Open mvdan opened 2 years ago
The docs do say:
The Skip method of *T can be used in a fuzz target if the input is invalid, but should not be considered a crash.
Still unclear to me if this means that the input can end up in the cached corpus inside the build cache or not - to my understanding, that would be the difference between go-fuzz's 0
and -1
.
cc @golang/fuzzing We should clarify this.
Currently T.Skip
does nothing specific to fuzzing; it's like returning early.
We should make sure that if T.Skip
is called, an input will not be considered "interesting" even if it provides new coverage. I think that would be equivalent to return -1
in go-fuzz.
So I guess go-fuzz's return 0
would be equivalent to just return
without t.Skip
? In that scenario I guess I'd mostly avoid t.Skip
in the context of fuzzing, just like I didn't need to use return -1
for go-fuzz. Some guidance on when or when not to use Skip would be certainly welcome.
Did you mean Go 1.19 here? Or is this Go 1.18?
1.19 most likely, though it would be nice to have for 1.18. There are already a lot of open release blockers to fix soon though.
CC @golang/fuzzing
What is the status of this issue? Thanks.
Change https://go.dev/cl/430676 mentions this issue: internal/fuzz: make T.Skip ignore inputs when fuzzing
The current "first class fuzzing" proposal design doc (https://go.googlesource.com/proposal/+/master/design/draft-fuzzing.md) only has one mention of "skip":
As I was porting one of my fuzz funcs from go-fuzz to first class fuzzing, I remembered that go-fuzz actually has two kinds of "skips":
So it seems like, with go-fuzz, you have three options: give priority (+1), must ignore (-1), or default behavior (0).
Personally, I only used +1 or 0 in my go-fuzz funcs; I never had any input that must never be added to the corpus. I've adapted those returns for the new fuzzer so that the
return 1
is now a regular return ending the function, andreturn 0
is now at.Skip
to signal an uninteresting input. Here's an example: https://github.com/mvdan/sh/commit/e186e04cbf119ac6e51d2010cb37674374557046I'd love it if the meaning of
t.Skip
in the context of fuzz funcs was better documented. Perhaps my understanding of what it does is incorrect, or perhaps it doesn't correspond toreturn 0
in go-fuzz.Another question is whether we want an equivalent to go-fuzz's
return -1
. I personally didn't have a need for it, but others might be using it and not know how to transition those to the new fuzzer.cc @katiehockman