[PATCH] D70696: [DebugInfo] Support to emit debugInfo for extern variables

[Yonghong Song via Phabricator via cfe-commits]

yonghong-song created this revision.
yonghong-song added reviewers: dblaikie, aprantl, RKSimon.
yonghong-song added a project: debug-info.
Herald added subscribers: llvm-commits, cfe-commits, hiraditya.
Herald added projects: clang, LLVM.

Extern variable usage in BPF is different from traditional
pure user space application. Recent discussion in linux bpf 
mailing list has two use cases where debug info types are 
required to use extern variables:

- extern types are required to have a suitable interface in libbpf (bpf loader) to provide kernel config parameters to bpf programs. https://lore.kernel.org/bpf/CAEf4BzYCNo5GeVGMhp3fhysQ=_axAf=23PtwaZs-yAyafmXC9g@mail.gmail.com/T/#t
- extern types are required so kernel bpf verifier can verify program which uses external functions more precisely. This will make later link with actual external function no need to reverify. https://lore.kernel.org/bpf/87eez4odqp.fsf@toke.dk/T/#m8d5c3e87ffe7f2764e02d722cb0d8cbc136880ed

This patch added clang support to emit debuginfo for extern variables
with a TargetInfo hook to enable it. Currently, only BPF target enables
to generate debug info for extern variables. The emission of
such debuginfo is disabled for C++ at this moment since BPF only
supports a subset of C language. Emission with C++ can be enabled
later if an appropriate use case is identified.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D70696

Files:
  clang/include/clang/AST/ASTConsumer.h
  clang/include/clang/Basic/TargetInfo.h
  clang/include/clang/Sema/Sema.h
  clang/lib/Basic/Targets/BPF.h
  clang/lib/CodeGen/CGDebugInfo.cpp
  clang/lib/CodeGen/CGDebugInfo.h
  clang/lib/CodeGen/CodeGenAction.cpp
  clang/lib/CodeGen/CodeGenModule.cpp
  clang/lib/CodeGen/CodeGenModule.h
  clang/lib/CodeGen/ModuleBuilder.cpp
  clang/lib/Sema/Sema.cpp
  clang/lib/Sema/SemaDecl.cpp
  clang/test/CodeGenCXX/debug-info-extern-duplicate-2.c
  clang/test/CodeGenCXX/debug-info-extern-duplicate.c
  clang/test/CodeGenCXX/debug-info-extern-unused.c
  clang/test/CodeGenCXX/debug-info-extern-var-char-2.c
  clang/test/CodeGenCXX/debug-info-extern-var-char.c
  clang/test/CodeGenCXX/debug-info-extern-var-func.c
  clang/test/CodeGenCXX/debug-info-extern-var-multi.c
  llvm/include/llvm/IR/DIBuilder.h
  llvm/lib/IR/DIBuilder.cpp
  llvm/lib/IR/DebugInfo.cpp
  llvm/unittests/Transforms/Utils/CloningTest.cpp

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