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dvyukov opened this issue Nov 16, 2015 · 4 comments
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cmd/compile: nil pointer defer in outervalue #13265

dvyukov opened this issue Nov 16, 2015 · 4 comments
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FrozenDueToAge RaceDetector
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@dvyukov
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dvyukov commented Nov 16, 2015

Reproducer:
https://gist.githubusercontent.com/dvyukov/20774908b7ea4e70a16d/raw/b0df0a7818189971dd47daa7d93fdc5b215decf4/test.go

$ go build -race gogo.go

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x78 pc=0x653771]

goroutine 1 [running]:
cmd/compile/internal/gc.outervalue(0x0, 0xc82034bd80)
    src/cmd/compile/internal/gc/walk.go:2345 +0x21
cmd/compile/internal/gc.iscallret(0x0, 0xc820359ef0)
    src/cmd/compile/internal/gc/walk.go:2034 +0x21
cmd/compile/internal/gc.instrumentnode(0xc8203e1518, 0xc8203e1520, 0x0, 0x0)
    src/cmd/compile/internal/gc/racewalk.go:161 +0x14f1
cmd/compile/internal/gc.instrumentnode(0xc8201e9cb8, 0xc820355060, 0x0, 0x0)
    src/cmd/compile/internal/gc/racewalk.go:128 +0x15f
cmd/compile/internal/gc.instrumentnode(0xc82034a9e0, 0xc8203e1680, 0x0, 0x0)
    src/cmd/compile/internal/gc/racewalk.go:385 +0x1796
cmd/compile/internal/gc.instrumentlist(0xc82034a9e0, 0x0)
    src/cmd/compile/internal/gc/racewalk.go:94 +0x6e
cmd/compile/internal/gc.instrument(0xc8201e5830)
    src/cmd/compile/internal/gc/racewalk.go:58 +0x829
cmd/compile/internal/gc.compile(0xc8201e5830)
    src/cmd/compile/internal/gc/pgen.go:403 +0x5d4
cmd/compile/internal/gc.funccompile(0xc8201e5830)
    src/cmd/compile/internal/gc/dcl.go:1448 +0x1c0
cmd/compile/internal/gc.Main()
    src/cmd/compile/internal/gc/lex.go:487 +0x2150
cmd/compile/internal/amd64.Main()
    src/cmd/compile/internal/amd64/galign.go:127 +0x58d
main.main()
    src/cmd/compile/main.go:27 +0x36f

go version devel +25a28da Sun Nov 15 23:41:28 2015 +0000 linux/amd64
@dvyukov
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dvyukov commented Nov 16, 2015

@rsc @griesemer

@ianlancetaylor ianlancetaylor added this to the Go1.6 milestone Nov 16, 2015
@griesemer
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This is unrelated to the new parser code. The bug also appears with:
go build -gcflags=-oldparser -race foo.go

@rsc rsc modified the milestones: Unplanned, Go1.6 Dec 5, 2015
@gopherbot
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CL https://golang.org/cl/34929 mentions this issue.

@JayNakrani
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JayNakrani commented Jan 8, 2017 •
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ls[i].Right is nil at line #157. That's causing iscallret() to pass nil to outervalue().

From what I understand, instrumentnode() is trying to determine whether an OAS node after function call was copying results off stack. But it appears from the dump (obtained with JayNakrani@c5f8b0b), that there can be autotmp OAS nodes with Right set to nil just after CALLFUNC. If it's okay for an OAS node to have nil Right, then fix is simple: golang.org/cl/34929

I also tried to isolate the problem in the source code, and it's the for loop's third assignment in main(). i.e the following snippet,

for ; false; Var1, Var342, (*(((<-Var343)[(<-((*(Var393))[(((make([][0]int, 0, 1))[(*(*(([]**int{})[(*((Var406)[Var476]))-(1)])))+(1)])[(<-make(chan int, 1))])+(1)])[(*(([]*int{})[(<-make(chan int))]))+(1)])])[(int)((Var667)[((func(chan string, uint) int)(nil))(make(chan string), uint(1))])])) = false, ((func(bool, int, rune, int16) (chan complex128, chan complex64, []int))(nil)), (*[]interface{})(nil) {
}

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@rsc @dvyukov @ianlancetaylor @JayNakrani @griesemer @gopherbot