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Differential D100392

BPF: remove default .extern data section
ClosedPublic

Authored by yonghong-song on Apr 13 2021, 9:30 AM.

Details

Reviewers
ast
anakryiko
Commits
rGa285bdb56fb4: BPF: remove default .extern data section
Summary

Currently, for any extern variable, if it doesn't have
section attribution, it will be put into a default ".extern"
btf DataSec. The initial design is to put every extern
variable in a DataSec so libbpf can use it.

But later on, libbpf actually requires extern variables
to put into special sections, e.g., ".kconfig", ".ksyms", etc.
so they can be used properly based on section name.

Andrii mentioned since ".extern" variables are
not actually used, it makes sense to remove it from
the compiler so libbpf does not need to deal with it,
esp. for static linking. The BTF for these extern variables
is still generated.

With this patch, I tested kernel selftests/bpf and all tests
passed. Indeed, removing ".extern" DataSec seems having no
impact.

Diff Detail

Event Timeline

yonghong-song created this revision.Apr 13 2021, 9:30 AM
Herald added a subscriber: hiraditya. · View Herald TranscriptApr 13 2021, 9:30 AM
yonghong-song requested review of this revision.Apr 13 2021, 9:30 AM
Herald added a project: Restricted Project. · View Herald TranscriptApr 13 2021, 9:30 AM
Herald added a subscriber: llvm-commits. · View Herald Transcript
Harbormaster completed remote builds in B98506: Diff 337187.Apr 13 2021, 9:31 AM
ast accepted this revision.Apr 13 2021, 9:54 AM
This revision is now accepted and ready to land.Apr 13 2021, 9:54 AM
anakryiko accepted this revision.Apr 13 2021, 10:36 AM

LGTM, thanks!

This revision was landed with ongoing or failed builds.Apr 13 2021, 11:38 AM
Closed by commit rGa285bdb56fb4: BPF: remove default .extern data section (authored by yonghong-song). · Explain Why
This revision was automatically updated to reflect the committed changes.
yonghong-song added a commit: rGa285bdb56fb4: BPF: remove default .extern data section.

Revision Contents

PathSize
llvm/
lib/
Target/
BPF/
8 lines
test/
CodeGen/
BPF/
BTF/
14 lines
14 lines

Diff 337218

llvm/lib/Target/BPF/BTFDebug.cpp

Show First 20 Lines • Show All 1,140 Lines • ▼ Show 20 Lines for (const GlobalVariable &Global : M->globals()) {
if (Global.hasSection()) { if (Global.hasSection()) {
SecName = Global.getSection(); SecName = Global.getSection();
} else if (Global.hasInitializer()) { } else if (Global.hasInitializer()) {
// data, bss, or readonly sections // data, bss, or readonly sections
if (Global.isConstant()) if (Global.isConstant())
SecName = ".rodata"; SecName = ".rodata";
else else
SecName = Global.getInitializer()->isZeroValue() ? ".bss" : ".data"; SecName = Global.getInitializer()->isZeroValue() ? ".bss" : ".data";
} else {
// extern variables without explicit section,
// put them into ".extern" section.
SecName = ".extern";
} }
if (ProcessingMapDef != SecName.startswith(".maps")) if (ProcessingMapDef != SecName.startswith(".maps"))
continue; continue;
// Create a .rodata datasec if the global variable is an initialized // Create a .rodata datasec if the global variable is an initialized
// constant with private linkage and if it won't be in .rodata.str<#> // constant with private linkage and if it won't be in .rodata.str<#>
// and .rodata.cst<#> sections. // and .rodata.cst<#> sections.
▲ Show 20 Lines • Show All 47 Lines • ▼ Show 20 Lines for (const GlobalVariable &Global : M->globals()) {
} else { } else {
GVarInfo = BTF::VAR_GLOBAL_EXTERNAL; GVarInfo = BTF::VAR_GLOBAL_EXTERNAL;
} }
auto VarEntry = auto VarEntry =
std::make_unique<BTFKindVar>(Global.getName(), GVTypeId, GVarInfo); std::make_unique<BTFKindVar>(Global.getName(), GVTypeId, GVarInfo);
uint32_t VarId = addType(std::move(VarEntry)); uint32_t VarId = addType(std::move(VarEntry));
assert(!SecName.empty()); // An empty SecName means an extern variable without section attribute.
if (SecName.empty())
continue;
// Find or create a DataSec // Find or create a DataSec
if (DataSecEntries.find(std::string(SecName)) == DataSecEntries.end()) { if (DataSecEntries.find(std::string(SecName)) == DataSecEntries.end()) {
DataSecEntries[std::string(SecName)] = DataSecEntries[std::string(SecName)] =
std::make_unique<BTFKindDataSec>(Asm, std::string(SecName)); std::make_unique<BTFKindDataSec>(Asm, std::string(SecName));
} }
// Calculate symbol size // Calculate symbol size
▲ Show 20 Lines • Show All 142 Lines • Show Last 20 Lines

