Hi -
> > Help me out here: by "kgdb extension" do you imagine "something new > > that an unprivileged user can use to debug his own process"? Or do > > you imagine a new userspace facility that single-steps the kernel? > > Is this a trick question? Single-stepping the kernel on the same system > [especially if it's an UP system] would certainly be a challenge ;-) > > What i mean is what i said: if you provide a new framework (especially > if it's user visible - which both kgdb and the gdb stub is) you should > either fully replace existing functionality or extend it. Overlapping it > in an incomplete way is not useful to anyone. But there is no "overlap" beyond the name. The functional scope of the two interfaces is totally non-overlapping, and are consistent with the current chasms between kernel- and user-side debugging. Sure, in the future, it may make sense to teach the kernel-side (kgdb serial console) interface to manipulate userspace. But that will require a gdb extension. And it would not satisfy an unprivileged user's need to debug pure userspace (in a better way than current ptrace can). This is why I keep asking for specificity as to this "new framework" you imagine. Just sharing definitions such as kgdb_arch/kgdb_io but otherwise completely disconnected (separate channels)? > Extending kgdb to allow the use of it as if we used gdb locally would > certainly be interesting - and then you could drop into the kernel > anytime as well. (Is this a restatement of the "trick question" idea?) > > > We dont want to separate facilities for the same conceptual thing: > > > examining application state (be that in user-space and > > > kernel-space). > > This seems like a shallow sort of consistency. kgdb was added after > > ptrace existed -- why not extend ptrace instead to target the kernel? > > After all, it's "examining application state". The answer is that it > > doesn't make a heck of a lot of sense. > > kgdb simply used gdb's preferred way of remote debugging. That's > certainly the ugliest bit of it btw - but it's an externality to kgdb. > Had it extended ptrace it wouldnt have gdb compatibility. So, because of a constraint for gdb compatibility, you built a separate interface for kgdb vs. ptrace. Fine. Do you accept that, even if a hypothetical single channel existed for which kernel- and user-space debugging could occur, current gdb is not compatible with this? So by your own reasoning, such a facility should not be mandated as a "necessary first step". > [...] perf replaces oprofile functionally. (I'm told that it's not a strict superset from a functional point of view, FWIW, something about a larger selection of low level hardware counters.) > If the in-kernel gdb stub replaced kgdb functionally you'd hear no > complaints from me. Let's leave it as an idea for the future. - FChE
