cmd/link: segfault given a text section named after a type

[pwaller]

Go1.8-rc1

Go env output

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/pwaller/.local"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build905941285=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

The following code crashes the linker. Granted, it is incorrect, but I encountered this by accident in a medium sized code base and it was difficult to figure out what was going wrong.

The linker crashes given this main.go and main.s.

main.go

package main

type FooType struct{}

type T1 struct{}

func (t1 *T1) MakeFoo() *FooType { return nil }

func main() {
	var t1 *T1
	_ = t1.MakeFoo
}

main.s

TEXT ·FooType(SB),0,$0

Output

# github.com/pwaller/crash/go-1.8rc1-linker
go.info.*github.com/pwaller/crash/go-1.8rc1-linker/pkg.FooType: unreachable sym in relocation: go.info.github.com/pwaller/crash/go-1.8rc1-linker/pkg.FooType
go.info.*github.com/pwaller/crash/go-1.8rc1-linker/pkg.FooType: missing DWARF section for relocation target go.info.github.com/pwaller/crash/go-1.8rc1-linker/pkg.FooType
go.info.github.com/pwaller/crash/go-1.8rc1-linker/pkg.FooType: unreachable symbol in symaddr
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x52941e]

goroutine 1 [running]:
cmd/link/internal/ld.relocsym(0xc4204ee000, 0xc42050ce80)
	/usr/local/go/src/cmd/link/internal/ld/data.go:589 +0x26ae
cmd/link/internal/ld.(*Link).reloc(0xc4204ee000)
	/usr/local/go/src/cmd/link/internal/ld/data.go:739 +0x128
cmd/link/internal/ld.Main()
	/usr/local/go/src/cmd/link/internal/ld/main.go:207 +0x949
main.main()
	/usr/local/go/src/cmd/link/main.go:58 +0xdb

[bradfitz]

Is this a regression from Go 1.7?

[pwaller]

It appears so, I just tested with go 1.7 and this did not crash. It did not give any warning either.

[bradfitz]

@ianlancetaylor, thoughts?

[ianlancetaylor]

It's unfortunate that the linker crashes, but I don't see any way to turn this code into a correct program. I think that we should fix the linker to report an error message and not crash, but we can do that for 1.9.

[jessfraz]

this doesnt crash the linker anymore on tip

[ianlancetaylor]

@jessfraz Thanks, closing.