[BPF] Support to emit debugInfo for extern variables

[yonghong-song]

Summary

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=[e-mail]/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/[e-mail]/T/#m8d5c3e87ffe7f2764e02d722cb0d8cbc136880ed

This patch added bpf support to consume such info into BTF,
which can then be used by bpf loader. Function processFuncPrototypes()
only adds extern function definitions into BTF. The functions
with actual definition have been added to BTF in some other places.

[yonghong-song]

The corresponding clang/llvm patch which generates debuginfo for extern variables. https://reviews.llvm.org/D70696

[ast]

clang side will expose debuginfo for extern variables and functions, while the backend support is for functions only? Or I'm misreading the patch.

[yonghong-song]

The backend supports extern variable debug info as well. The following restrictions in the old code is removed.

 -    // Ignore external globals for now.
-    if (!Global.hasInitializer() && Global.hasExternalLinkage())
-      continue;

[yonghong-song]

additional test case is added to ensure debuginfo for externs is indeed generated in BTF.

[ast]

got it. lgtm

[yonghong-song]

extern variables can have attribute((weak)) attribute. Support it as well.

[ast]

thanks for adding extra tests

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_EXTERNAL = 2,  ///< 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.h

class BTFDebug : public DebugHandlerBase {
 
   /// Construct a line info.
   void constructLineInfo(const DISubprogram *SP, MCSymbol *Label, uint32_t Line,
                          uint32_t Column);
 
   /// Generate types and variables for globals.
   void processGlobals(bool ProcessingMapDef);
 
+  /// Generate types for function prototypes.
+  void processFuncPrototypes();
+
   /// Generate one offset relocation record.
   void generateFieldReloc(const MachineInstr *MI, const MCSymbol *ORSym,
                            DIType *RootTy, StringRef AccessPattern);
 
   /// Populating unprocessed struct type.
   unsigned populateStructType(const DIType *Ty);
 
   /// Process LD_imm64 instructions.

llvm/lib/Target/BPF/BTFDebug.cpp

void BTFDebug::beginInstruction(const MachineInstr *MI) {
   LineInfoGenerated = true;
   PrevInstLoc = DL;
 }
 
 void BTFDebug::processGlobals(bool ProcessingMapDef) {
   // Collect all types referenced by globals.
   const Module *M = MMI->getModule();
   for (const GlobalVariable &Global : M->globals()) {
-    // Ignore external globals for now.
-    if (!Global.hasInitializer() && Global.hasExternalLinkage())
-      continue;
-
     // Decide the section name.
     StringRef SecName;
     if (Global.hasSection()) {
       SecName = Global.getSection();
-    } else {
+    } else if (Global.hasInitializer()) {
       // data, bss, or readonly sections
       if (Global.isConstant())
         SecName = ".rodata";
       else
         SecName = Global.getInitializer()->isZeroValue() ? ".bss" : ".data";
     }
 
     if (ProcessingMapDef != SecName.startswith(".maps"))
for (auto *GVE : GVs) {
       else
         visitTypeEntry(GVE->getVariable()->getType(), GVTypeId, false, false);
       break;
     }
 
     // Only support the following globals:
     //  . static variables
     //  . non-static weak or non-weak 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.
+    //  . weak or non-weak extern global variables
+    // Whether DataSec is readonly or not can be found from corresponding ELF
+    // section flags. Whether a BTF_KIND_VAR is a weak symbol or not
+    // can be found from the corresponding ELF symbol table.
     auto Linkage = Global.getLinkage();
     if (Linkage != GlobalValue::InternalLinkage &&
         Linkage != GlobalValue::ExternalLinkage &&
-        Linkage != GlobalValue::WeakAnyLinkage)
+        Linkage != GlobalValue::WeakAnyLinkage &&
+        Linkage != GlobalValue::ExternalWeakLinkage)
       continue;
 
-    uint32_t GVarInfo = Linkage == GlobalValue::InternalLinkage
-                            ? BTF::VAR_STATIC
-                            : BTF::VAR_GLOBAL_ALLOCATED;
+    uint32_t GVarInfo;
+    if (Linkage == GlobalValue::InternalLinkage) {
+      GVarInfo = BTF::VAR_STATIC;
+    } else if (Global.hasInitializer()) {
+      GVarInfo = BTF::VAR_GLOBAL_ALLOCATED;
+    } else {
+      GVarInfo = BTF::VAR_GLOBAL_EXTERNAL;
+    }
+
     auto VarEntry =
         std::make_unique<BTFKindVar>(Global.getName(), GVTypeId, GVarInfo);
     uint32_t VarId = addType(std::move(VarEntry));
 
