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

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Message-ID: <20180607074628.kd3iyxevwj3ypzbr@intel.com>
Date:   Thu, 7 Jun 2018 15:46:29 +0800
From:   "Du, Changbin" <changbin.du@...el.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>, 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

Hi,
On Thu, Jun 07, 2018 at 09:47:18AM +0530, Viresh Kumar wrote:
> +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 ?
> 
I think if the destination is not a null terminated string (If I understand your
description below), memcpy can be used to get rid of such warning. The warning
makes sense in general as explained in mannual. Thanks!

> 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

-- 
Thanks,
Changbin Du