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Re: [Xen-devel] [RFC PATCH 0/4] Add missing default labels to switch statements

On 22/02/2019 11:21, Andrii Anisov wrote:
On 22.02.19 12:27, Andrew Cooper wrote:
On 22/02/2019 09:57, Oleksandr Andrushchenko wrote:
From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>

Hello, everybody!

We at EPAM Systems would like to present first series of patches targeting Xen
on ARM Functional Safety certification (ISO61508 based): implementation of
MISRA [1] C:2012 Rule 16.4 which requires that every switch statement has a
default label as a measure of defensive programming technique.

Hang on - what?

Can someone attempt to justify why actively breaking -Wswitch is going
to result in safer/better code?

I would express my vision of that MISRA rule requirement:
It requires handling (in any meaning) all possible incoming values explicitly.
Switching through enum still could be guarded by BUG/ASSERT_UNREACHABLE under default label. Though at runtime, not compilation time.

While review tend to be very thorough, it is sometimes hard to spot when we miss a case. This is where -Wswitch comes into place to spot missing how.

How the BUG/ASSERT_UNREACHABLE solution is going to help us here?


Julien Grall

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