nil pointer dereference when using -deps

[kortschak]

A nil pointer dereference occurs when gocov is run with the -deps option. Below shows the output from:

gocov test -deps > /dev/null

in code.google.com/p/biogo.step, but similar output occurs in any package I try.

Using -exclude='math/rand' prevents this panic which is due to calling (*Statement).At() on a nil receiver. gocov test math/rand gives essentially the same failure as expected.

This is presumably because math/rand depends on sync/atomic which is excluded from testing by gocov.

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x18 pc=0x5a30b3]

goroutine 1 [running]:
sync/atomic.AddUint64(0x18, 0x1, 0x0, 0x0, 0x572b8d, ...)
/tmp/gocov810177481/src/pkg/sync/atomic/asm_amd64.s:58 +0xd
github.com/axw/gocov.(_Statement).At(0x0, 0xf84019b960)
/tmp/gocov810177481/src/pkg/github.com/axw/gocov/gocov.go:329 +0x33
math/rand.(_rngSource).Seed(0xf840154000, 0x1, 0xf8400f90a8, 0x4)
/tmp/gocov810177481/src/pkg/math/rand/rng.go:237 +0x28
math/rand.NewSource(0x1, 0x160e00001601, 0xf84021d720, 0x70e78c)
/tmp/gocov810177481/src/pkg/math/rand/rand.go:105 +0x68
math/rand.init()
/tmp/gocov810177481/src/pkg/math/rand/zipf.go:-390 +0x1f61
code.google.com/p/biogo%2estep.init()
/tmp/gocov810177481/src/pkg/code.google.com/p/biogo.step/step.go:14 +0x5b
main.init()
code.google.com/p/biogo.step/_test/_testmain.go:18 +0x3b

[axw]

Sounds like this bug I filed against gc a while ago: http://code.google.com/p/go/issues/detail?id=3824
I don't think the fix went into 1.0.3, so you'll probably have to go to tip or wait on 1.1.

[kortschak]

The code Rémy posted on that bug works fine in the playground and the commit marked as fixing the issue went in on Jul30, but go1.0.3 was tagged Sep24, so I don't think they are the same bug. It's not a big issue though.

I'll try repeating it with tip... OK, that works without error.

[axw]

I think 1.0.3 was branched off an earlier revision, and fixed selectively back ported. I may be wrong though - and yeah I guess it doesn't really matter if it works now.

Thanks for verifying.