From 58bdf8f9a8c3331c6c4d5f631395fb6f786d1e9c Mon Sep 17 00:00:00 2001
From: Eduard Zingerman <eddyz87@gmail.com>
Date: Fri, 6 Jan 2023 22:45:09 -0800
Subject: [PATCH] [BPF] preserve btf_decl_tag for parameters of extern
 functions

Generate DILocalVariable entries for parameters of extern functions,
the "annotations" field of DILocalVariable is used to link
"btf_decl_tag" annotation with the parameter.

Do this only for BPF backend as there are no other users for this
information. Final DWARF is valid as "Appendix A" is very much lax in
what is allowed as attributes for "DW_TAG_formal_parameter":

    DWARF does not in general require that a given debugging information
    entry contain a particular attribute or set of attributes. Instead,
    a DWARF producer is free to generate any, all, or none of the
    attributes ... other attributes ... may also appear in a given
    debugging information entry.

DWARF Debugging Information Format Version 5,
Appendix A: Attributes by Tag Value (Informative)
Page 251, Line 3.

Differential Revision: https://reviews.llvm.org/D140970
---
 clang/lib/CodeGen/CGDebugInfo.cpp                  | 26 ++++++++++++---
 clang/test/CodeGen/bpf-decl-tag-extern-func-args.c | 38 ++++++++++++++++++++++
 2 files changed, 60 insertions(+), 4 deletions(-)
 create mode 100644 clang/test/CodeGen/bpf-decl-tag-extern-func-args.c

diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 62ea222f..6096c92 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -4206,10 +4206,28 @@ void CGDebugInfo::EmitFunctionDecl(GlobalDecl GD, SourceLocation Loc,
     SPFlags |= llvm::DISubprogram::SPFlagOptimized;
 
   llvm::DINodeArray Annotations = CollectBTFDeclTagAnnotations(D);
-  llvm::DISubprogram *SP = DBuilder.createFunction(
-      FDContext, Name, LinkageName, Unit, LineNo,
-      getOrCreateFunctionType(D, FnType, Unit), ScopeLine, Flags, SPFlags,
-      TParamsArray.get(), getFunctionDeclaration(D), nullptr, Annotations);
+  llvm::DISubroutineType *STy = getOrCreateFunctionType(D, FnType, Unit);
+  llvm::DISubprogram *SP =
+      DBuilder.createFunction(FDContext, Name, LinkageName, Unit, LineNo, STy,
+                              ScopeLine, Flags, SPFlags, TParamsArray.get(),
+                              getFunctionDeclaration(D), nullptr, Annotations);
+
+  // Preserve btf_decl_tag attributes for parameters of extern functions
+  // for BPF target. The parameters created in this loop are attached as
+  // DISubprogram's retainedNodes in the subsequent finalizeSubprogram call.
+  if (IsDeclForCallSite && CGM.getTarget().getTriple().isBPF()) {
+    if (auto *FD = dyn_cast<FunctionDecl>(D)) {
+      llvm::DITypeRefArray ParamTypes = STy->getTypeArray();
+      unsigned ArgNo = 1;
+      for (ParmVarDecl *PD : FD->parameters()) {
+        llvm::DINodeArray ParamAnnotations = CollectBTFDeclTagAnnotations(PD);
+        DBuilder.createParameterVariable(
+            SP, PD->getName(), ArgNo, Unit, LineNo, ParamTypes[ArgNo], true,
+            llvm::DINode::FlagZero, ParamAnnotations);
+        ++ArgNo;
+      }
+    }
+  }
 
   if (IsDeclForCallSite)
     Fn->setSubprogram(SP);
diff --git a/clang/test/CodeGen/bpf-decl-tag-extern-func-args.c b/clang/test/CodeGen/bpf-decl-tag-extern-func-args.c
new file mode 100644
index 0000000..370352d
--- /dev/null
+++ b/clang/test/CodeGen/bpf-decl-tag-extern-func-args.c
@@ -0,0 +1,38 @@
+// REQUIRES: bpf-registered-target
+// RUN: %clang -target bpf -S -emit-llvm -g -O2 -o - %s  | FileCheck %s
+
+#define __decl_tag(x) __attribute__((btf_decl_tag(x)))
+
+extern void foo(int aa __decl_tag("aa_tag"), long bb __decl_tag("bb_tag"));
+extern void bar(char cc __decl_tag("cc_tag"));
+extern void buz(int __decl_tag("buz_arg_tag"));
+
+void root(void) {
+  foo(0, 1);
+  bar(0);
+  buz(0);
+}
+// CHECK: [[foo:![0-9]+]] = !DISubprogram(name: "foo", {{.*}}, retainedNodes: [[foo_nodes:![0-9]+]])
+// CHECK: [[foo_nodes]] = !{[[aa:![0-9]+]], [[bb:![0-9]+]]}
+
+// CHECK: [[aa]] = !DILocalVariable(name: "aa", arg: 1, scope: [[foo]], {{.*}}, annotations: [[aa_annot:![0-9]+]])
+// CHECK: [[aa_annot]] = !{[[aa_tag:![0-9]+]]}
+// CHECK: [[aa_tag]] = !{!"btf_decl_tag", !"aa_tag"}
+
+// CHECK: [[bb]] = !DILocalVariable(name: "bb", arg: 2, scope: [[foo]], {{.*}}, annotations: [[bb_annot:![0-9]+]])
+// CHECK: [[bb_annot]] = !{[[bb_tag:![0-9]+]]}
+// CHECK: [[bb_tag]] = !{!"btf_decl_tag", !"bb_tag"}
+
+// CHECK: [[bar:![0-9]+]] = !DISubprogram(name: "bar", {{.*}}, retainedNodes: [[bar_nodes:![0-9]+]])
+// CHECK: [[bar_nodes]] = !{[[cc:![0-9]+]]}
+
+// CHECK: [[cc]] = !DILocalVariable(name: "cc", arg: 1, scope: [[bar]], {{.*}}, annotations: [[cc_annot:![0-9]+]])
+// CHECK: [[cc_annot]] = !{[[cc_tag:![0-9]+]]}
+// CHECK: [[cc_tag]] = !{!"btf_decl_tag", !"cc_tag"}
+
+// CHECK: [[buz:![0-9]+]] = !DISubprogram(name: "buz", {{.*}}, retainedNodes: [[buz_nodes:![0-9]+]])
+// CHECK: [[buz_nodes]] = !{[[buz_arg:![0-9]+]]}
+
+// CHECK: [[buz_arg]] = !DILocalVariable(arg: 1, scope: [[buz]], {{.*}}, annotations: [[buz_arg_annot:![0-9]+]])
+// CHECK: [[buz_arg_annot]] = !{[[buz_arg_tag:![0-9]+]]}
+// CHECK: [[buz_arg_tag]] = !{!"btf_decl_tag", !"buz_arg_tag"}
-- 
2.7.4