On Sun, Feb 11, 2018 at 09:42:09PM +0100, Ulf Magnusson wrote: > On Sun, Feb 11, 2018 at 9:29 PM, Ulf Magnusson <ulfalizer@xxxxxxxxx> wrote: > > On Sun, Feb 11, 2018 at 6:56 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: > >> Another case I mentioned before that I just want to make sure we don't > >> reintroduce the problem of getting "stuck" with a bad .config file. > >> While adding _STRONG support, I discovered the two-phase Kconfig > >> resolution that happens during the build. If you selected _STRONG with > >> a strong-capable compiler, everything was fine. If you then tried to > >> build with an older compiler, you'd get stuck since _STRONG wasn't > >> support (as detected during the first Kconfig phase) so the > >> generated/autoconf.h would never get updated with the newly selected > >> _REGULAR). I moved the Makefile analysis of available stack-protector > >> options into the second phase (i.e. after all the Kconfig runs), and > >> that worked to both unstick such configs and provide a clear message > >> early in the build about what wasn't available. > >> > >> If all this detection is getting moved up into Kconfig, I'm worried > >> we'll end up in this state again. If the answer is "you have to delete > >> autoconf.h if you change compilers", then that's fine, but it sure > >> seems unfriendly. :) > > > > Did you mean include/config/auto.conf? That's the one that gets > > included by the Makefiles. > > > > If the feature detection is moved into Kconfig, you should only need > > to rerun the configuration (make menuconfig/oldconfig/olddefconfig) if > > you change the compiler. That will update .config while taking the new > > features into account, and then the second phase during 'make' will > > update include/config/auto.conf from .config. > > > > That second Kconfig phase generates include/generated/autoconf.h and > > include/config/. The include/config/ directory implements dependencies > > between source files and Kconfig symbols by turning the symbols into > > (empty) files. When building (during the "second phase"), Kconfig > > compares .config with include/config/auto.conf to see what changed, > > and signals the changes to 'make' by touch'ing the files corresponding > > to the changed symbols. The idea is to avoid having to do a full > > rebuild whenever the configuration is changed. > > > > Check out scripts/basic/fixdep.c as well if you want to understand how it works. > > > > Cheers, > > Ulf > > By the way: > > That second phase is also a "normal" Kconfig run in the sense that it > does all the usual dependency checking stuff. Even if .config doesn't > respect dependencies, include/config/auto.conf will. So I think you > might not even need to rerun the configuration (though .config will be > out-of-date until you do). > > Cheers, > Ulf Seems you'd have to rerun the configuration, because include/config/auto.conf is only regenerated if it's older than .config. Here's the bit in the root Makefile that does it (KCONFIG_CONFIG is .config). # If .config is newer than include/config/auto.conf, someone tinkered # with it and forgot to run make oldconfig. # if auto.conf.cmd is missing then we are probably in a cleaned tree so # we execute the config step to be sure to catch updated Kconfig files include/config/%.conf: $(KCONFIG_CONFIG) include/config/auto.conf.cmd $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig silentoldconfig is a terrible name. What it actually does is run that "second phase" stuff. Pretty sure that comment lies by the way. 'make oldconfig' doesn't update include/config/auto.conf. It's probably outdated. I wonder if it would be simpler to just always run silentoldconfig when building. It's not that slow on my system: $ export ARCH=x86 SRCARCH=x86 KERNELVERSION=`make kernelversion` $ time scripts/kconfig/conf --silentoldconfig Kconfig real 0m0.167s user 0m0.162s sys 0m0.004s That'd both simplify the Makefiles, and make sure that the latest features are always used if you do feature testing in Kconfig. I don't know how strongly people feel about a few tenths of a second though. Cheers, Ulf -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
