linux-kernel - Re: [PATCH RFC] video: fbdev: sis: condition with no effect

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.LNX.2.11.1502052134270.756@localhost>
Date:	Thu, 5 Feb 2015 23:37:23 +0000 (UTC)
From:	Scot Doyle <lkml14@...tdoyle.com>
To:	Tormod Volden <lists.tormod@...il.com>
cc:	Nicholas Mc Guire <hofrat@...dl.org>,
	Thomas Winischhofer <thomas@...ischhofer.net>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] video: fbdev: sis: condition with no effect

On Thu, 5 Feb 2015, Tormod Volden wrote:
> On Thu, Feb 5, 2015 at 9:45 PM, Scot Doyle wrote:
> > On Wed, 4 Feb 2015, Nicholas Mc Guire wrote:
> >> The if and the else branch code are identical - so the condition has no
> >> effect on the effective code - this patch removes the condition and the
> >> duplicated code.
> >>
> >> Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> >> ---
> >>
> >> This code has been in here since commit 544393fe584d ("sisfb update") so I guess it is
> >> safe to simply remove the duplicated code if nobody noticed for 10 years.
> >>
> >> Note that the code is not really CodingStyle compliant - the lines inserted were formatted
> >> to satisfy the coding style but I'm unsure if it is not better to leave it in the
> >> old format.
> >>
> >> Patch was only compile tested with x86_64_defconfig +
> >> CONFIG_FB_SIS=m, CONFIG_FB_SIS_300=y, CONFIG_FB_SIS_315=y
> >>
> >> Patch is against 3.19.0-rc7 (localversion-next is -next-20150204)
> >>
> >>  drivers/video/fbdev/sis/init301.c |    9 ++-------
> >>  1 file changed, 2 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/drivers/video/fbdev/sis/init301.c b/drivers/video/fbdev/sis/init301.c
> >> index 295e0de..9533a8ab 100644
> >> --- a/drivers/video/fbdev/sis/init301.c
> >> +++ b/drivers/video/fbdev/sis/init301.c
> >> @@ -7971,13 +7971,8 @@ SiS_SetCHTVReg(struct SiS_Private *SiS_Pr, unsigned short ModeNo, unsigned short
> >>           }
> >>        } else {                                               /* ---- PAL ---- */
> >>           /* We don't play around with FSCI in PAL mode */
> >> -         if(resindex == 0x04) {
> >> -            SiS_SetCH70xxANDOR(SiS_Pr,0x20,0x00,0xEF);       /* loop filter off */
> >> -            SiS_SetCH70xxANDOR(SiS_Pr,0x21,0x01,0xFE);       /* ACIV on */
> >> -         } else {
> >> -            SiS_SetCH70xxANDOR(SiS_Pr,0x20,0x00,0xEF);       /* loop filter off */
> >> -            SiS_SetCH70xxANDOR(SiS_Pr,0x21,0x01,0xFE);       /* ACIV on */
> >> -         }
> >> +       SiS_SetCH70xxANDOR(SiS_Pr, 0x20, 0x00, 0xEF); /* loop filter off */
> >> +       SiS_SetCH70xxANDOR(SiS_Pr, 0x21, 0x01, 0xFE); /* ACIV on */
> >>        }
> >>
> >>  #endif  /* 300 */
> >
> > The code covering the PAL case had this redundancy when it was introduced
> > in Linux 2.4.19.
> >
> > Lines 7934-7981 consider three variables: PAL, overscan, and resindex.
> > Given the "#ifdef 0" block, couldn't the current six sections collapse
> > into two? One for (!PAL && overscan && resindex==5) and another for the
> > rest?
> 
> Are we sure there isn't a typo in one of the duplicate clauses? Or
> wrong copy-pasting? Generally I am skeptical to "fixing" code without
> understanding what is behind or testing it, and just cosmetically
> brush over it. For now at least it is obvious that there is something
> wrong. In case (although an unlikely one) someone who understands the
> code and knows this chip comes along, he would quickly spot this.
> After your "fixups" this will be all forgotten. Additionally it adds
> to the impression that this code is being maintained, which is wrong.
> 
> I would understand an argument about annoying compiler warnings and
> the like, but in that case I would prefer to #if 0 it instead of
> "prettifying" it.
> 
> 0.02
> Tormod

Yes, I also wondered how this code came to be. The general intention of 
the code seems clear from the code comments and the diff between 2.4.18 
and 2.4.19. The redundancy pointed out in the patch existed in the !PAL 
case, and became obvious when copied and reduced to the PAL case.

Thanks for pointing out that it hasn't been maintained, I missed that.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/