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how to identify kernel build in grub menu
by Sumit Kumar April 29, 2018

April 29, 2018

Hi, I built a kernel for the first time following this guide : https://kernelnewbies.org/OutreachyfirstpatchSetup I rebooted my ubuntu machine and went to the grub menu and then chose advanced option menu. I could see 5-6 different choices listed as Ubuntu with different versions: 1. Are they all referring to some kernel build ? 2. If so, how do I identify my build from the rest of the builds ? Is there a way to name my build so that I can easily identify it ? My grub options looked like these : 1. https://www.google.co.in/search?q=ubuntu+grub+advanced+options&source=lnms&…: 2. https://www.google.co.in/search?q=ubuntu+grub+advanced+options&source=lnms&…: -- Thanks and Regards, Sumit

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Re: [PATCH] sched/fair: Change sched_feat(x) in !CONFIG_SCHED_DEBUG case
by Lukas Bulwahn April 23, 2018

April 23, 2018

On Fri, 20 Apr 2018, Peter Zijlstra wrote: > On Fri, Apr 20, 2018 at 06:29:07PM +0200, Philipp Klocke wrote: > > The gain is stopping a warning that clutters the output log of clang. > > Well, you should not be using clang anyway. It is known to miscompile > the kernel. > There are some advantages of having a second compiler that can compile the kernel (https://lwn.net/Articles/734071/) Some people in the kernel community and LLVM community are trying to get that to work. We also want a zero-warning policy for clang, similar to gcc. Hence, this motivates to have a look at those few clang warnings and come up with patches for them. This does not imply to make changes at any cost, and we need to determine a proper patch to either change the source code, disable the warning in the build script or annotate the file with some clang-specific pragmas. To us, a minor change in the source sounded most reasonable after looking at all three possible patches. Philipp might need another iteration, but it generally looks sound to me if we get the details flattened out. Lukas

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unable to build kernel
by Sumit Kumar April 22, 2018

April 22, 2018

Hi, I am unable to build kernel. Can anyone please help ? I am following steps from here: https://kernelnewbies.org/OutreachyfirstpatchSetup sumitsum@sumit-personal:~/Documents/linux_kernel/git/kernels/staging$ make -j3 YACC scripts/kconfig/zconf.tab.c /bin/sh: 1: bison: not found scripts/Makefile.lib:210: recipe for target 'scripts/kconfig/zconf.tab.c' failed make[2]: *** [scripts/kconfig/zconf.tab.c] Error 127 make[2]: *** Waiting for unfinished jobs.... LEX scripts/kconfig/zconf.lex.c /bin/sh: 1: flex: not found scripts/Makefile.lib:195: recipe for target 'scripts/kconfig/zconf.lex.c' failed make[2]: *** [scripts/kconfig/zconf.lex.c] Error 127 Makefile:525: recipe for target 'syncconfig' failed make[1]: *** [syncconfig] Error 2 make: *** No rule to make target 'include/config/auto.conf', needed by 'include/config/kernel.release'. Stop. make: *** Waiting for unfinished jobs.... -- Thanks and Regards, Sumit

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when to use make olddefconfig
by Sumit Kumar April 22, 2018

April 22, 2018

Hi, I was going through this link : https://kernelnewbies.org/OutreachyfirstpatchSetup , and came across the make olddefconfig cmd. The explanation on the web page is very confusing. Can anyone please explain in simpler way when "make olddefconfig" cmd is intended to be used ? The webpage says this : If you need to make any changes to your configuration, run this command to silently update any new configuration values to their default. -- Thanks and Regards, Sumit

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Re: make olddefconfig cmd failing
by Alex Arvelaez April 22, 2018

April 22, 2018

On Apr 21, 2018 7:11 AM, Sumit Kumar <sumit686215(a)gmail.com> wrote: > > Hi, > > I was following instructions given on this web page: https://kernelnewbies.org/OutreachyfirstpatchSetup > > I get errors when I execute make olddefconfig cmd: > > sumitsum@sumit-personal:~/Documents/linux_kernel/git/kernels/staging$ make olddefconfig > HOSTCC scripts/basic/fixdep > HOSTCC scripts/kconfig/conf.o > YACC scripts/kconfig/zconf.tab.c > /bin/sh: 1: bison: not found You need to install bison. Make sure to install all other build dependencies as well (there's a list in the kernel docs). > scripts/Makefile.lib:210: recipe for target 'scripts/kconfig/zconf.tab.c' failed > make[1]: *** [scripts/kconfig/zconf.tab.c] Error 127 > Makefile:525: recipe for target 'olddefconfig' failed > make: *** [olddefconfig] Error 2 Regards, Alex

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How can I disable compile optimization in kernel for friendly debugging, Thanks
by sizel April 21, 2018

April 21, 2018

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make olddefconfig cmd failing
by Sumit Kumar April 21, 2018