llvm/test/CodeGen/BPF/BTF/extern-var-struct-weak.ll

Show All 18 Lines
} }
; CHECK: .section .BTF,"",@progbits ; CHECK: .section .BTF,"",@progbits
; CHECK-NEXT: .short 60319 # 0xeb9f ; CHECK-NEXT: .short 60319 # 0xeb9f
; CHECK-NEXT: .byte 1 ; CHECK-NEXT: .byte 1
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .long 24 ; CHECK-NEXT: .long 24
; CHECK-NEXT: .long 0 ; CHECK-NEXT: .long 0
; CHECK-NEXT: .long 116 ; CHECK-NEXT: .long 92
; CHECK-NEXT: .long 116 ; CHECK-NEXT: .long 92
; CHECK-NEXT: .long 81 ; CHECK-NEXT: .long 73
; CHECK-NEXT: .long 0 # BTF_KIND_FUNC_PROTO(id = 1) ; CHECK-NEXT: .long 0 # BTF_KIND_FUNC_PROTO(id = 1)
; CHECK-NEXT: .long 218103808 # 0xd000000 ; CHECK-NEXT: .long 218103808 # 0xd000000
; CHECK-NEXT: .long 2 ; CHECK-NEXT: .long 2
; CHECK-NEXT: .long 1 # BTF_KIND_INT(id = 2) ; CHECK-NEXT: .long 1 # BTF_KIND_INT(id = 2)
; CHECK-NEXT: .long 16777216 # 0x1000000 ; CHECK-NEXT: .long 16777216 # 0x1000000
; CHECK-NEXT: .long 4 ; CHECK-NEXT: .long 4
; CHECK-NEXT: .long 16777248 # 0x1000020 ; CHECK-NEXT: .long 16777248 # 0x1000020
; CHECK-NEXT: .long 5 # BTF_KIND_FUNC(id = 3) ; CHECK-NEXT: .long 5 # BTF_KIND_FUNC(id = 3)
; CHECK-NEXT: .long 201326593 # 0xc000001 ; CHECK-NEXT: .long 201326593 # 0xc000001
; CHECK-NEXT: .long 1 ; CHECK-NEXT: .long 1
; CHECK-NEXT: .long 55 # BTF_KIND_TYPEDEF(id = 4) ; CHECK-NEXT: .long 55 # BTF_KIND_TYPEDEF(id = 4)
; CHECK-NEXT: .long 134217728 # 0x8000000 ; CHECK-NEXT: .long 134217728 # 0x8000000
; CHECK-NEXT: .long 5 ; CHECK-NEXT: .long 5
; CHECK-NEXT: .long 60 # BTF_KIND_STRUCT(id = 5) ; CHECK-NEXT: .long 60 # BTF_KIND_STRUCT(id = 5)
; CHECK-NEXT: .long 67108865 # 0x4000001 ; CHECK-NEXT: .long 67108865 # 0x4000001
; CHECK-NEXT: .long 4 ; CHECK-NEXT: .long 4
; CHECK-NEXT: .long 63 ; CHECK-NEXT: .long 63
; CHECK-NEXT: .long 2 ; CHECK-NEXT: .long 2
; CHECK-NEXT: .long 0 # 0x0 ; CHECK-NEXT: .long 0 # 0x0
; CHECK-NEXT: .long 66 # BTF_KIND_VAR(id = 6) ; CHECK-NEXT: .long 66 # BTF_KIND_VAR(id = 6)
; CHECK-NEXT: .long 234881024 # 0xe000000 ; CHECK-NEXT: .long 234881024 # 0xe000000
; CHECK-NEXT: .long 4 ; CHECK-NEXT: .long 4
; CHECK-NEXT: .long 2 ; CHECK-NEXT: .long 2
; CHECK-NEXT: .long 73 # BTF_KIND_DATASEC(id = 7)
; CHECK-NEXT: .long 251658241 # 0xf000001
; CHECK-NEXT: .long 0
; CHECK-NEXT: .long 6
; CHECK-NEXT: .long global
; CHECK-NEXT: .long 4
; CHECK-NEXT: .byte 0 # string offset=0 ; CHECK-NEXT: .byte 0 # string offset=0
; CHECK-NEXT: .ascii "int" # string offset=1 ; CHECK-NEXT: .ascii "int" # string offset=1
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "test" # string offset=5 ; CHECK-NEXT: .ascii "test" # string offset=5
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii ".text" # string offset=10 ; CHECK-NEXT: .ascii ".text" # string offset=10
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "/tmp/home/yhs/work/tests/extern/test.c" # string offset=16 ; CHECK-NEXT: .ascii "/tmp/home/yhs/work/tests/extern/test.c" # string offset=16
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "__t1" # string offset=55 ; CHECK-NEXT: .ascii "__t1" # string offset=55
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "t1" # string offset=60 ; CHECK-NEXT: .ascii "t1" # string offset=60
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "f1" # string offset=63 ; CHECK-NEXT: .ascii "f1" # string offset=63
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "global" # string offset=66 ; CHECK-NEXT: .ascii "global" # string offset=66
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii ".extern" # string offset=73
; 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" } 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.dbg.cu = !{!2}
!llvm.module.flags = !{!11, !12, !13} !llvm.module.flags = !{!11, !12, !13}
!llvm.ident = !{!14} !llvm.ident = !{!14}
!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression()) !0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
Show All 24 Lines