+    if (SecName.empty())
+      continue;
+
     // Find or create a DataSec
     if (DataSecEntries.find(SecName) == DataSecEntries.end()) {
       DataSecEntries[SecName] = std::make_unique<BTFKindDataSec>(Asm, SecName);
     }
 
     // Calculate symbol size
     const DataLayout &DL = Global.getParent()->getDataLayout();
     uint32_t Size = DL.getTypeAllocSize(Global.getType()->getElementType());
if (MO.isGlobal()) {
         OutMI.addOperand(MCOperand::createImm(Imm));
         return true;
       }
     }
   }
   return false;
 }
 
+void BTFDebug::processFuncPrototypes() {
+  const Module *M = MMI->getModule();
+  for (const Function &F : M->functions()) {
+    const DISubprogram *SP = F.getSubprogram();
+    if (!SP || SP->isDefinition())
+      continue;
+
+    uint32_t ProtoTypeId;
+    const std::unordered_map<uint32_t, StringRef> FuncArgNames;
+    visitSubroutineType(SP->getType(), false, FuncArgNames, ProtoTypeId);
+
+    auto VarEntry =
+        std::make_unique<BTFKindVar>(SP->getName(), ProtoTypeId,
+                                     BTF::VAR_GLOBAL_EXTERNAL);
+    uint32_t VarId = addType(std::move(VarEntry));
+
+    StringRef SecName = F.getSection();
+    if (SecName.empty())
+      continue;
+
+    if (DataSecEntries.find(SecName) == DataSecEntries.end()) {
+      DataSecEntries[SecName] = std::make_unique<BTFKindDataSec>(Asm, SecName);
+    }
+
+    DataSecEntries[SecName]->addVar(VarId, Asm->getSymbol(&F), 8);
+  }
+}
+
 void BTFDebug::endModule() {
   // Collect MapDef globals if not collected yet.
   if (MapDefNotCollected) {
     processGlobals(true);
     MapDefNotCollected = false;
   }
 
   // Collect global types/variables except MapDef globals.
   processGlobals(false);
+
+  processFuncPrototypes();
+
   for (auto &DataSec : DataSecEntries)
     addType(std::move(DataSec.second));
 
   // Fixups
   for (auto &Fixup : FixupDerivedTypes) {
     StringRef TypeName = Fixup.first;
     bool IsUnion = Fixup.second.first;
 

llvm/test/CodeGen/BPF/BTF/extern-var-func-weak-section.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:
+;   extern int global_func(char c) __attribute__((weak, section("abc")));
+;   int test() {
+;      return global_func(0);
+;   }
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm test.c
+
+; Function Attrs: nounwind
+define dso_local i32 @test() local_unnamed_addr #0 !dbg !13 {
+entry:
+  %call = tail call i32 @global_func(i8 signext 0) #2, !dbg !16
+  ret i32 %call, !dbg !17
+}
+declare !dbg !4 extern_weak dso_local i32 @global_func(i8 signext) local_unnamed_addr #1 section "abc"
+
+; 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   116
+; CHECK-NEXT:        .long   116
+; CHECK-NEXT:        .long   76
+; CHECK-NEXT:        .long   0                       # BTF_KIND_FUNC_PROTO(id = 1)
+; CHECK-NEXT:        .long   218103808               # 0xd000000
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   1                       # BTF_KIND_INT(id = 2)
+; CHECK-NEXT:        .long   16777216                # 0x1000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   16777248                # 0x1000020
+; CHECK-NEXT:        .long   5                       # BTF_KIND_FUNC(id = 3)
+; CHECK-NEXT:        .long   201326592               # 0xc000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   0                       # BTF_KIND_FUNC_PROTO(id = 4)
+; CHECK-NEXT:        .long   218103809               # 0xd000001
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   0
+; CHECK-NEXT:        .long   5
+; CHECK-NEXT:        .long   55                      # BTF_KIND_INT(id = 5)
+; CHECK-NEXT:        .long   16777216                # 0x1000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   16777224                # 0x1000008
+; CHECK-NEXT:        .long   60                      # BTF_KIND_VAR(id = 6)
+; CHECK-NEXT:        .long   234881024               # 0xe000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   72                      # BTF_KIND_DATASEC(id = 7)
+; CHECK-NEXT:        .long   251658241               # 0xf000001
+; CHECK-NEXT:        .long   0
+; CHECK-NEXT:        .long   6
+; CHECK-NEXT:        .long   global_func
+; CHECK-NEXT:        .long   8
+; CHECK-NEXT:        .byte   0                       # string offset=0
+; CHECK-NEXT:        .ascii  "int"                   # string offset=1
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "test"                  # string offset=5
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  ".text"                 # string offset=10
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "/tmp/home/yhs/work/tests/extern/test.c" # string offset=16
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "char"                  # string offset=55
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "global_func"           # string offset=60
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "abc"                   # string offset=72
+; CHECK-NEXT:        .byte   0
+
+attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!9, !10, !11}
+!llvm.ident = !{!12}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0 (https://github.com/llvm/llvm-project.git 71a9518c93fe1dce9611c24bc707e5baf1f39f0d)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None)
+!1 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/work/tests/extern")
+!2 = !{}
+!3 = !{!4}
+!4 = !DISubprogram(name: "global_func", scope: !1, file: !1, line: 1, type: !5, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
+!5 = !DISubroutineType(types: !6)
+!6 = !{!7, !8}
+!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!8 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
+!9 = !{i32 7, !"Dwarf Version", i32 4}
+!10 = !{i32 2, !"Debug Info Version", i32 3}
+!11 = !{i32 1, !"wchar_size", i32 4}
+!12 = !{!"clang version 10.0.0 (https://github.com/llvm/llvm-project.git 71a9518c93fe1dce9611c24bc707e5baf1f39f0d)"}
+!13 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 2, type: !14, scopeLine: 2, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!14 = !DISubroutineType(types: !15)
+!15 = !{!7}
+!16 = !DILocation(line: 3, column: 11, scope: !13)
+!17 = !DILocation(line: 3, column: 4, scope: !13)