April 21, 2018

Hi, I was following instructions given on this web page: https://kernelnewbies.org/OutreachyfirstpatchSetup I get errors when I execute make olddefconfig cmd: sumitsum@sumit-personal:~/Documents/linux_kernel/git/kernels/staging$ make olddefconfig HOSTCC scripts/basic/fixdep HOSTCC scripts/kconfig/conf.o YACC scripts/kconfig/zconf.tab.c /bin/sh: 1: bison: not found scripts/Makefile.lib:210: recipe for target 'scripts/kconfig/zconf.tab.c' failed make[1]: *** [scripts/kconfig/zconf.tab.c] Error 127 Makefile:525: recipe for target 'olddefconfig' failed make: *** [olddefconfig] Error 2 -- Thanks and Regards, Sumit

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Re: [PATCH] sched/fair: Change sched_feat(x) in !CONFIG_SCHED_DEBUG case
by Philipp Klocke April 20, 2018

April 20, 2018

On 20.04.2018 09:57, Peter Zijlstra wrote: > On Mon, Apr 16, 2018 at 10:54:26AM +0200, Philipp Klocke wrote: > >> This patch is motivated by the clang warning Wconstant-logical-operand, >> issued when logically comparing a variable to a constant integer that is >> neither 1 nor 0. It happens for sched_feat(x) when sysctl_sched_features >> is constant, i.e., CONFIG_SCHED_DEBUG is not set. >> >> kernel/sched/fair.c:3927:14: warning: use of logical '&&' with constant operand [-Wconstant-logical-operand] >> if (initial && sched_feat(START_DEBIT)) >> ^ ~~~~~~~~~~~~~~~~~~~~~~~ >> kernel/sched/fair.c:3927:14: note: use '&' for a bitwise operation >> if (initial && sched_feat(START_DEBIT)) >> ^~ >> & >> kernel/sched/fair.c:3927:14: note: remove constant to silence this warning >> if (initial && sched_feat(START_DEBIT)) >> ~^~~~~~~~~~~~~~~~~~~~~~~~~~ >> @@ -1305,7 +1305,11 @@ static const_debug __maybe_unused unsigned int sysctl_sched_features = >> 0; >> #undef SCHED_FEAT >> >> +#ifdef CONFIG_SCHED_DEBUG >> #define sched_feat(x) (sysctl_sched_features & (1UL << __SCHED_FEAT_##x)) >> +#else >> +#define sched_feat(x) ((sysctl_sched_features >> __SCHED_FEAT_##x) & 1UL) >> +#endif > So this is extra ugly, for no gain? The gain is stopping a warning that clutters the output log of clang. To improve readability, one can drop the ifdef-structure and just keep the right shift version, like Nicholas suggested. This will have a (very small) impact on performance in CONFIG_SCHED_DEBUG case, but when debugging, performance is no problem anyways. > WTH does clang complain about a constant? Can't you just disable that > stupid warning? There are 2 ways to disable the warning. Either disable it for this particular occurrence, which clutters the code with #pragma's. THIS is really ugly. Or disable it globally and maybe miss some important/helpful warnings. > Also, if sysctl_sched_features is a constant, the both expressions > _should_ really result in a constant and clang should still warn about > it. No, because clang only warns if the constant is neither 1 nor 0. (These being the 'best' integer representations of booleans) > I'm really not seeing why we'd want to do this. Just fix clang to not be > stupid. >

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Re: [PATCH] sched/fair: Change sched_feat(x) in !CONFIG_SCHED_DEBUG case
by Peter Zijlstra April 20, 2018

April 20, 2018

Also, please don't cross-post with moderated lists, that's just annoying.

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Re: [PATCH] sched/fair: Change sched_feat(x) in !CONFIG_SCHED_DEBUG case
by Peter Zijlstra April 20, 2018

April 20, 2018

On Mon, Apr 16, 2018 at 10:54:26AM +0200, Philipp Klocke wrote: > This patch is motivated by the clang warning Wconstant-logical-operand, > issued when logically comparing a variable to a constant integer that is > neither 1 nor 0. It happens for sched_feat(x) when sysctl_sched_features > is constant, i.e., CONFIG_SCHED_DEBUG is not set. > > kernel/sched/fair.c:3927:14: warning: use of logical '&&' with constant operand [-Wconstant-logical-operand] > if (initial && sched_feat(START_DEBIT)) > ^ ~~~~~~~~~~~~~~~~~~~~~~~ > kernel/sched/fair.c:3927:14: note: use '&' for a bitwise operation > if (initial && sched_feat(START_DEBIT)) > ^~ > & > kernel/sched/fair.c:3927:14: note: remove constant to silence this warning > if (initial && sched_feat(START_DEBIT)) > ~^~~~~~~~~~~~~~~~~~~~~~~~~~ > @@ -1305,7 +1305,11 @@ static const_debug __maybe_unused unsigned int sysctl_sched_features = > 0; > #undef SCHED_FEAT > > +#ifdef CONFIG_SCHED_DEBUG > #define sched_feat(x) (sysctl_sched_features & (1UL << __SCHED_FEAT_##x)) > +#else > +#define sched_feat(x) ((sysctl_sched_features >> __SCHED_FEAT_##x) & 1UL) > +#endif So this is extra ugly, for no gain? WTH does clang complain about a constant? Can't you just disable that stupid warning? Also, if sysctl_sched_features is a constant, the both expressions _should_ really result in a constant and clang should still warn about it. I'm really not seeing why we'd want to do this. Just fix clang to not be stupid.

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