llvm/test/CodeGen/BPF/BTF/extern-var-struct.ll

Show All 19 Lines
} }
; CHECK: .section .BTF,"",@progbits ; CHECK: .section .BTF,"",@progbits
; CHECK-NEXT: .short 60319 # 0xeb9f ; CHECK-NEXT: .short 60319 # 0xeb9f
; CHECK-NEXT: .byte 1 ; CHECK-NEXT: .byte 1
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .long 24 ; CHECK-NEXT: .long 24
; CHECK-NEXT: .long 0 ; CHECK-NEXT: .long 0
; CHECK-NEXT: .long 116 ; CHECK-NEXT: .long 92
; CHECK-NEXT: .long 116 ; CHECK-NEXT: .long 92
; CHECK-NEXT: .long 81 ; CHECK-NEXT: .long 73
; CHECK-NEXT: .long 0 # BTF_KIND_FUNC_PROTO(id = 1) ; CHECK-NEXT: .long 0 # BTF_KIND_FUNC_PROTO(id = 1)
; CHECK-NEXT: .long 218103808 # 0xd000000 ; CHECK-NEXT: .long 218103808 # 0xd000000
; CHECK-NEXT: .long 2 ; CHECK-NEXT: .long 2
; CHECK-NEXT: .long 1 # BTF_KIND_INT(id = 2) ; CHECK-NEXT: .long 1 # BTF_KIND_INT(id = 2)
; CHECK-NEXT: .long 16777216 # 0x1000000 ; CHECK-NEXT: .long 16777216 # 0x1000000
; CHECK-NEXT: .long 4 ; CHECK-NEXT: .long 4
; CHECK-NEXT: .long 16777248 # 0x1000020 ; CHECK-NEXT: .long 16777248 # 0x1000020
; CHECK-NEXT: .long 5 # BTF_KIND_FUNC(id = 3) ; CHECK-NEXT: .long 5 # BTF_KIND_FUNC(id = 3)
; CHECK-NEXT: .long 201326593 # 0xc000001 ; CHECK-NEXT: .long 201326593 # 0xc000001
; CHECK-NEXT: .long 1 ; CHECK-NEXT: .long 1
; CHECK-NEXT: .long 55 # BTF_KIND_TYPEDEF(id = 4) ; CHECK-NEXT: .long 55 # BTF_KIND_TYPEDEF(id = 4)
; CHECK-NEXT: .long 134217728 # 0x8000000 ; CHECK-NEXT: .long 134217728 # 0x8000000
; CHECK-NEXT: .long 5 ; CHECK-NEXT: .long 5
; CHECK-NEXT: .long 60 # BTF_KIND_STRUCT(id = 5) ; CHECK-NEXT: .long 60 # BTF_KIND_STRUCT(id = 5)
; CHECK-NEXT: .long 67108865 # 0x4000001 ; CHECK-NEXT: .long 67108865 # 0x4000001
; CHECK-NEXT: .long 4 ; CHECK-NEXT: .long 4
; CHECK-NEXT: .long 63 ; CHECK-NEXT: .long 63
; CHECK-NEXT: .long 2 ; CHECK-NEXT: .long 2
; CHECK-NEXT: .long 0 # 0x0 ; CHECK-NEXT: .long 0 # 0x0
; CHECK-NEXT: .long 66 # BTF_KIND_VAR(id = 6) ; CHECK-NEXT: .long 66 # BTF_KIND_VAR(id = 6)
