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| From | Arnd Bergmann <arnd@arndb.de> |
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH v2] staging/comedi/dt282x: avoid integer overflow warning |
| Date | Thu, 17 Mar 2016 17:10:02 +0100 |
| Message-ID | <rdIEO-1aN-27@gated-at.bofh.it> (permalink) |
| References | <rdqHT-5Ja-11@gated-at.bofh.it> <rdIlr-MU-3@gated-at.bofh.it> |
| X-Original-To | Hartley Sweeten <HartleyS@visionengravers.com> |
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| Sender | robomod@news.nic.it |
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| Approved | robomod@news.nic.it |
| Lines | 51 |
| Organization | linux.* mail to news gateway |
| X-Original-Cc | Ian Abbott <abbotti@mev.co.uk>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, "devel@driverdev.osuosl.org" <devel@driverdev.osuosl.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org> |
| X-Original-Date | Thu, 17 Mar 2016 17:08:34 +0100 |
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| X-Original-Sender | linux-kernel-owner@vger.kernel.org |
| Xref | csiph.com linux.kernel:1359985 |
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On Thursday 17 March 2016 15:47:57 Hartley Sweeten wrote: > On Wednesday, March 16, 2016 1:51 PM, Arnd Bergmann wrote: > > Is this a gcc-6 specific issue? Seems line this warning should be showing > up in a lot of drivers. Yes, I did not see this before moving to gcc-6.0, but this is the only driver I've encountered the warning for, in around 7000 randconfig builds. > > The warning makes sense, though the code is correct as far as I > > can tell. > > > > This disambiguates the operation by making the constant expressions > > we pass here explicitly 'unsigned', which helps to avoid the warning. > > > > As pointed out by Hartley Sweeten, scripts/checkpatch.pl notices that > > the shifts here are rather unreadable, though the suggested BIT() > > macro wouldn't work either. I'm changing it to a hexadecimal notation, > > which hopefully improves readability. I'm leaving the DT2821_CHANCSR_PRESLA > > alone because it seems wrong. > > BIT() should work for the ones pointed out by checpatch.pl. > > I would argue that the hexadecimal notation is still rather unreadable. > These ones make my head hurt... > > -#define DT2821_ADCSR_GS(x) (((x) & 0x3) << 4) > +#define DT2821_ADCSR_GS(x) (0x0030u & ((x) << 4)) > > -#define DT2821_DACSR_YSEL(x) ((x) << 9) > +#define DT2821_DACSR_YSEL(x) (0x7e00u & (x) << 9) > > -#define DT2821_SUPCSR_DS_PIO (0 << 10) > -#define DT2821_SUPCSR_DS_AD_CLK (1 << 10) > -#define DT2821_SUPCSR_DS_DA_CLK (2 << 10) > -#define DT2821_SUPCSR_DS_AD_TRIG (3 << 10) > +#define DT2821_SUPCSR_DS_PIO (0x0c00u & (0u << 10)) > +#define DT2821_SUPCSR_DS_AD_CLK (0x0c00u & (1u << 10)) > +#define DT2821_SUPCSR_DS_DA_CLK (0x0c00u & (2u << 10)) > +#define DT2821_SUPCSR_DS_AD_TRIG (0x0c00u & (3u << 10)) Feel free to come up with a different patch. I've put the patch on my 'submitted' stack for now and will get back to it after 4.7-rc1 if the warning remains. > Also, most of the comedi drivers use the BIT() macro. Are you planning on > changing all of them to use hexadecimal notation? No. Arnd
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[PATCH v2] staging/comedi/dt282x: avoid integer overflow warning Arnd Bergmann <arnd@arndb.de> - 2016-03-16 22:00 +0100
Re: [PATCH v2] staging/comedi/dt282x: avoid integer overflow warning Ian Abbott <abbotti@mev.co.uk> - 2016-03-17 11:30 +0100
RE: [PATCH v2] staging/comedi/dt282x: avoid integer overflow warning Hartley Sweeten <HartleyS@visionengravers.com> - 2016-03-17 16:50 +0100
Re: [PATCH v2] staging/comedi/dt282x: avoid integer overflow warning Arnd Bergmann <arnd@arndb.de> - 2016-03-17 17:10 +0100
RE: [PATCH v2] staging/comedi/dt282x: avoid integer overflow warning Hartley Sweeten <HartleyS@visionengravers.com> - 2016-03-17 18:00 +0100
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