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SubjectRe: [PATCH] USB: serial: io_edgeport: mark expected switch fall-throughs

Quoting Bjørn Mork <bjorn@mork.no>:

> "Gustavo A. R. Silva" <garsilva@embeddedor.com> writes:
>
>> In preparation to enabling -Wimplicit-fallthrough, mark switch cases
>> where we are expecting to fall through.
>>
>> Notice that in this particular case I replaced "...drop on through"
>> comments with a proper "fall through" comment on its own line, which
>> is what GCC is expecting to find.
>
> Sounds to me like GCC is the wrong tool for this. But I would of course
> not mind if it was *just* the text. However, as your patch cleary
> shows, the simplified logic leads to real problems:
>
>> @@ -1819,8 +1819,8 @@ static void process_rcvd_data(struct
>> edgeport_serial *edge_serial,
>> edge_serial->rxState = EXPECT_DATA;
>> break;
>> }
>> - /* Else, drop through */
>> }
>> + /* fall through */
>> case EXPECT_DATA: /* Expect data */
>> if (bufferLength < edge_serial->rxBytesRemaining) {
>> rxLen = bufferLength;
>
>
> The original comment clearly marked a *conditional* fall through at the
> correct place. Your patch makes it appear as if there is an
> unconditional fall through here. There is not. The fallthrough only
> applies to one of a number of nested if blocks. There are no less than
> 3 break statements in the same case block.
>

I see.
You are right.

> Not a big deal maybe, just as the lack of any "fall through" comment
> isn't a big deal in the first place. But this change is clearly making
> this code harder to read, and the change is therefore harmful IMHO.
>
> If you can't make -Wimplicit-fallthrough work without removing such
> precise fallthrough markings, then my proposal is to drop it and use
> some other tool.
>

I will talk with the hardening guys to see what we can do about this.

I appreciate for your comments.
Thanks
--
Gustavo A. R. Silva




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