; CHECK-NEXT: .long 234881024 # 0xe000000 ; CHECK-NEXT: .long 234881024 # 0xe000000
; CHECK-NEXT: .long 4 ; CHECK-NEXT: .long 4
; CHECK-NEXT: .long 2 ; CHECK-NEXT: .long 2
; CHECK-NEXT: .long 73 # BTF_KIND_DATASEC(id = 7)
; CHECK-NEXT: .long 251658241 # 0xf000001
; CHECK-NEXT: .long 0
; CHECK-NEXT: .long 6
; CHECK-NEXT: .long global
; CHECK-NEXT: .long 4
; CHECK-NEXT: .byte 0 # string offset=0 ; CHECK-NEXT: .byte 0 # string offset=0
; CHECK-NEXT: .ascii "int" # string offset=1 ; CHECK-NEXT: .ascii "int" # string offset=1
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "test" # string offset=5 ; CHECK-NEXT: .ascii "test" # string offset=5
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii ".text" # string offset=10 ; CHECK-NEXT: .ascii ".text" # string offset=10
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "/tmp/home/yhs/work/tests/extern/test.c" # string offset=16 ; CHECK-NEXT: .ascii "/tmp/home/yhs/work/tests/extern/test.c" # string offset=16
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "__t1" # string offset=55 ; CHECK-NEXT: .ascii "__t1" # string offset=55
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "t1" # string offset=60 ; CHECK-NEXT: .ascii "t1" # string offset=60
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "f1" # string offset=63 ; CHECK-NEXT: .ascii "f1" # string offset=63
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "global" # string offset=66 ; CHECK-NEXT: .ascii "global" # string offset=66
; CHECK-NEXT: .byte 0 ; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii ".extern" # string offset=73
; 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" } 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.dbg.cu = !{!2}
!llvm.module.flags = !{!11, !12, !13} !llvm.module.flags = !{!11, !12, !13}
!llvm.ident = !{!14} !llvm.ident = !{!14}
!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression()) !0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
Show All 24 Lines