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SubjectRe: [PATCH 1/3] arm64: perf: Mark expected switch fall-through
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.

If anything, it fixes:

d93512ef0f0e (" Makefile: Globally enable fall-through warning")

... given the commit message for that patch states:

Now that all the fall-through warnings have been addressed in the
kernel, enable the fall-through warning globally.

... and the existence of this patch implies otherwise.

IIUC that patch isn't even in mainline yet, but given this is simple I
imagine that Will and Catalin might be happy to pick this up for the
next rc.

Thanks,
Mark.

> ---
> arch/arm64/kernel/hw_breakpoint.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
> index dceb84520948..ea616adf1cf1 100644
> --- a/arch/arm64/kernel/hw_breakpoint.c
> +++ b/arch/arm64/kernel/hw_breakpoint.c
> @@ -535,14 +535,17 @@ int hw_breakpoint_arch_parse(struct perf_event *bp,
> case 0:
> /* Aligned */
> break;
> - case 1:
> - /* Allow single byte watchpoint. */
> - if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
> - break;
> case 2:
> /* Allow halfword watchpoints and breakpoints. */
> if (hw->ctrl.len == ARM_BREAKPOINT_LEN_2)
> break;
> + /* Fall through */
> + case 1:
> + case 3:
> + /* Allow single byte watchpoint. */
> + if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
> + break;
> + /* Fall through */
> default:
> return -EINVAL;
> }
> --
> 2.20.1
>

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