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Go1.25 リリースパーティ ~ nil pointer bug ~
09/30/2025
sivchari
newmo Inc
The Go gopher was designed by Renée French.
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自己紹介
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● sivchari
○ X/GitHub @sivchari
● newmo
● Kubernetes maintainer
○ Cluster API
○ Kube API Linter
● Go Conference メインオーガナイザー
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Go1.25からのCompiler
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{
Go1.25のCompiler
●
nil pointer bug
●
DWARF5 support
●
Faster slices
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{
Go1.25のCompiler
●
nil pointer bug
●
DWARF5 support
●
Faster slices
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nil pointer bug
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nil pointer bug
m := map[string]*struct {
field int
}{}
v, ok := m[“key”]
valid := v.field >= 0 // 1
if !ok {
println(“mark”)
return
}
println(valid) // 2
Go N <= 1.24
panic or not?
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nil pointer bug
m := map[string]*struct {
field int
}{}
v, ok := m[“key”]
valid := v.field >= 0 // 1
if !ok {
println(“mark”)
return
}
println(valid) // 2
Go N <= 1.24
panic or not?
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nil pointer bug
m := map[string]*struct {
field int
}{}
v, ok := m[“key”]
valid := v.field >= 0 // 1
if !ok {
println(“mark”)
return
}
println(valid) // 2
Go N >= 1.24
panic or not?
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nil pointer bug
m := map[string]*struct {
field int
}{}
v, ok := m[“key”]
valid := v.field >= 0 // 1
if !ok {
println(“mark”)
return
}
println(valid) // 2
Go N >= 1.24
panic or not?
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CompilerとMemory Model
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CompilerとMemory Model
● Issue #72860
○ Go1.21で行ったコンパイラ最適化が問題
○ Compilerが遅延評価していた
○ compiler/ssa/internal/tighten.go
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CompilerとMemory Model
● GoのMemory Modelに違反する
Requirement 1: The memory operations in each goroutine must correspond to a
correct sequential execution of that goroutine, given the values read from and
written to memory. That execution must be consistent with the sequenced before
relation, defined as the partial order requirements set out by the Go language
specification for Go's control flow constructs as well as the order of evaluation for
expressions.
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CompilerとMemory Model
● Memory Modelとの不一致
○ 最適化がされても実行順序は維持されている
必要がある(Sequenced before)
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CompilerとMemory Model
m := map[string]*struct {
field int
}{}
v, ok := m[“key”]
valid := v.field >= 0 // 1
if !ok {
println(“mark”)
return
}
println(valid) // 2
valid
is
sequenced
before
`if !ok`
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CompilerとMemory Model
m := map[string]*struct {
field int
}{}
v, ok := m[“key”]
if !ok {
println(“mark”)
return
}
valid := v.field >= 0 // 1
println(valid) // 2
valid
is
sequenced
before
`if !ok`
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CompilerとMemory Model
if opcodeTable[v.Op].nilCheck {
// Nil checks need to stay in
their block. See issue 72860.
continue
}
CL 657715
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CompilerとMemory Model
b4: ← b2
LoweredNilCheck v44 v40
GOSSAFUNC=main GOTOOLCHAIN=go1.24.0 go build main.go
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CompilerとMemory Model
b2:
LoweredNilCheck v44 v40
GOSSAFUNC=main GOTOOLCHAIN=go1.25.0 go build main.go
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まとめ
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● Go1.25からコンパイラ最適化が修正された
● Goとしてのバグである
● リンター作成してみると面白いかも