Re: [Nouveau] [PATCH 000/141] Fix fall-through warnings for Clang
On Sun, 2020-11-22 at 10:25 -0800, Joe Perches wrote: > On Sun, 2020-11-22 at 10:21 -0800, James Bottomley wrote: > > Please tell me our reward for all this effort isn't a single > > missing error print. > > There were quite literally dozens of logical defects found > by the fallthrough additions. Very few were logging only. So can you give us the best examples (or indeed all of them if someone is keeping score)? hopefully this isn't a US election situation ... James ___ Nouveau mailing list Nouveau@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/nouveau
Re: [Nouveau] [PATCH 000/141] Fix fall-through warnings for Clang
On Sun, 2020-11-22 at 11:22 -0800, Joe Perches wrote: > On Sun, 2020-11-22 at 11:12 -0800, James Bottomley wrote: > > On Sun, 2020-11-22 at 10:25 -0800, Joe Perches wrote: > > > On Sun, 2020-11-22 at 10:21 -0800, James Bottomley wrote: > > > > Please tell me our reward for all this effort isn't a single > > > > missing error print. > > > > > > There were quite literally dozens of logical defects found > > > by the fallthrough additions. Very few were logging only. > > > > So can you give us the best examples (or indeed all of them if > > someone is keeping score)? hopefully this isn't a US election > > situation ... > > Gustavo? Are you running for congress now? > > https://lwn.net/Articles/794944/ That's 21 reported fixes of which about 50% seem to produce no change in code behaviour at all, a quarter seem to have no user visible effect with the remaining quarter producing unexpected errors on obscure configuration parameters, which is why no-one really noticed them before. James ___ Nouveau mailing list Nouveau@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/nouveau
Re: [Nouveau] [PATCH 000/141] Fix fall-through warnings for Clang
On Sun, 2020-11-22 at 11:12 -0800, James Bottomley wrote: > On Sun, 2020-11-22 at 10:25 -0800, Joe Perches wrote: > > On Sun, 2020-11-22 at 10:21 -0800, James Bottomley wrote: > > > Please tell me our reward for all this effort isn't a single > > > missing error print. > > > > There were quite literally dozens of logical defects found > > by the fallthrough additions. Very few were logging only. > > So can you give us the best examples (or indeed all of them if someone > is keeping score)? hopefully this isn't a US election situation ... Gustavo? Are you running for congress now? https://lwn.net/Articles/794944/ ___ Nouveau mailing list Nouveau@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/nouveau
Re: [Nouveau] [PATCH 000/141] Fix fall-through warnings for Clang
On Sun, Nov 22, 2020 at 7:22 PM James Bottomley wrote: > > Well, it's a problem in an error leg, sure, but it's not a really > compelling reason for a 141 patch series, is it? All that fixing this > error will do is get the driver to print "oh dear there's a problem" > under four more conditions than it previously did. > > We've been at this for three years now with nearly a thousand patches, > firstly marking all the fall throughs with /* fall through */ and later > changing it to fallthrough. At some point we do have to ask if the > effort is commensurate with the protection afforded. Please tell me > our reward for all this effort isn't a single missing error print. It isn't that much effort, isn't it? Plus we need to take into account the future mistakes that it might prevent, too. So even if there were zero problems found so far, it is still a positive change. I would agree if these changes were high risk, though; but they are almost trivial. Cheers, Miguel ___ Nouveau mailing list Nouveau@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/nouveau
Re: [Nouveau] [PATCH 000/141] Fix fall-through warnings for Clang
On Sun, 2020-11-22 at 10:21 -0800, James Bottomley wrote: > Please tell me > our reward for all this effort isn't a single missing error print. There were quite literally dozens of logical defects found by the fallthrough additions. Very few were logging only. ___ Nouveau mailing list Nouveau@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/nouveau
Re: [Nouveau] [PATCH 000/141] Fix fall-through warnings for Clang