llvm/test/CodeGen/BPF/BTF/extern-var-func-weak.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:
+;   extern int global_func(char c) __attribute__((weak));
+;   int test() {
+;     return global_func(0);
+;   }
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm test.c
+
+; Function Attrs: nounwind
+define dso_local i32 @test() local_unnamed_addr #0 !dbg !13 {
+entry:
+  %call = tail call i32 @global_func(i8 signext 0) #2, !dbg !16
+  ret i32 %call, !dbg !17
+}
+declare !dbg !4 extern_weak dso_local i32 @global_func(i8 signext) local_unnamed_addr #1
+
+; 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   92
+; CHECK-NEXT:        .long   92
+; CHECK-NEXT:        .long   72
+; CHECK-NEXT:        .long   0                       # BTF_KIND_FUNC_PROTO(id = 1)
+; CHECK-NEXT:        .long   218103808               # 0xd000000
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   1                       # BTF_KIND_INT(id = 2)
+; CHECK-NEXT:        .long   16777216                # 0x1000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   16777248                # 0x1000020
+; CHECK-NEXT:        .long   5                       # BTF_KIND_FUNC(id = 3)
+; CHECK-NEXT:        .long   201326592               # 0xc000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   0                       # BTF_KIND_FUNC_PROTO(id = 4)
+; CHECK-NEXT:        .long   218103809               # 0xd000001
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   0
+; CHECK-NEXT:        .long   5
+; CHECK-NEXT:        .long   55                      # BTF_KIND_INT(id = 5)
+; CHECK-NEXT:        .long   16777216                # 0x1000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   16777224                # 0x1000008
+; CHECK-NEXT:        .long   60                      # BTF_KIND_VAR(id = 6)
+; CHECK-NEXT:        .long   234881024               # 0xe000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .byte   0                       # string offset=0
+; CHECK-NEXT:        .ascii  "int"                   # string offset=1
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "test"                  # string offset=5
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  ".text"                 # string offset=10
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "/tmp/home/yhs/work/tests/extern/test.c" # string offset=16
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "char"                  # string offset=55
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "global_func"           # string offset=60
+; CHECK-NEXT:        .byte   0
+
+attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!9, !10, !11}
+!llvm.ident = !{!12}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0 (https://github.com/llvm/llvm-project.git 71a9518c93fe1dce9611c24bc707e5baf1f39f0d)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None)
+!1 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/work/tests/extern")
+!2 = !{}
+!3 = !{!4}
+!4 = !DISubprogram(name: "global_func", scope: !1, file: !1, line: 1, type: !5, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
+!5 = !DISubroutineType(types: !6)
+!6 = !{!7, !8}
+!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!8 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
+!9 = !{i32 7, !"Dwarf Version", i32 4}
+!10 = !{i32 2, !"Debug Info Version", i32 3}
+!11 = !{i32 1, !"wchar_size", i32 4}
+!12 = !{!"clang version 10.0.0 (https://github.com/llvm/llvm-project.git 71a9518c93fe1dce9611c24bc707e5baf1f39f0d)"}
+!13 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 2, type: !14, scopeLine: 2, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!14 = !DISubroutineType(types: !15)
+!15 = !{!7}
+!16 = !DILocation(line: 3, column: 11, scope: !13)
+!17 = !DILocation(line: 3, column: 4, scope: !13)

