Messages in this thread | | | Date | Tue, 15 May 2018 15:35:33 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 4/9] arm: Split breakpoint validation into "check" and "commit" |
| |
On Wed, May 09, 2018 at 12:32:57PM +0100, Mark Rutland wrote: > On Tue, May 08, 2018 at 12:13:23PM +0100, Mark Rutland wrote: > > Hi Frederick, > > > > On Sun, May 06, 2018 at 09:19:50PM +0200, Frederic Weisbecker wrote: > > > The breakpoint code mixes up attribute check and commit into a single > > > code entity. Therefore the validation may return an error due to > > > incorrect atributes while still leaving halfway modified architecture > > > breakpoint struct. > > > > > > Prepare fox fixing this misdesign and separate both logics. > > > > Could you elaborate on what the problem is? I would have expected that > > when arch_build_bp_info() returns an error code, we wouldn't > > subsequently use the arch_hw_breakpoint information. Where does that > > happen? > > From digging, I now see that this is a problem when > modify_user_hw_breakpoint() is called on an existing breakpoint. It > would be nice to mention that in the commit message.
Right, I'll improve the changelog.
> > > I also see that the check and commit hooks have to duplicate a > > reasonable amount of logic, e.g. the switch on bp->attr.type. Can we > > instead refactor the existing arch_build_bp_info() hooks to use a > > temporary arch_hw_breakpoint, and then struct assign it after all the > > error cases, > e.g. > > > > static int arch_build_bp_info(struct perf_event *bp) > > { > > struct arch_hw_breakpoint hbp; > > > > if (some_condition(bp)) > > hbp->field = 0xf00; > > > > switch (bp->attr.type) { > > case FOO: > > return -EINVAL; > > case BAR: > > hbp->other_field = 7; > > break; > > }; > > > > if (failure_case(foo)) > > return err; > > > > *counter_arch_bp(bp) = hbp; > > } > > > > ... or is that also problematic? > > IIUC, this *would* work, but it is a little opaque. > > Perhaps we could explicitly pass the temporary arch_hw_breakpoint in, > and have the core code struct-assign it after checking for errors?
Exactly, that looks like a good idea, I'm trying that.
Thanks.
| |