[BPF] generate BTF_KIND_VARs for all non-static globals

[yonghong-song]

Summary

Enable to generate BTF_KIND_VARs for non-static default-section globals which is not allowed previously. Modified the existing test case to accommodate the new change.

Also removed unused linkage enum members VAR_GLOBAL_TENTATIVE and
VAR_GLOBAL_EXTERNAL.

[anakryiko]

looks good, thanks!

llvm/lib/Target/BPF/BTF.h

struct BTFParam {
   uint32_t NameOff;
   uint32_t Type;
 };
 
 /// Variable scoping information.
 enum : uint8_t {
   VAR_STATIC = 0,           ///< Linkage: InternalLinkage
   VAR_GLOBAL_ALLOCATED = 1, ///< Linkage: ExternalLinkage
-  VAR_GLOBAL_TENTATIVE = 2, ///< Linkage: CommonLinkage
-  VAR_GLOBAL_EXTERNAL = 3,  ///< Linkage: ExternalLinkage
 };
 
 /// BTF_KIND_DATASEC are followed by multiple "struct BTFDataSecVar".
 /// The exist number of BTFDataSec is stored in the vlen (of the info
 /// in "struct CommonType").
 struct BTFDataSec {
   uint32_t Type;   ///< A BTF_KIND_VAR type
   uint32_t Offset; ///< In-section offset

llvm/lib/Target/BPF/BTFDebug.cpp

if (Global.hasSection()) {
         SecName = Global.getInitializer()->isZeroValue() ? ".bss" : ".data";
     }
 
     if (ProcessingMapDef != SecName.startswith(".maps"))
       continue;
 
     SmallVector<DIGlobalVariableExpression *, 1> GVs;
     Global.getDebugInfo(GVs);
+
+    // No type information, mostly internal, skip it.
+    if (GVs.size() == 0)
+      continue;
+
     uint32_t GVTypeId = 0;
     for (auto *GVE : GVs) {
       if (SecName.startswith(".maps"))
         visitMapDefType(GVE->getVariable()->getType(), GVTypeId);
       else
         visitTypeEntry(GVE->getVariable()->getType(), GVTypeId, false, false);
       break;
     }
 
     // Only support the following globals:
     //  . static variables
-    //  . non-static global variables with section attributes
+    //  . non-static global variables
     // Essentially means:
     //  . .bcc/.data/.rodata DataSec entities only contain static data
     //  . Other DataSec entities contain static or initialized global data.
     //    Initialized global data are mostly used for finding map key/value type
     //    id's. Whether DataSec is readonly or not can be found from
     //    corresponding ELF section flags.
     auto Linkage = Global.getLinkage();
     if (Linkage != GlobalValue::InternalLinkage &&
-        (Linkage != GlobalValue::ExternalLinkage || !Global.hasSection()))
+        Linkage != GlobalValue::ExternalLinkage)
       continue;
 
     uint32_t GVarInfo = Linkage == GlobalValue::ExternalLinkage
                             ? BTF::VAR_GLOBAL_ALLOCATED
                             : BTF::VAR_STATIC;
     auto VarEntry =
         std::make_unique<BTFKindVar>(Global.getName(), GVTypeId, GVarInfo);
     uint32_t VarId = addType(std::move(VarEntry));

llvm/test/CodeGen/BPF/BTF/global-var-inited.ll

 ; 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 code:
 ;   int a = 3;
 ; Compilation flag:
 ;   clang -target bpf -O2 -g -S -emit-llvm test.c
 
 @a = dso_local local_unnamed_addr global i32 3, align 4, !dbg !0
 
 ; CHECK:             .section        .BTF,"",@progbits
 ; CHECK-NEXT:        .short  60319                   # 0xeb9f
 ; CHECK-NEXT:        .byte   1
 ; CHECK-NEXT:        .byte   0
 ; CHECK-NEXT:        .long   24
 ; CHECK-NEXT:        .long   0
-; CHECK-NEXT:        .long   16
-; CHECK-NEXT:        .long   16
-; CHECK-NEXT:        .long   5
+; CHECK-NEXT:        .long   56
+; CHECK-NEXT:        .long   56
+; CHECK-NEXT:        .long   13
 ; CHECK-NEXT:        .long   1                       # BTF_KIND_INT(id = 1)
 ; CHECK-NEXT:        .long   16777216                # 0x1000000
 ; CHECK-NEXT:        .long   4
 ; CHECK-NEXT:        .long   16777248                # 0x1000020
+; CHECK-NEXT:        .long   5                       # BTF_KIND_VAR(id = 2)
+; CHECK-NEXT:        .long   234881024               # 0xe000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   7                       # BTF_KIND_DATASEC(id = 3)
+; CHECK-NEXT:        .long   251658241               # 0xf000001
+; CHECK-NEXT:        .long   0
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   a
+; CHECK-NEXT:        .long   4
 ; CHECK-NEXT:        .byte   0                       # string offset=0
 ; CHECK-NEXT:        .ascii  "int"                   # string offset=1
 ; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .byte   97                      # string offset=5
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  ".data"                 # string offset=7
+; CHECK-NEXT:        .byte   0
 
 !llvm.dbg.cu = !{!2}
 !llvm.module.flags = !{!7, !8, !9}
 !llvm.ident = !{!10}
 
 !0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
 !1 = distinct !DIGlobalVariable(name: "a", scope: !2, file: !3, line: 1, type: !6, isLocal: false, isDefinition: true)
 !2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 8.0.20181009 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, nameTableKind: None)
 !3 = !DIFile(filename: "test.c", directory: "/home/yhs/work/tests/llvm/bug")
 !4 = !{}
 !5 = !{!0}
 !6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
 !7 = !{i32 2, !"Dwarf Version", i32 4}
 !8 = !{i32 2, !"Debug Info Version", i32 3}
 !9 = !{i32 1, !"wchar_size", i32 4}
 !10 = !{!"clang version 8.0.20181009 "}