Brainstorming new kernel interfaces for rr

Chris Jones jones.chris.g at
Thu Feb 27 12:32:34 PST 2014

I created to better
track this list.


On Tue, Feb 25, 2014 at 9:29 PM, Chris Jones <jones.chris.g at>wrote:

> I don't want to distract anyone from 1.0, but we've run into enough
> tracing shortcomings that I think we can start putting together a "kernel
> wishlist".  This stuff can take awhile to trickle out to where rr users
> will be able to take advantage, so it makes sense to front load.  Here's my
> strawman list
>  - in-kernel buffering of syscall outparam data.  Syscallbuf+vsyscall
> hooking works OK in practice, but the kernel can do so much better, so much
> more easily.  Essentially it "just" has to record copy_to_user() within
> syscall handlers, plus a bit of metadata.  Perhaps could be exposed through
> perf_event.
>  - trapping on CPUID, like the RDTSC traps.  Modern Intel chips can do
> this.
>  - expose Branch Trace Store data, probably through perf_event.  There was
> a previous attempt to do this, but I think it fizzled out.
>  - implement a way for ptrace tracers to efficiently wait on a tracee's
> private futex
>  - we hit a pwrite64/pread64 bug that we shouldn't let slip through the
> cracks
> Anything else to add?
> Cheers,
> Chris
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