llvm/test/CodeGen/BPF/BTF/extern-var-func.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:
+;   extern int global_func(char c);
+;   int test() {
+;     return global_func(0);
+;   }
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm test.c
+
+; Function Attrs: nounwind
+define dso_local i32 @test() local_unnamed_addr #0 !dbg !13 {
+entry:
+  %call = tail call i32 @global_func(i8 signext 0) #2, !dbg !16
+  ret i32 %call, !dbg !17
+}
+
+; 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   92
+; CHECK-NEXT:        .long   92
+; CHECK-NEXT:        .long   72
+; CHECK-NEXT:        .long   0                       # BTF_KIND_FUNC_PROTO(id = 1)
+; CHECK-NEXT:        .long   218103808               # 0xd000000
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   1                       # BTF_KIND_INT(id = 2)
+; CHECK-NEXT:        .long   16777216                # 0x1000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   16777248                # 0x1000020
+; CHECK-NEXT:        .long   5                       # BTF_KIND_FUNC(id = 3)
+; CHECK-NEXT:        .long   201326592               # 0xc000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   0                       # BTF_KIND_FUNC_PROTO(id = 4)
+; CHECK-NEXT:        .long   218103809               # 0xd000001
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   0
+; CHECK-NEXT:        .long   5
+; CHECK-NEXT:        .long   55                      # BTF_KIND_INT(id = 5)
+; CHECK-NEXT:        .long   16777216                # 0x1000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   16777224                # 0x1000008
+; CHECK-NEXT:        .long   60                      # BTF_KIND_VAR(id = 6)
+; CHECK-NEXT:        .long   234881024               # 0xe000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .byte   0                       # string offset=0
+; CHECK-NEXT:        .ascii  "int"                   # string offset=1
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "test"                  # string offset=5
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  ".text"                 # string offset=10
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "/tmp/home/yhs/work/tests/extern/test.c" # string offset=16
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "char"                  # string offset=55
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "global_func"           # string offset=60
+; CHECK-NEXT:        .byte   0
+
+declare !dbg !4 dso_local i32 @global_func(i8 signext) local_unnamed_addr #1
+
+attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!9, !10, !11}
+!llvm.ident = !{!12}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0 (https://github.com/llvm/llvm-project.git 77e5c60f04c4597ba5704d3cee61c6d359404ccd)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None)
+!1 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/work/tests/extern")
+!2 = !{}
+!3 = !{!4}
+!4 = !DISubprogram(name: "global_func", scope: !1, file: !1, line: 1, type: !5, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
+!5 = !DISubroutineType(types: !6)
+!6 = !{!7, !8}
+!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!8 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
+!9 = !{i32 2, !"Dwarf Version", i32 4}
+!10 = !{i32 2, !"Debug Info Version", i32 3}
+!11 = !{i32 1, !"wchar_size", i32 4}
+!12 = !{!"clang version 10.0.0 (https://github.com/llvm/llvm-project.git 77e5c60f04c4597ba5704d3cee61c6d359404ccd)"}
+!13 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 2, type: !14, scopeLine: 2, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!14 = !DISubroutineType(types: !15)
+!15 = !{!7}
+!16 = !DILocation(line: 3, column: 10, scope: !13)
+!17 = !DILocation(line: 3, column: 3, scope: !13)

