linux-kernel - Re: [PATCH v2 1/3] staging/fbtft: Remove all strcpy() uses

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Date:   Sun, 25 Jul 2021 21:51:18 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Len Baker <len.baker@....com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Phil Reid <preid@...ctromag.com.au>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "open list:FRAMEBUFFER LAYER" <linux-fbdev@...r.kernel.org>,
        linux-staging@...ts.linux.dev,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] staging/fbtft: Remove all strcpy() uses

On Sun, Jul 25, 2021 at 4:59 PM Len Baker <len.baker@....com> wrote:
> On Sat, Jul 24, 2021 at 11:21:04PM +0300, Andy Shevchenko wrote:
> > On Sat, Jul 24, 2021 at 7:05 PM Len Baker <len.baker@....com> wrote:

...

> > > -       char msg[128];
> >
> > 128 / 4 = 32. So, this buffer is enough to debug print only up to 32
> > bytes. Hence %*ph replacement won't cut output earlier than requested.
>
> I'm sorry, but I don't understand what you are trying to explain. Moreover,
> with the "0x%02X " in the sprintf followed by the strcat, the msg buffer can
> print 128/5 values (25 hex values).
>
> The %*ph replacement can print up to 64 bytes, so I don't see any problem
> here.

Right. That's what I am trying to say and the hint here is to combine
this part into a phrase in the commit message in the next version of
the patch.

...

> > > +                       for (j = i + 1; par->init_sequence[j] >= 0; j++);
> >
> > Why is i + 1 initial for the j? You may rather access the 'i + 1 +
> > j'th element in the array...
> >
> > ...
> >
> > > +                                     par->init_sequence[i], j - i - 1,
> >
> > ...and get rid of the ' - i -1' part here.
>
> Yes, it was the first idea but I prefer this method since we save aritmethic
> operations. In other words, if I use what you suggest, the index for
> par->init_sequence is calculated as a "sum" every iteration. But if the
> performance is not an issue and you believe that the above is more clear, I
> have no problem. What do you prefer?

I prefer my variant and I believe the compilers nowadays are clever
enough to understand this. Have you tried to compile and compare the
real assembly?

-- 
With Best Regards,
Andy Shevchenko