coverage bug when using goto labelled statement

[jscrockett01]

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Coverage instrumentation is incorrect for labelled statements that are the target of a goto. This bug has been fixed in go's cmd/cover here:

https://github.com/golang/go/issues/16624

https://go-review.googlesource.com/#/c/30977/

[dvyukov]

Is it actually an issue for go-fuzz? "not reporting 100% coverage" should not affect go-fuzz.

[jscrockett01]

It's only an issue in the sense that basic blocks around labeled statements are not all enumerated, so transitions between these states are missed when looking for additional coverage by fuzz inputs. It doesn't prevent the fuzzer from operating; it just doesn't have awareness of those states.

On Wed, Feb 22, 2017 at 1:37 AM Dmitry Vyukov [email protected] wrote:

Is it actually an issue for go-fuzz? "not reporting 100% coverage" should not affect go-fuzz.

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[josharian]

I believe the best fix here is to rewrite our coverage instruction to use cmd/internal/edit, at which point we can benefit from improvements made to cmd/cover. Related: https://github.com/golang/go/issues/29824. Ultimately it would be nice to merge the two of them, but using the same basic mechanism is a good start towards that goal.

Unfortunately, switching to cmd/internal/edit is not as simple as it sounds. I tried to do it as part of the switch to go/packages and eventually gave up. It is possible...just complicated.