llvm/test/CodeGen/BPF/BTF/extern-var-section.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:
+;   extern int global_func(char c) __attribute__((section("abc")));
+;   extern char ch __attribute__((section("abc")));
+;   int test() {
+;     return global_func(0) + ch;
+;   }
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm test.c
+
+@ch = external dso_local local_unnamed_addr global i8, section "abc", align 1, !dbg !0
+
+; Function Attrs: nounwind
+define dso_local i32 @test() local_unnamed_addr #0 !dbg !16 {
+entry:
+  %call = tail call i32 @global_func(i8 signext 0) #2, !dbg !19
+  %0 = load i8, i8* @ch, align 1, !dbg !20, !tbaa !21
+  %conv = sext i8 %0 to i32, !dbg !20
+  %add = add nsw i32 %call, %conv, !dbg !24
+  ret i32 %add, !dbg !25
+}
+
+; 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   144
+; CHECK-NEXT:        .long   144
+; CHECK-NEXT:        .long   79
+; CHECK-NEXT:        .long   0                       # BTF_KIND_FUNC_PROTO(id = 1)
+; CHECK-NEXT:        .long   218103808               # 0xd000000
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   1                       # BTF_KIND_INT(id = 2)
+; CHECK-NEXT:        .long   16777216                # 0x1000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   16777248                # 0x1000020
+; CHECK-NEXT:        .long   5                       # BTF_KIND_FUNC(id = 3)
+; CHECK-NEXT:        .long   201326592               # 0xc000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   55                      # BTF_KIND_INT(id = 4)
+; CHECK-NEXT:        .long   16777216                # 0x1000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   16777224                # 0x1000008
+; CHECK-NEXT:        .long   60                      # BTF_KIND_VAR(id = 5)
+; CHECK-NEXT:        .long   234881024               # 0xe000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   0                       # BTF_KIND_FUNC_PROTO(id = 6)
+; CHECK-NEXT:        .long   218103809               # 0xd000001
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   0
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   63                      # BTF_KIND_VAR(id = 7)
+; CHECK-NEXT:        .long   234881024               # 0xe000000
+; CHECK-NEXT:        .long   6
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   75                      # BTF_KIND_DATASEC(id = 8)
+; CHECK-NEXT:        .long   251658242               # 0xf000002
+; CHECK-NEXT:        .long   0
+; CHECK-NEXT:        .long   5
+; CHECK-NEXT:        .long   ch
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   7
+; CHECK-NEXT:        .long   global_func
+; CHECK-NEXT:        .long   8
+; CHECK-NEXT:        .byte   0                       # string offset=0
+; CHECK-NEXT:        .ascii  "int"                   # string offset=1
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "test"                  # string offset=5
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  ".text"                 # string offset=10
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "/tmp/home/yhs/work/tests/extern/test.c" # string offset=16
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "char"                  # string offset=55
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "ch"                    # string offset=60
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "global_func"           # string offset=63
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "abc"                   # string offset=75
+; CHECK-NEXT:        .byte   0
+
+declare !dbg !6 dso_local i32 @global_func(i8 signext) local_unnamed_addr #1 section "abc"
+
+attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { nounwind }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!12, !13, !14}
+!llvm.ident = !{!15}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "ch", scope: !2, file: !3, line: 2, type: !10, isLocal: false, isDefinition: false)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 10.0.0 (https://github.com/llvm/llvm-project.git 0ad024346185b3f0b5167438e126568982b1168d)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, retainedTypes: !5, globals: !11, nameTableKind: None)
+!3 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/work/tests/extern")
+!4 = !{}
+!5 = !{!6}
+!6 = !DISubprogram(name: "global_func", scope: !3, file: !3, line: 1, type: !7, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !4)
+!7 = !DISubroutineType(types: !8)
+!8 = !{!9, !10}
+!9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!10 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
+!11 = !{!0}
+!12 = !{i32 2, !"Dwarf Version", i32 4}
+!13 = !{i32 2, !"Debug Info Version", i32 3}
+!14 = !{i32 1, !"wchar_size", i32 4}
+!15 = !{!"clang version 10.0.0 (https://github.com/llvm/llvm-project.git 0ad024346185b3f0b5167438e126568982b1168d)"}
+!16 = distinct !DISubprogram(name: "test", scope: !3, file: !3, line: 3, type: !17, scopeLine: 3, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !4)
+!17 = !DISubroutineType(types: !18)
+!18 = !{!9}
+!19 = !DILocation(line: 4, column: 10, scope: !16)
+!20 = !DILocation(line: 4, column: 27, scope: !16)
+!21 = !{!22, !22, i64 0}
+!22 = !{!"omnipotent char", !23, i64 0}
+!23 = !{!"Simple C/C++ TBAA"}
+!24 = !DILocation(line: 4, column: 25, scope: !16)
+!25 = !DILocation(line: 4, column: 3, scope: !16)

