[PATCH] D143966: [DebugInfo][BPF] Add 'annotations' field for DIBasicType & DISubroutineType

[Eduard Zingerman via Phabricator via llvm-commits]

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eddyz87 retitled this revision from "[DebugInfo][BPF] 'annotations' field for DIBasicType & DISubroutineType" to "[DebugInfo][BPF] Add 'annotations' field for DIBasicType & DISubroutineType".
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- Added tests for 'annotations' DWARF field generation for DIBasicType and DISubroutineType.
- Fix for DIBasicType::getImpl() to correctly handle Annotations field.
- Fix for `DwarfUnit::constructTypeDIE(... DIBasicType *BTy)` to generate annotations for dwarf::DW_TAG_unspecified_type instances.


eddyz87 added a comment.

Rebase


eddyz87 added a comment.

Rebase, change for tag name from btf_type_tag:v2 to btf:type_tag.


eddyz87 added a comment.

Fix for LLVMIR compilation error.


eddyz87 added a comment.

Another rebase, hope to fix windows build issue.


eddyz87 added a comment.

Rebase.


Extend `DIBasicType` and `DISubroutineType` with additional field 'annotations', e.g. as below:

  !5 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed, annotations: !6)
  !6 = !{!7}
  !7 = !{!"btf_type_tag", !"tag1"}

These fields would be used by BPF backend to generate DWARF attributes corresponding to `btf_type_tag` type attributes, e.g.:

  0x00000029:   DW_TAG_base_type
                  DW_AT_name	("int")
                  DW_AT_encoding	(DW_ATE_signed)
                  DW_AT_byte_size	(0x04)
  
  0x0000002d:     DW_TAG_LLVM_annotation
                    DW_AT_name	("btf_type_tag")
                    DW_AT_const_value	("tag1")

Such DWARF entries would be used to generate BTF definitions by tools like pahole <https://github.com/acmel/dwarves>.

Note: similar fields with similar purposes are already present in `DIDerivedType` and `DICompositeType`.

Currently `btf_type_tag` attributes are represented in debug information as `annotations` fields in `DIDerivedType` with `DW_TAG_pointer_type tag`. The annotation on a pointer corresponds to pointee having the attributes in the final BTF.

The discussion <https://lore.kernel.org/bpf/87r0w9jjoq.fsf@oracle.com/> at Kernel BPF mailing list came to conclusion, that such annotations should apply to the annotated type itself.
Hence the necessity to extend `DIBasicType` and `DISubroutineType` types with `annotations` field to represent cases like below:

  int __attribute__((btf_type_tag("foo"))) bar;


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D143966

Files:
  llvm/include/llvm/IR/DebugInfoMetadata.h
  llvm/lib/AsmParser/LLParser.cpp
  llvm/lib/Bitcode/Reader/MetadataLoader.cpp
  llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
  llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
  llvm/lib/IR/AsmWriter.cpp
  llvm/lib/IR/DebugInfoMetadata.cpp
  llvm/lib/IR/LLVMContextImpl.h
  llvm/test/Bitcode/attr-btf_tag-dibasic.ll
  llvm/test/Bitcode/attr-btf_tag-disubroutine.ll
  llvm/test/DebugInfo/attr-btf_type_tag.ll

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