x/debug/cmd/viewcore: missing executable shows as panic

[rhysh]

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

$ go1.10 version
go version go1.10.4 darwin/amd64
$ (cd $(go list -f '{{.Dir}}' golang.org/x/debug/cmd/viewcore) && git rev-parse HEAD)
1ff449a1b670fb60da59e170803373318549b845

Does this issue reproduce with the latest release?

This is the latest revision of golang.org/x/debug/cmd/viewcore, golang/debug@1ff449a. It fails with go1.10.4 and also with go1.11.

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

I'm using a darwin/amd64 machine to load a linux/amd64 core dump.

$ go1.10 env
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/rhys/Library/Caches/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/rhys/go"
GORACE=""
GOROOT="/Users/rhys/go/version/go1.10"
GOTMPDIR=""
GOTOOLDIR="/Users/rhys/go/version/go1.10/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/49/zmds5zsn75z1283vtzxyfr5hj7yjq4/T/go-build447726636=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I ran viewcore with a core file. I did not specify an executable. The executable is not available on my machine at the path described in the core file.

What did you expect to see?

I expected an error message reminding me to specify the location of the executable with the --exe argument.

What did you see instead?

$ viewcore /path/to/core-file
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0xf0 pc=0x128f9a6]

goroutine 1 [running]:
debug/dwarf.(*Reader).Seek(0xc42190c000, 0xc400000000)
	/usr/local/go/src/debug/dwarf/entry.go:543 +0x76
debug/dwarf.(*Data).Reader(0x0, 0x0)
	/usr/local/go/src/debug/dwarf/entry.go:526 +0x5f
golang.org/x/debug/internal/gocore.(*Process).readDWARFTypes(0xc42190a000)
	/Users/rhys/go/src/golang.org/x/debug/internal/gocore/dwarf.go:22 +0x55
golang.org/x/debug/internal/gocore.Core(0xc420144000, 0x70, 0x0, 0x0)
	/Users/rhys/go/src/golang.org/x/debug/internal/gocore/process.go:141 +0xca
main.readCore(0x4, 0x4, 0x4, 0x3)
	/Users/rhys/go/src/golang.org/x/debug/cmd/viewcore/main.go:260 +0xd1
main.runRoot(0x169dde0, 0x16c1f38, 0x0, 0x0)
	/Users/rhys/go/src/golang.org/x/debug/cmd/viewcore/main.go:279 +0x47
golang.org/x/debug/cmd/viewcore/vendor/github.com/spf13/cobra.(*Command).execute(0x169dde0, 0xc42000c070, 0x0, 0x0, 0x169dde0, 0xc42000c070)
	/Users/rhys/go/src/golang.org/x/debug/cmd/viewcore/vendor/github.com/spf13/cobra/command.go:766 +0x2c1
golang.org/x/debug/cmd/viewcore/vendor/github.com/spf13/cobra.(*Command).ExecuteC(0x169dde0, 0xc420022580, 0x169e040, 0x169e2a0)
	/Users/rhys/go/src/golang.org/x/debug/cmd/viewcore/vendor/github.com/spf13/cobra/command.go:852 +0x30a
golang.org/x/debug/cmd/viewcore/vendor/github.com/spf13/cobra.(*Command).Execute(0x169dde0, 0x1447cf3, 0x1)
	/Users/rhys/go/src/golang.org/x/debug/cmd/viewcore/vendor/github.com/spf13/cobra/command.go:800 +0x2b
main.main()
	/Users/rhys/go/src/golang.org/x/debug/cmd/viewcore/main.go:238 +0xbf

CC @heschik

[randall77]

@hyangah

[gopherbot]

Change https://golang.org/cl/136516 mentions this issue: cmd/viewcore: don't panic because of missing executable