llvm/test/CodeGen/BPF/BTF/extern-var-struct-weak.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:
+;   typedef struct t1 { int f1; } __t1;
+;   extern __t1 global __attribute__((weak));
+;   int test() { return global.f1; }
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm test.c
+
+%struct.t1 = type { i32 }
+
+@global = extern_weak dso_local local_unnamed_addr global %struct.t1, align 4, !dbg !0
+; Function Attrs: norecurse nounwind readonly
+define dso_local i32 @test() local_unnamed_addr #0 !dbg !15 {
+entry:
+  %0 = load i32, i32* getelementptr (%struct.t1, %struct.t1* @global, i64 0, i32 0), align 4, !dbg !18, !tbaa !19
+  ret i32 %0, !dbg !24
+}
+
+; 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   92
+; CHECK-NEXT:        .long   92
+; CHECK-NEXT:        .long   73
+; CHECK-NEXT:        .long   0                       # BTF_KIND_FUNC_PROTO(id = 1)
+; CHECK-NEXT:        .long   218103808               # 0xd000000
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   1                       # BTF_KIND_INT(id = 2)
+; CHECK-NEXT:        .long   16777216                # 0x1000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   16777248                # 0x1000020
+; CHECK-NEXT:        .long   5                       # BTF_KIND_FUNC(id = 3)
+; CHECK-NEXT:        .long   201326592               # 0xc000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   55                      # BTF_KIND_TYPEDEF(id = 4)
+; CHECK-NEXT:        .long   134217728               # 0x8000000
+; CHECK-NEXT:        .long   5
+; CHECK-NEXT:        .long   60                      # BTF_KIND_STRUCT(id = 5)
+; CHECK-NEXT:        .long   67108865                # 0x4000001
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   63
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   0                       # 0x0
+; CHECK-NEXT:        .long   66                      # BTF_KIND_VAR(id = 6)
+; CHECK-NEXT:        .long   234881024               # 0xe000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .byte   0                       # string offset=0
+; CHECK-NEXT:        .ascii  "int"                   # string offset=1
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "test"                  # string offset=5
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  ".text"                 # string offset=10
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "/tmp/home/yhs/work/tests/extern/test.c" # string offset=16
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "__t1"                  # string offset=55
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "t1"                    # string offset=60
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "f1"                    # string offset=63
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "global"                # string offset=66
+; CHECK-NEXT:        .byte   0
+
+attributes #0 = { norecurse nounwind readonly "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!11, !12, !13}
+!llvm.ident = !{!14}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "global", scope: !2, file: !3, line: 2, type: !6, isLocal: false, isDefinition: false)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 10.0.0 (https://github.com/llvm/llvm-project.git 71a9518c93fe1dce9611c24bc707e5baf1f39f0d)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, nameTableKind: None)
+!3 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/work/tests/extern")
+!4 = !{}
+!5 = !{!0}
+!6 = !DIDerivedType(tag: DW_TAG_typedef, name: "__t1", file: !3, line: 1, baseType: !7)
+!7 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "t1", file: !3, line: 1, size: 32, elements: !8)
+!8 = !{!9}
+!9 = !DIDerivedType(tag: DW_TAG_member, name: "f1", scope: !7, file: !3, line: 1, baseType: !10, size: 32)
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{i32 7, !"Dwarf Version", i32 4}
+!12 = !{i32 2, !"Debug Info Version", i32 3}
+!13 = !{i32 1, !"wchar_size", i32 4}
+!14 = !{!"clang version 10.0.0 (https://github.com/llvm/llvm-project.git 71a9518c93fe1dce9611c24bc707e5baf1f39f0d)"}
+!15 = distinct !DISubprogram(name: "test", scope: !3, file: !3, line: 3, type: !16, scopeLine: 3, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !4)
+!16 = !DISubroutineType(types: !17)
+!17 = !{!10}
+!18 = !DILocation(line: 3, column: 28, scope: !15)
+!19 = !{!20, !21, i64 0}
+!20 = !{!"t1", !21, i64 0}
+!21 = !{!"int", !22, i64 0}
+!22 = !{!"omnipotent char", !23, i64 0}
+!23 = !{!"Simple C/C++ TBAA"}
+!24 = !DILocation(line: 3, column: 14, scope: !15)

