[PATCH] D83242: [RFC][BPF] support expr with typedef type for FIELD_EXISTENCE reloc

[Yonghong Song via Phabricator via llvm-commits]

yonghong-song created this revision.
yonghong-song added reviewers: anakryiko, ast.
Herald added subscribers: llvm-commits, cfe-commits, hiraditya.
Herald added projects: clang, LLVM.

[The patch needs more work e.g. to create proper test, to be agreed on interface, etc.]

This patch added support of expression with typedef type
for FIELD_EXISTENCE relocation. This tries to address the 
following use case:

  enum { FIELD_EXISTENCE = 2, };
  typedef unsigned long u64;
  typedef unsigned int u32;
  struct bpf_perf_event_data_kern;
  typedef u64 (*btf_bpf_read_branch_records)(struct bpf_perf_event_data_kern *, void *, u32, u64);
  int test() {
     btf_bpf_read_branch_records a;
     return __builtin_preserve_field_info(a, FIELD_EXISTENCE);
  }

A relocation with a type of typedef 'btf_bpf_read_branch_records' will be
recorded.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D83242

Files:
  clang/lib/CodeGen/CGBuiltin.cpp
  clang/lib/Sema/SemaChecking.cpp
  llvm/lib/Target/BPF/BPFAbstractMemberAccess.cpp


Index: llvm/lib/Target/BPF/BPFAbstractMemberAccess.cpp
===================================================================
--- llvm/lib/Target/BPF/BPFAbstractMemberAccess.cpp
+++ llvm/lib/Target/BPF/BPFAbstractMemberAccess.cpp
@@ -277,7 +277,7 @@
   }
   if (GV->getName().startswith("llvm.bpf.preserve.field.info")) {
     CInfo.Kind = BPFPreserveFieldInfoAI;
-    CInfo.Metadata = nullptr;
+    CInfo.Metadata = Call->getMetadata(LLVMContext::MD_preserve_access_index);
     // Check validity of info_kind as clang did not check this.
     uint64_t InfoKind = getConstant(Call->getArgOperand(1));
     if (InfoKind >= BPFCoreSharedInfo::MAX_FIELD_RELOC_KIND)
@@ -742,6 +742,13 @@
       break;
     }
 
+    if (CInfo.Kind == BPFPreserveFieldInfoAI) {
+      // typedef type.
+      TypeName = std::string(PossibleTypeDef->getName());
+      TypeMeta = PossibleTypeDef;
+      break;
+    }
+
     assert(CInfo.Kind == BPFPreserveArrayAI);
 
     // Array entries will always be consumed for accumulative initial index.
Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -2582,6 +2582,15 @@
     return false;
   }
 
+  // The second argument needs to be a constant int
+  Arg = TheCall->getArg(1);
+  llvm::APSInt Value;
+  if (!Arg->isIntegerConstantExpr(Value, Context)) {
+    Diag(Arg->getBeginLoc(), diag::err_preserve_field_info_not_const)
+        << 2 << Arg->getSourceRange();
+    return true;
+  }
+
   // The first argument needs to be a record field access.
   // If it is an array element access, we delay decision
   // to BPF backend to check whether the access is a
@@ -2590,21 +2599,14 @@
   if (Arg->getType()->getAsPlaceholderType() ||
       (Arg->IgnoreParens()->getObjectKind() != OK_BitField &&
        !dyn_cast<MemberExpr>(Arg->IgnoreParens()) &&
-       !dyn_cast<ArraySubscriptExpr>(Arg->IgnoreParens()))) {
+       !dyn_cast<ArraySubscriptExpr>(Arg->IgnoreParens()) &&
+       // Value 2 here represents reloc kind FIELD_EXISTENCE.
+       (Value != 2 || !Arg->getType()->getAs<TypedefType>()))) {
     Diag(Arg->getBeginLoc(), diag::err_preserve_field_info_not_field)
         << 1 << Arg->getSourceRange();
     return true;
   }
 
-  // The second argument needs to be a constant int
-  Arg = TheCall->getArg(1);
-  llvm::APSInt Value;
-  if (!Arg->isIntegerConstantExpr(Value, Context)) {
-    Diag(Arg->getBeginLoc(), diag::err_preserve_field_info_not_const)
-        << 2 << Arg->getSourceRange();
-    return true;
-  }
-
   TheCall->setType(Context.UnsignedIntTy);
   return false;
 }
Index: clang/lib/CodeGen/CGBuiltin.cpp
===================================================================
--- clang/lib/CodeGen/CGBuiltin.cpp
+++ clang/lib/CodeGen/CGBuiltin.cpp
@@ -10966,11 +10966,17 @@
     ConstantInt *C = cast<ConstantInt>(EmitScalarExpr(E->getArg(1)));
     Value *InfoKind = ConstantInt::get(Int64Ty, C->getSExtValue());
 
+    llvm::DIType *DbgInfo =
+        getDebugInfo()->getOrCreateStandaloneType(E->getArg(0)->getType(),
+                                                  E->getArg(0)->getExprLoc());
+
     // Built the IR for the preserve_field_info intrinsic.
     llvm::Function *FnGetFieldInfo = llvm::Intrinsic::getDeclaration(
         &CGM.getModule(), llvm::Intrinsic::bpf_preserve_field_info,
         {FieldAddr->getType()});
-    return Builder.CreateCall(FnGetFieldInfo, {FieldAddr, InfoKind});
+    CallInst *Fn = Builder.CreateCall(FnGetFieldInfo, {FieldAddr, InfoKind});
+    Fn->setMetadata(LLVMContext::MD_preserve_access_index, DbgInfo);
+    return Fn;
   }
   case BPF::BI__builtin_btf_type_id: {
     Value *FieldVal = nullptr;


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