Messages in this thread |  | | Subject | Re: [PATCH 1/3] arm64: perf: Mark expected switch fall-through | From | Robin Murphy <> | Date | Fri, 26 Jul 2019 13:38:24 +0100 |
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On 26/07/2019 13:27, Will Deacon wrote: > On Fri, Jul 26, 2019 at 01:13:54PM +0100, Mark Rutland wrote: >> On Fri, Jul 26, 2019 at 01:10:57PM +0100, Mark Rutland wrote: >>> On Fri, Jul 26, 2019 at 01:27:16PM +0200, Anders Roxell wrote: >>>> When fall-through warnings was enabled by default, commit d93512ef0f0e >>>> ("Makefile: Globally enable fall-through warning"), the following >>>> warnings was starting to show up: >>>> >>>> ../arch/arm64/kernel/hw_breakpoint.c: In function ‘hw_breakpoint_arch_parse’: >>>> ../arch/arm64/kernel/hw_breakpoint.c:540:7: warning: this statement may fall >>>> through [-Wimplicit-fallthrough=] >>>> if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1) >>>> ^ >>>> ../arch/arm64/kernel/hw_breakpoint.c:542:3: note: here >>>> case 2: >>>> ^~~~ >>>> ../arch/arm64/kernel/hw_breakpoint.c:544:7: warning: this statement may fall >>>> through [-Wimplicit-fallthrough=] >>>> if (hw->ctrl.len == ARM_BREAKPOINT_LEN_2) >>>> ^ >>>> ../arch/arm64/kernel/hw_breakpoint.c:546:3: note: here >>>> default: >>>> ^~~~~~~ >>>> >>>> Rework so that the compiler doesn't warn about fall-through. Rework so >>>> the code looks like the arm code. Since the comment in the function >>>> indicates taht this is supposed to behave the same way as arm32 because >>> >>> Typo: s/taht/that/ >>> >>>> it handles 32-bit tasks also. >>>> >>>> Cc: stable@vger.kernel.org # v3.16+ >>>> Fixes: 6ee33c2712fc ("ARM: hw_breakpoint: correct and simplify alignment fixup code") >>>> Signed-off-by: Anders Roxell <anders.roxell@linaro.org> >>> >>> The patch itself looks fine, but I don't think this needs a CC to >>> stable, nor does it require that fixes tag, as there's no functional >>> problem. >> >> Hmm... I now see I spoke too soon, and this is making the 1-byte >> breakpoint work at a 3-byte offset. > > I still don't think it's quite right though, since it forbids a 2-byte > watchpoint on a byte-aligned address.
Plus, AFAICS, a 1-byte watchpoint on a 2-byte-aligned address.
Not that I know anything about this code, but it does start to look like it might want rewriting without the offending switch statement anyway. At a glance, it looks like the intended semantic might boil down to:
if (hw->ctrl.len > offset) return -EINVAL;
Robin.
> I think the arm64 code matches what we had on 32-bit prior to > d968d2b801d8 ("ARM: 7497/1: hw_breakpoint: allow single-byte watchpoints > on all addresses"), so we should have one patch bringing us up to speed > with that change, and then another annotating the fallthroughs. > > Will > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >
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