llvm/test/CodeGen/BPF/BTF/extern-var-struct.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:
+;   typedef struct t1 { int f1; } __t1;
+;   extern __t1 global;
+;   int test() { return global.f1; }
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm test.c
+
+%struct.t1 = type { i32 }
+
+@global = external dso_local local_unnamed_addr global %struct.t1, align 4, !dbg !0
+
+; Function Attrs: norecurse nounwind readonly
+define dso_local i32 @test() local_unnamed_addr #0 !dbg !15 {
+entry:
+  %0 = load i32, i32* getelementptr inbounds (%struct.t1, %struct.t1* @global, i64 0, i32 0), align 4, !dbg !18, !tbaa !19
+  ret i32 %0, !dbg !24
+}
+
+; 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   92
+; CHECK-NEXT:        .long   92
+; CHECK-NEXT:        .long   73
+; CHECK-NEXT:        .long   0                       # BTF_KIND_FUNC_PROTO(id = 1)
+; CHECK-NEXT:        .long   218103808               # 0xd000000
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   1                       # BTF_KIND_INT(id = 2)
+; CHECK-NEXT:        .long   16777216                # 0x1000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   16777248                # 0x1000020
+; CHECK-NEXT:        .long   5                       # BTF_KIND_FUNC(id = 3)
+; CHECK-NEXT:        .long   201326592               # 0xc000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   55                      # BTF_KIND_TYPEDEF(id = 4)
+; CHECK-NEXT:        .long   134217728               # 0x8000000
+; CHECK-NEXT:        .long   5
+; CHECK-NEXT:        .long   60                      # BTF_KIND_STRUCT(id = 5)
+; CHECK-NEXT:        .long   67108865                # 0x4000001
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   63
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   0                       # 0x0
+; CHECK-NEXT:        .long   66                      # BTF_KIND_VAR(id = 6)
+; CHECK-NEXT:        .long   234881024               # 0xe000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .byte   0                       # string offset=0
+; CHECK-NEXT:        .ascii  "int"                   # string offset=1
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "test"                  # string offset=5
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  ".text"                 # string offset=10
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "/tmp/home/yhs/work/tests/extern/test.c" # string offset=16
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "__t1"                  # string offset=55
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "t1"                    # string offset=60
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "f1"                    # string offset=63
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "global"                # string offset=66
+; CHECK-NEXT:        .byte   0
+
+attributes #0 = { norecurse nounwind readonly "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!11, !12, !13}
+!llvm.ident = !{!14}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "global", scope: !2, file: !3, line: 2, type: !6, isLocal: false, isDefinition: false)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 10.0.0 (https://github.com/llvm/llvm-project.git 2798d63180f4cc873bdaf689705fd4f9521ae89f)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, nameTableKind: None)
+!3 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/work/tests/extern")
+!4 = !{}
+!5 = !{!0}
+!6 = !DIDerivedType(tag: DW_TAG_typedef, name: "__t1", file: !3, line: 1, baseType: !7)
+!7 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "t1", file: !3, line: 1, size: 32, elements: !8)
+!8 = !{!9}
+!9 = !DIDerivedType(tag: DW_TAG_member, name: "f1", scope: !7, file: !3, line: 1, baseType: !10, size: 32)
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{i32 2, !"Dwarf Version", i32 4}
+!12 = !{i32 2, !"Debug Info Version", i32 3}
+!13 = !{i32 1, !"wchar_size", i32 4}
+!14 = !{!"clang version 10.0.0 (https://github.com/llvm/llvm-project.git 2798d63180f4cc873bdaf689705fd4f9521ae89f)"}
+!15 = distinct !DISubprogram(name: "test", scope: !3, file: !3, line: 4, type: !16, scopeLine: 4, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !4)
+!16 = !DISubroutineType(types: !17)
+!17 = !{!10}
+!18 = !DILocation(line: 4, column: 28, scope: !15)
+!19 = !{!20, !21, i64 0}
+!20 = !{!"t1", !21, i64 0}
+!21 = !{!"int", !22, i64 0}
+!22 = !{!"omnipotent char", !23, i64 0}
+!23 = !{!"Simple C/C++ TBAA"}
+!24 = !DILocation(line: 4, column: 14, scope: !15)

