linux-kernel - Re: [PATCH v5 2/4] kernel hacking: new config NO_AUTO_INLINE to disable compiler auto-inline optimizations

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Date:   Thu, 7 Jun 2018 09:47:18 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     gregkh@...uxfoundation.org, alex.elder@...aro.org,
        Johan Hovold <johan@...nel.org>,
        kbuild test robot <lkp@...el.com>,
        linux-arch@...r.kernel.org, michal.lkml@...kovi.net,
        linux-kernel@...r.kernel.org, arnd@...db.de,
        yamada.masahiro@...ionext.com, lgirdwood@...il.com,
        broonie@...nel.org, rdunlap@...radead.org, x86@...nel.org,
        linux@...linux.org.uk, changbin.du@...el.com,
        linux-sparse@...r.kernel.org, mingo@...hat.com, kbuild-all@...org,
        akpm@...ux-foundation.org, changbin.du@...il.com,
        tglx@...utronix.de, linux-kbuild@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 2/4] kernel hacking: new config NO_AUTO_INLINE to
 disable compiler auto-inline optimizations

+Greg/Alex,

@Fegguang/build-bot: I do see mention of Greg and /me in your initial email's
body saying TO: Viresh, CC: Greg, but I don't see any of us getting cc'd in your
email. Bug ?

On 06-06-18, 14:26, Steven Rostedt wrote:
> On Wed, 6 Jun 2018 16:26:00 +0200
> Johan Hovold <johan@...nel.org> wrote:
> 
> > Looks like the greybus code above is working as intended by checking for
> > unterminated string after the strncpy, even if this does now triggers
> > the truncation warning.

So why exactly are we generating a warning here ? Is it because it is possible
that the first n bytes of src may not have the null terminating byte and the
dest may not be null terminated eventually ?

Maybe I should just use memcpy here then ?

But AFAIR, I used strncpy() specifically because it also sets all the remaining
bytes after the null terminating byte with the null terminating byte. And so it
is pretty easy for me to check if the final string is null terminated by
checking [max - 1] byte against '\0', which the code is doing right now.

I am not sure what would the best way to get around this incorrect-warning.

And I am wondering on why buildbot reported the warning only for two instances
in that file, while I have done the same thing at 4 places.

> Ah, yes I now see that. Thanks for pointing it out. But perhaps it
> should also add the "- 1" to the strncpy() so that gcc doesn't think
> it's a mistake.

The src string is passed on from a firmware entity and we need to make sure the
protocol (greybus) is implemented properly by the other end. For example, in the
current case if the firmware sends "HELLOWORLD", its an error as it should have
sent "HELLWORLD\0". But with what you are saying we will forcefully make dest as
"HELLWORLD\0", which wouldn't be the right thing to do as we will miss the bug
present in firmware.

-- 
viresh