On 201116 1805, Andrey Konovalov wrote: > On Mon, Nov 16, 2020 at 9:35 AM Dmitry Vyukov <dvyu...@google.com> wrote: > > > > On Mon, Nov 16, 2020 at 3:39 AM Alexander Bulekov <alx...@bu.edu> wrote: > > > > > > Hello, > > > I'm trying to collect coverage over the syscalls issued by my process, > > > as well as the kthreads spawned as a result of these syscalls > > > (eg coverage over vhost ioctls and the worker kthread). Is there a way > > > to collect coverage with both KCOV_REMOTE_ENABLE(with common_handle) and > > > KCOV_ENABLE, simultaneously? > > > > > > Based on the code it seems that these two modes are mutually > > > exclusive within a single task, but I don't think this is mentioned in > > > the Documentation, so I want to make sure I'm not missing something. > > > > Hi Alex, > > > > Yes, it's probably not supported within a single task. The easiest way > > to verify is to try it ;) > > > > It is possible to collect both coverages, but you will need 2 threads > > (one just to set up remote KCOV). > > > > Unless I am missing any fundamental limitations, I would say it would > > be reasonable to support this within a single task as well. > > I think the reason we did that initially, is because we don't care > about normal coverage for USB emitting pseudo-syscalls. Filed a bug > for this: https://bugzilla.kernel.org/show_bug.cgi?id=210225
I'm interested in adding support for this. Looking through the code, I can think of ~two approaches: 1.) Allow the same kcov fd to be used to track coverage with both KCOV_REMOTE_ENABLE and KCOV_ENABLE. If we try to use the same coverage bitmap for both the remote and the local coverage, I think the local part would have to deal with the kcov_remote_lock. If the local part continues to write directly into the user-space coverage-area, as it does now, it seems it would require locking for each __sanitizer_cov call. Alternatively, the local and the remote parts could write into different coverage-bitmaps, but I'm not sure if there is a neat way to do this. 2.) Allow multiple kcov fds to be used by the same task. In the task, keep a linked-list of pointers to kcov objects (remote or local). For each __sanitizer_... call, walk the linked list and check if any of the kcov objects match the requirements (trace_cmp/trace_pc/remote). This would also have the side-effect of enabling simultaneous PC and CMP tracing. Of course, it seems that this would add some overhead (in the case of a single open fd, there would be extra pointer dereferences to get the area[], size, etc). Am I missing a better alternative? Thanks