llvm/test/CodeGen/BPF/BTF/extern-var-weak-section.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:
+;   extern int global_func(char c) __attribute__((weak, section("abc")));
+;   extern char ch __attribute__((weak, section("abc")));
+;   int test() {
+;     return global_func(0) + ch;
+;   }
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm test.c
+
+@ch = extern_weak dso_local local_unnamed_addr global i8, section "abc", align 1, !dbg !0
+; Function Attrs: nounwind
+define dso_local i32 @test() local_unnamed_addr #0 !dbg !16 {
+entry:
+  %call = tail call i32 @global_func(i8 signext 0) #2, !dbg !19
+  %0 = load i8, i8* @ch, align 1, !dbg !20, !tbaa !21
+  %conv = sext i8 %0 to i32, !dbg !20
+  %add = add nsw i32 %call, %conv, !dbg !24
+  ret i32 %add, !dbg !25
+}
+declare !dbg !6 extern_weak dso_local i32 @global_func(i8 signext) local_unnamed_addr #1 section "abc"
+
+; 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   144
+; CHECK-NEXT:        .long   144
+; CHECK-NEXT:        .long   79
+; CHECK-NEXT:        .long   0                       # BTF_KIND_FUNC_PROTO(id = 1)
+; CHECK-NEXT:        .long   218103808               # 0xd000000
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   1                       # BTF_KIND_INT(id = 2)
+; CHECK-NEXT:        .long   16777216                # 0x1000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   16777248                # 0x1000020
+; CHECK-NEXT:        .long   5                       # BTF_KIND_FUNC(id = 3)
+; CHECK-NEXT:        .long   201326592               # 0xc000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   55                      # BTF_KIND_INT(id = 4)
+; CHECK-NEXT:        .long   16777216                # 0x1000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   16777224                # 0x1000008
+; CHECK-NEXT:        .long   60                      # BTF_KIND_VAR(id = 5)
+; CHECK-NEXT:        .long   234881024               # 0xe000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   0                       # BTF_KIND_FUNC_PROTO(id = 6)
+; CHECK-NEXT:        .long   218103809               # 0xd000001
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   0
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   63                      # BTF_KIND_VAR(id = 7)
+; CHECK-NEXT:        .long   234881024               # 0xe000000
+; CHECK-NEXT:        .long   6
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   75                      # BTF_KIND_DATASEC(id = 8)
+; CHECK-NEXT:        .long   251658242               # 0xf000002
+; CHECK-NEXT:        .long   0
+; CHECK-NEXT:        .long   5
+; CHECK-NEXT:        .long   ch
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   7
+; CHECK-NEXT:        .long   global_func
+; CHECK-NEXT:        .long   8
+; CHECK-NEXT:        .byte   0                       # string offset=0
+; CHECK-NEXT:        .ascii  "int"                   # string offset=1
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "test"                  # string offset=5
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  ".text"                 # string offset=10
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "/tmp/home/yhs/work/tests/extern/test.c" # string offset=16
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "char"                  # string offset=55
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "ch"                    # string offset=60
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "global_func"           # string offset=63
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "abc"                   # string offset=75
+; CHECK-NEXT:        .byte   0
+
+attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { nounwind }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!12, !13, !14}
+!llvm.ident = !{!15}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "ch", scope: !2, file: !3, line: 2, type: !10, isLocal: false, isDefinition: false)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 10.0.0 (https://github.com/llvm/llvm-project.git 71a9518c93fe1dce9611c24bc707e5baf1f39f0d)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, retainedTypes: !5, globals: !11, nameTableKind: None)
+!3 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/work/tests/extern")
+!4 = !{}
+!5 = !{!6}
+!6 = !DISubprogram(name: "global_func", scope: !3, file: !3, line: 1, type: !7, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !4)
+!7 = !DISubroutineType(types: !8)
+!8 = !{!9, !10}
+!9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!10 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
+!11 = !{!0}
+!12 = !{i32 7, !"Dwarf Version", i32 4}
+!13 = !{i32 2, !"Debug Info Version", i32 3}
+!14 = !{i32 1, !"wchar_size", i32 4}
+!15 = !{!"clang version 10.0.0 (https://github.com/llvm/llvm-project.git 71a9518c93fe1dce9611c24bc707e5baf1f39f0d)"}
+!16 = distinct !DISubprogram(name: "test", scope: !3, file: !3, line: 3, type: !17, scopeLine: 3, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !4)
+!17 = !DISubroutineType(types: !18)
+!18 = !{!9}
+!19 = !DILocation(line: 4, column: 10, scope: !16)
+!20 = !DILocation(line: 4, column: 27, scope: !16)
+!21 = !{!22, !22, i64 0}
+!22 = !{!"omnipotent char", !23, i64 0}
+!23 = !{!"Simple C/C++ TBAA"}
+!24 = !DILocation(line: 4, column: 25, scope: !16)
+!25 = !DILocation(line: 4, column: 3, scope: !16)