On Sun, 2020-11-22 at 08:17 -0800, Kees Cook wrote: > On Fri, Nov 20, 2020 at 11:51:42AM -0800, Jakub Kicinski wrote: > > On Fri, 20 Nov 2020 11:30:40 -0800 Kees Cook wrote: > > > On Fri, Nov 20, 2020 at 10:53:44AM -0800, Jakub Kicinski wrote: > > > > On Fri, 20 Nov 2020 12:21:39 -0600 Gustavo A. R. Silva wrote: > > > > > This series aims to fix almost all remaining fall-through > > > > > warnings in order to enable -Wimplicit-fallthrough for Clang. > > > > > > > > > > In preparation to enable -Wimplicit-fallthrough for Clang, > > > > > explicitly add multiple break/goto/return/fallthrough > > > > > statements instead of just letting the code fall through to > > > > > the next case. > > > > > > > > > > Notice that in order to enable -Wimplicit-fallthrough for > > > > > Clang, this change[1] is meant to be reverted at some point. > > > > > So, this patch helps to move in that direction. > > > > > > > > > > Something important to mention is that there is currently a > > > > > discrepancy between GCC and Clang when dealing with switch > > > > > fall-through to empty case statements or to cases that only > > > > > contain a break/continue/return statement[2][3][4]. > > > > > > > > Are we sure we want to make this change? Was it discussed > > > > before? > > > > > > > > Are there any bugs Clangs puritanical definition of fallthrough > > > > helped find? > > > > > > > > IMVHO compiler warnings are supposed to warn about issues that > > > > could be bugs. Falling through to default: break; can hardly be > > > > a bug?! > > > > > > It's certainly a place where the intent is not always clear. I > > > think this makes all the cases unambiguous, and doesn't impact > > > the machine code, since the compiler will happily optimize away > > > any behavioral redundancy. > > > > If none of the 140 patches here fix a real bug, and there is no > > change to machine code then it sounds to me like a W=2 kind of a > > warning. > > FWIW, this series has found at least one bug so far: > https://lore.kernel.org/lkml/CAFCwf11izHF=g1mGry1fE5kvFFFrxzhPSM6qKAO8gxSp=kr...@mail.gmail.com/ Well, it's a problem in an error leg, sure, but it's not a really compelling reason for a 141 patch series, is it? All that fixing this error will do is get the driver to print "oh dear there's a problem" under four more conditions than it previously did. We've been at this for three years now with nearly a thousand patches, firstly marking all the fall throughs with /* fall through */ and later changing it to fallthrough. At some point we do have to ask if the effort is commensurate with the protection afforded. Please tell me our reward for all this effort isn't a single missing error print. James ___ Nouveau mailing list Nouveau@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/nouveau
Re: [Nouveau] [PATCH 000/141] Fix fall-through warnings for Clang
On Fri, Nov 20, 2020 at 11:51:42AM -0800, Jakub Kicinski wrote: > On Fri, 20 Nov 2020 11:30:40 -0800 Kees Cook wrote: > > On Fri, Nov 20, 2020 at 10:53:44AM -0800, Jakub Kicinski wrote: > > > On Fri, 20 Nov 2020 12:21:39 -0600 Gustavo A. R. Silva wrote: > > > > This series aims to fix almost all remaining fall-through warnings in > > > > order to enable -Wimplicit-fallthrough for Clang. > > > > > > > > In preparation to enable -Wimplicit-fallthrough for Clang, explicitly > > > > add multiple break/goto/return/fallthrough statements instead of just > > > > letting the code fall through to the next case. > > > > > > > > Notice that in order to enable -Wimplicit-fallthrough for Clang, this > > > > change[1] is meant to be reverted at some point. So, this patch helps > > > > to move in that direction. > > > > > > > > Something important to mention is that there is currently a discrepancy > > > > between GCC and Clang when dealing with switch fall-through to empty > > > > case > > > > statements or to cases that only contain a break/continue/return > > > > statement[2][3][4]. > > > > > > Are we sure we want to make this change? Was it discussed before? > > > > > > Are there any bugs Clangs puritanical definition of fallthrough helped > > > find? > > > > > > IMVHO compiler warnings are supposed to warn about issues that could > > > be bugs. Falling through to default: break; can hardly be a bug?! > > > > It's certainly a place where the intent is not always clear. I think > > this makes all the cases unambiguous, and doesn't impact the machine > > code, since the compiler will happily optimize away any behavioral > > redundancy. > > If none of the 140 patches here fix a real bug, and there is no change > to machine code then it sounds to me like a W=2 kind of a warning. FWIW, this series has found at least one bug so far: https://lore.kernel.org/lkml/CAFCwf11izHF=g1mGry1fE5kvFFFrxzhPSM6qKAO8gxSp=kr...@mail.gmail.com/ -- Kees Cook ___ Nouveau mailing list Nouveau@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/nouveau
