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BPF: generate proper BTF for globals with WeakODRLinkage
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For a global weak symbol defined as below:
  char g __attribute__((weak)) = 2;
LLVM generates an allocated global with WeakAnyLinkage,
for which BPF backend generates proper BTF info.

For the above example, if a modifier "const" is added like
  const char g __attribute__((weak)) = 2;
LLVM generates an allocated global with WeakODRLinkage,
for which BPF backend didn't generate any BTF as it
didn't handle WeakODRLinkage.

This patch addes support for WeakODRLinkage and proper
BTF info can be generated for weak symbol defined with
"const" modifier.

Differential Revision: https://reviews.llvm.org/D100362
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@yonghong-song
yonghong-song committed Apr 13, 2021
1 parent b5b2c81 commit 968292c
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1 change: 1 addition & 0 deletions llvm/lib/Target/BPF/BTFDebug.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1196,6 +1196,7 @@ void BTFDebug::processGlobals(bool ProcessingMapDef) {
if (Linkage != GlobalValue::InternalLinkage &&
Linkage != GlobalValue::ExternalLinkage &&
Linkage != GlobalValue::WeakAnyLinkage &&
Linkage != GlobalValue::WeakODRLinkage &&
Linkage != GlobalValue::ExternalWeakLinkage)
continue;

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86 changes: 86 additions & 0 deletions llvm/test/CodeGen/BPF/BTF/weak-global-3.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,86 @@
; 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:
; const volatile char g __attribute__((weak)) = 2;
; int test() {
; return g;
; }
; Compilation flag:
; clang -target bpf -O2 -g -S -emit-llvm test.c

@g = weak_odr dso_local constant i8 2, align 1, !dbg !0

; Function Attrs: nofree norecurse nounwind willreturn
define dso_local i32 @test() local_unnamed_addr #0 !dbg !13 {
entry:
%0 = load volatile i8, i8* @g, align 1, !dbg !17, !tbaa !18
%conv = sext i8 %0 to i32, !dbg !17
ret i32 %conv, !dbg !21
}

; CHECK: .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 201326593 # 0xc000001
; CHECK-NEXT: .long 1
; CHECK-NEXT: .long 0 # BTF_KIND_CONST(id = 4)
; CHECK-NEXT: .long 167772160 # 0xa000000
; CHECK-NEXT: .long 5
; CHECK-NEXT: .long 0 # BTF_KIND_VOLATILE(id = 5)
; CHECK-NEXT: .long 150994944 # 0x9000000
; CHECK-NEXT: .long 6
; CHECK-NEXT: .long 47 # BTF_KIND_INT(id = 6)
; CHECK-NEXT: .long 16777216 # 0x1000000
; CHECK-NEXT: .long 1
; CHECK-NEXT: .long 16777224 # 0x1000008
; CHECK-NEXT: .long 52 # BTF_KIND_VAR(id = 7)
; CHECK-NEXT: .long 234881024 # 0xe000000
; CHECK-NEXT: .long 4
; CHECK-NEXT: .long 1
; CHECK-NEXT: .long 54 # BTF_KIND_DATASEC(id = 8)
; CHECK-NEXT: .long 251658241 # 0xf000001
; CHECK-NEXT: .long 0
; CHECK-NEXT: .long 7
; CHECK-NEXT: .long g
; CHECK-NEXT: .long 1

; CHECK: .ascii "int" # string offset=1
; CHECK: .ascii "test" # string offset=5
; CHECK: .ascii "char" # string offset=47
; CHECK: .byte 103 # string offset=52
; CHECK: .ascii ".rodata" # string offset=54

attributes #0 = { nofree norecurse nounwind willreturn "frame-pointer"="all" "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }

!llvm.dbg.cu = !{!2}
!llvm.module.flags = !{!9, !10, !11}
!llvm.ident = !{!12}

!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
!1 = distinct !DIGlobalVariable(name: "g", scope: !2, file: !3, line: 1, type: !6, isLocal: false, isDefinition: true)
!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 13.0.0 (https://github.com/llvm/llvm-project.git 9cc417cbca1cece0d55fa3d1e15682943a06139e)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, splitDebugInlining: false, nameTableKind: None)
!3 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/btf/tests")
!4 = !{}
!5 = !{!0}
!6 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !7)
!7 = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: !8)
!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 13.0.0 (https://github.com/llvm/llvm-project.git 9cc417cbca1cece0d55fa3d1e15682943a06139e)"}
!13 = distinct !DISubprogram(name: "test", scope: !3, file: !3, line: 2, type: !14, scopeLine: 2, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !4)
!14 = !DISubroutineType(types: !15)
!15 = !{!16}
!16 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!17 = !DILocation(line: 3, column: 10, scope: !13)
!18 = !{!19, !19, i64 0}
!19 = !{!"omnipotent char", !20, i64 0}
!20 = !{!"Simple C/C++ TBAA"}
!21 = !DILocation(line: 3, column: 3, scope: !13)

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