Messages in this thread | | | Date | Wed, 9 May 2018 12:32:57 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH 4/9] arm: Split breakpoint validation into "check" and "commit" |
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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.
> 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?
Thanks, Mark.
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