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SIGSEGV from fmt.Printf() when using go/ast.Inspect() #28729

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entrope opened this issue Nov 12, 2018 · 3 comments
Closed

SIGSEGV from fmt.Printf() when using go/ast.Inspect() #28729

entrope opened this issue Nov 12, 2018 · 3 comments

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@entrope
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@entrope entrope commented Nov 12, 2018

What version of Go are you using (go version)?

$ go version
go version go1.10.4 linux/amd64

Does this issue reproduce with the latest release?

Yes, similar SIGSEGV with go version devel +f58b02a29c Sun Nov 11 18:49:40 2018 +0000 linux/amd64, go version go1.11.2 linux/amd64, and go version go1.10.5 linux/amd64. (The last two fail unit tests on my Ubuntu 18.04 system, issue #28499.)

What operating system and processor architecture are you using (go env)?

go env Output
$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/mdpoole/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/mdpoole/go"
GORACE=""
GOROOT="/usr/lib/go-1.10"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go-1.10/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build101601023=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I ran the code at https://play.golang.org/p/KIUY0ozcK_8 .

What did you expect to see?

The program should terminate normally.

What did you see instead?

*ast.GenDecl at 15..32: &{ 15 import 22 [0x442300] 31}
*ast.ImportSpec at 25..30: &{  0x40c0f0  0}
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0xffffffff addr=0x0 pc=0x112fa2]

goroutine 1 [running]:
main.main.func1(0x0, 0x0, 0x1785b0, 0x13f6c0)
	/tmp/sandbox244933151/main.go:25 +0x22
go/ast.inspector.Visit(0x167530, 0x0, 0x0, 0x442300, 0x1785b0, 0x442300)
	/usr/local/go/src/go/ast/walk.go:373 +0x40
go/ast.Walk(0x1780f0, 0x167530, 0x178530, 0x442320)
	/usr/local/go/src/go/ast/walk.go:367 +0x1a0
go/ast.Inspect(0x178530, 0x442320, 0x167530, 0x1317a0)
	/usr/local/go/src/go/ast/walk.go:385 +0x40
main.main()
	/tmp/sandbox244933151/main.go:22 +0x120

Program exited: status 2.
@entrope

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@entrope entrope commented Nov 12, 2018

After a bit more poking, the problem is that the visitor function is being passed a nil Node. I can avoid the crash by adding an "if n == nil { return false }" to the test code, but what one supposed to do with a nil Node?

@go101

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@go101 go101 commented Nov 12, 2018

A nil node indicates the walking for children nodes is done. See the docs for details.

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@entrope entrope commented Nov 12, 2018

Well, I feel sheepish. Sorry for the noise, and thank you for the help.

@entrope entrope closed this Nov 12, 2018
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