debug
+Lsection_abbrev:
+  .byte 1                       ## Abbreviation Code
+  .byte 17                      ## DW_TAG_compile_unit
+  .byte 1                       ## DW_CHILDREN_yes
+  .byte 37                      ## DW_AT_producer
+  .byte 14                      ## DW_FORM_strp
+  .byte 19                      ## DW_AT_language
+  .byte 5                       ## DW_FORM_data2
+  .byte 3                       ## DW_AT_name
+  .byte 14                      ## DW_FORM_strp
+        .ascii  "\202|"                 ## DW_AT_LLVM_sysroot
+  .byte 14                      ## DW_FORM_strp
+  .byte 16                      ## DW_AT_stmt_list
+  .byte 23                      ## DW_FORM_sec_offset
+  .byte 27                      ## DW_AT_comp_dir
+  .byte 14                      ## DW_FORM_strp
+  .ascii  "\345\177"              ## DW_AT_APPLE_major_runtime_vers
+  .byte 11                      ## DW_FORM_data1
+  .byte 17                      ## DW_AT_low_pc
+  .byte 1                       ## DW_FORM_addr
+  .byte 18                      ## DW_AT_high_pc
+  .byte 6                       ## DW_FORM_data4
+  .byte 0                       ## EOM(1)
+  .byte 0                       ## EOM(2)
+  .byte 2                       ## Abbreviation Code
+  .byte 30                      ## DW_TAG_module
+  .byte 1                       ## DW_CHILDREN_yes
+  .byte 3                       ## DW_AT_name
+  .byte 14                      ## DW_FORM_strp
+  .ascii  "\200|"                 ## DW_AT_LLVM_include_path
+  .byte 14                      ## DW_FORM_strp
+  .byte 0                       ## EOM(1)
+  .byte 0                       ## EOM(2)
+  .byte 3                       ## Abbreviation Code
+  .byte 46                      ## DW_TAG_subprogram
+  .byte 0                       ## DW_CHILDREN_no
+  .byte 17                      ## DW_AT_low_pc
+  .byte 1                       ## DW_FORM_addr
+  .byte 18                      ## DW_AT_high_pc
+  .byte 6                       ## DW_FORM_data4
+  .ascii  "\347\177"              ## DW_AT_APPLE_omit_frame_ptr
+  .byte 25                      ## DW_FORM_flag_present
+  .byte 64                      ## DW_AT_frame_base
+  .byte 24                      ## DW_FORM_exprloc
+  .byte 110                     ## DW_AT_linkage_name
+  .byte 14                      ## DW_FORM_strp
+  .byte 3                       ## DW_AT_name
+  .byte 14                      ## DW_FORM_strp
+  .byte 58                      ## DW_AT_decl_file
+  .byte 11                      ## DW_FORM_data1
+  .byte 59                      ## DW_AT_decl_line
+  .byte 11                      ## DW_FORM_data1
+  .byte 63                      ## DW_AT_external
+  .byte 25                      ## DW_FORM_flag_present
+  .byte 0                       ## EOM(1)
+  .byte 0                       ## EOM(2)
+  .byte 4                       ## Abbreviation Code
+  .byte 58                      ## DW_TAG_imported_module
+  .byte 0                       ## DW_CHILDREN_no
+  .byte 24                      ## DW_AT_import
+  .byte 19                      ## DW_FORM_ref4
+  .byte 0                       ## EOM(1)
+  .byte 0                       ## EOM(2)
+  .byte 5                       ## Abbreviation Code
+  .byte 30                      ## DW_TAG_module
+  .byte 0                       ## DW_CHILDREN_no
+  .byte 3                       ## DW_AT_name
+  .byte 14                      ## DW_FORM_strp
+  .ascii  "\200|"                 ## DW_AT_LLVM_include_path
+  .byte 14                      ## DW_FORM_strp
+  .ascii  "\202|"                 ## DW_AT_LLVM_sysroot
+  .byte 14                      ## DW_FORM_strp
+  .byte 0                       ## EOM(1)
+  .byte 0                       ## EOM(2)
+  .byte 0                       ## EOM(3)
+  .section  __DWARF,__debug_info,regular,debug
+Lsection_info:
+Lcu_begin0:
+.set Lset0, Ldebug_info_end0-Ldebug_info_start0 ## Length of Unit
+  .long Lset0
+Ldebug_info_start0:
+  .short  4                       ## DWARF version number
+.set Lset1, Lsection_abbrev-Lsection_abbrev ## Offset Into Abbrev. Section
+  .long Lset1
+  .byte 8                       ## Address Size (in bytes)
+  .byte 1                       ## Abbrev [1] 0xb:0x5b DW_TAG_compile_unit
+  .long 0                       ## DW_AT_producer
+  .short  30                      ## DW_AT_language
+  .long 1                       ## DW_AT_name
+        .long 117                     ## DW_AT_name
+.set Lset2, Lline_table_start0-Lsection_line ## DW_AT_stmt_list
+  .long Lset2
+  .long 33                      ## DW_AT_comp_dir
+  .byte 5                       ## DW_AT_APPLE_major_runtime_vers
+  .quad Lfunc_begin0            ## DW_AT_low_pc
+.set Lset3, Lfunc_end0-Lfunc_begin0     ## DW_AT_high_pc
+  .long Lset3
+  .byte 2                       ## Abbrev [2] 0x2b:0x23 DW_TAG_module
+  .long 35                      ## DW_AT_name
+  .long 39                      ## DW_AT_LLVM_include_path
+  .byte 3                       ## Abbrev [3] 0x34:0x19 DW_TAG_subprogram
+  .quad Lfunc_begin0            ## DW_AT_low_pc
+.set Lset4, Lfunc_end0-Lfunc_begin0     ## DW_AT_high_pc
+  .long Lset4
+                                        ## DW_AT_APPLE_omit_frame_ptr
+  .byte 1                       ## DW_AT_frame_base
+  .byte 87
+  .long 122                     ## DW_AT_linkage_name
+  .long 122                     ## DW_AT_name
+  .byte 1                       ## DW_AT_decl_file
+  .byte 1                       ## DW_AT_decl_line
+                                        ## DW_AT_external
+  .byte 0                       ## End Of Children Mark
+  .byte 4                       ## Abbrev [4] 0x4e:0x5 DW_TAG_imported_module
+  .long 47                      ## DW_AT_import
+  .byte 5                       ## Abbrev [5] 0x53:0xd DW_TAG_module
+  .long 66                      ## DW_AT_name
+  .long 72                      ## DW_AT_LLVM_include_path
+  .long 117                     ## DW_AT_LLVM_sysroot
+  .byte 4                       ## Abbrev [4] 0x60:0x5 DW_TAG_imported_module
+  .long 87                      ## DW_AT_import
+  .byte 2                       ## Abbrev [2] 0x2b:0x23 DW_TAG_module
+  .long 127                     ## DW_AT_name
+  .long 138                     ## DW_AT_LLVM_include_path
+  .byte 0                       ## End Of Children Mark
+Ldebug_info_end0:
+.subsections_via_symbols
+  .section  __DWARF,__debug_line,regular,debug
+Lsection_line:
+Lline_table_start0: