BPF: Support btf_type_tag attribute

A new kind BTF_KIND_TYPE_TAG is defined. The tags associated
with a pointer type are emitted in their IR order as modifiers.
For example, for the following declaration:
  int __tag1 * __tag1 __tag2 *g;
The BTF type chain will look like
  VAR(g) -> __tag1 --> __tag2 -> pointer -> __tag1 -> pointer -> int
In the above "->" means BTF CommonType.Type which indicates
the point-to type.

Differential Revision: https://reviews.llvm.org/D113222

Author: yonghong-song

llvm/lib/Target/BPF/BTF.def

@@ -32,5 +32,6 @@ HANDLE_BTF_KIND(14, VAR)
 HANDLE_BTF_KIND(15, DATASEC)
 HANDLE_BTF_KIND(16, FLOAT)
 HANDLE_BTF_KIND(17, DECL_TAG)
+HANDLE_BTF_KIND(18, TYPE_TAG)
 
 #undef HANDLE_BTF_KIND

llvm/lib/Target/BPF/BTF.h

@@ -113,7 +113,7 @@ struct CommonType {
   /// "Size" tells the size of the type it is describing.
   ///
   /// "Type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
-  /// FUNC, FUNC_PROTO, VAR and DECL_TAG.
+  /// FUNC, FUNC_PROTO, VAR, DECL_TAG and TYPE_TAG.
   /// "Type" is a type_id referring to another type.
   union {
     uint32_t Size;

llvm/lib/Target/BPF/BTFDebug.cpp

@@ -408,6 +408,19 @@ void BTFTypeDeclTag::emitType(MCStreamer &OS) {
   OS.emitInt32(Info);
 }
 
+BTFTypeTypeTag::BTFTypeTypeTag(uint32_t BaseTypeId, StringRef Tag) : Tag(Tag) {
+  Kind = BTF::BTF_KIND_TYPE_TAG;
+  BTFType.Info = Kind << 24;
+  BTFType.Type = BaseTypeId;
+}
+
+void BTFTypeTypeTag::completeType(BTFDebug &BDebug) {
+  if (IsCompleted)
+    return;
+  IsCompleted = true;
+  BTFType.NameOff = BDebug.addString(Tag);
+}
+
 uint32_t BTFStringTable::addString(StringRef S) {
   // Check whether the string already exists.
   for (auto &OffsetM : OffsetToIdMap) {
@@ -658,9 +671,41 @@ void BTFDebug::visitDerivedType(const DIDerivedType *DTy, uint32_t &TypeId,
     }
   }
 
-  if (Tag == dwarf::DW_TAG_pointer_type || Tag == dwarf::DW_TAG_typedef ||
-      Tag == dwarf::DW_TAG_const_type || Tag == dwarf::DW_TAG_volatile_type ||
-      Tag == dwarf::DW_TAG_restrict_type) {
+  if (Tag == dwarf::DW_TAG_pointer_type) {
+    SmallVector<const MDString *, 4> MDStrs;
+    DINodeArray Annots = DTy->getAnnotations();
+    if (Annots) {
+      for (const Metadata *Annotations : Annots->operands()) {
+        const MDNode *MD = cast<MDNode>(Annotations);
+        const MDString *Name = cast<MDString>(MD->getOperand(0));
+        if (!Name->getString().equals("btf_type_tag"))
+          continue;
+        MDStrs.push_back(cast<MDString>(MD->getOperand(1)));
+      }
+    }
+
+    if (MDStrs.size() > 0) {
+      auto TypeEntry = std::make_unique<BTFTypeDerived>(DTy, Tag, false);
+      unsigned TmpTypeId = addType(std::move(TypeEntry));
+      for (unsigned I = MDStrs.size(); I > 0; I--) {
+        const MDString *Value = MDStrs[I - 1];
+        if (I != 1) {
+          auto TypeEntry =
+              std::make_unique<BTFTypeTypeTag>(TmpTypeId, Value->getString());
+          TmpTypeId = addType(std::move(TypeEntry));
+        } else {
+          auto TypeEntry =
+              std::make_unique<BTFTypeTypeTag>(TmpTypeId, Value->getString());
+          TypeId = addType(std::move(TypeEntry), DTy);
+        }
+      }
+    } else {
+      auto TypeEntry = std::make_unique<BTFTypeDerived>(DTy, Tag, false);
+      TypeId = addType(std::move(TypeEntry), DTy);
+    }
+  } else if (Tag == dwarf::DW_TAG_typedef || Tag == dwarf::DW_TAG_const_type ||
+             Tag == dwarf::DW_TAG_volatile_type ||
+             Tag == dwarf::DW_TAG_restrict_type) {
     auto TypeEntry = std::make_unique<BTFTypeDerived>(DTy, Tag, false);
     TypeId = addType(std::move(TypeEntry), DTy);
     if (Tag == dwarf::DW_TAG_typedef)

llvm/lib/Target/BPF/BTFDebug.h

@@ -216,6 +216,14 @@ class BTFTypeDeclTag : public BTFTypeBase {
   void emitType(MCStreamer &OS) override;
 };
 
+class BTFTypeTypeTag : public BTFTypeBase {
+  StringRef Tag;
+
+public:
+  BTFTypeTypeTag(uint32_t BaseTypeId, StringRef Tag);
+  void completeType(BTFDebug &BDebug) override;
+};
+
 /// String table.
 class BTFStringTable {
   /// String table size in bytes.

llvm/test/CodeGen/BPF/BTF/type-tag-var.ll

@@ -0,0 +1,63 @@
+; RUN: llc -march=bpfel -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
+; RUN: llc -march=bpfeb -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
+;
+; Source:
+;   #define __tag1 __attribute__((btf_type_tag("tag1")))
+;   #define __tag2 __attribute__((btf_type_tag("tag2")))
+;   int __tag1 * __tag1 __tag2 *g;
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm test.c
+
+@g = dso_local local_unnamed_addr global i32** null, align 8, !dbg !0
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!12, !13, !14, !15}
+!llvm.ident = !{!16}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "g", scope: !2, file: !3, line: 3, type: !5, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 14.0.0 (https://github.com/llvm/llvm-project.git 077b2e0cf1e97c4d97ca5ceab3ec0192ed11c66e)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/work/tests/llvm/btf_tag_type")
+!4 = !{!0}
+!5 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !6, size: 64, annotations: !10)
+!6 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !7, size: 64, annotations: !8)
+!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!8 = !{!9}
+!9 = !{!"btf_type_tag", !"tag1"}
+!10 = !{!9, !11}
+!11 = !{!"btf_type_tag", !"tag2"}
+
+; CHECK:             .long   0                               # BTF_KIND_PTR(id = 1)
+; CHECK-NEXT:        .long   33554432                        # 0x2000000
+; CHECK-NEXT:        .long   5
+; CHECK-NEXT:        .long   1                               # BTF_KIND_TYPE_TAG(id = 2)
+; CHECK-NEXT:        .long   301989888                       # 0x12000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   6                               # BTF_KIND_TYPE_TAG(id = 3)
+; CHECK-NEXT:        .long   301989888                       # 0x12000000
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   0                               # BTF_KIND_PTR(id = 4)
+; CHECK-NEXT:        .long   33554432                        # 0x2000000
+; CHECK-NEXT:        .long   6
+; CHECK-NEXT:        .long   6                               # BTF_KIND_TYPE_TAG(id = 5)
+; CHECK-NEXT:        .long   301989888                       # 0x12000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   11                              # BTF_KIND_INT(id = 6)
+; CHECK-NEXT:        .long   16777216                        # 0x1000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   16777248                        # 0x1000020
+; CHECK-NEXT:        .long   15                              # BTF_KIND_VAR(id = 7)
+; CHECK-NEXT:        .long   234881024                       # 0xe000000
+; CHECK-NEXT:        .long   3
+; CHECK-NEXT:        .long   1
+
+; CHECK:             .ascii  "tag2"                          # string offset=1
+; CHECK:             .ascii  "tag1"                          # string offset=6
+; CHECK:             .ascii  "int"                           # string offset=11
+; CHECK:             .byte   103                             # string offset=15
+
+!12 = !{i32 7, !"Dwarf Version", i32 4}
+!13 = !{i32 2, !"Debug Info Version", i32 3}
+!14 = !{i32 1, !"wchar_size", i32 4}
+!15 = !{i32 7, !"frame-pointer", i32 2}
+!16 = !{!"clang version 14.0.0 (https://github.com/llvm/llvm-project.git 077b2e0cf1e97c4d97ca5ceab3ec0192ed11c66e)"}