On Fri, Aug 12, 2016 at 10:23:34PM +0200, Greg KH wrote: > On Fri, Aug 12, 2016 at 07:04:52PM +0200, Luis R. Rodriguez wrote: > > Alright, how's this new description: > > > > diff --git a/init/Kconfig b/init/Kconfig > > index cac3f096050d..73e4890c24c4 100644 > > --- a/init/Kconfig > > +++ b/init/Kconfig > > @@ -53,6 +53,34 @@ config CROSS_COMPILE > > need to set this unless you want the configured kernel build > > directory to select the cross-compiler automatically. > > > > +config BUILD_AVOID_BITROT > > + bool "Always force building specially annotated targets" > > + default n > > + help > > + If enabled then the the special table-* Makefile targets will always > > + be forced to be compiled even if their respective CONFIG_ option has > > + been disabled, but its objects will only be linked in if the same > > + respective CONFIG_ option has been enabled. This helps avoid code > > + bit rot issues, use for these targets should be carefully considred > > + by maintainers. You can safely enable this option at the expense of > > + increasing compile time. Enabling this option helps avoid code bit > > + rot by taking advantage of the facilities provided and enabled by > > + using linker tables documented under: > > As a kernel developer I have _no_ idea what this is trying to say at > all, sorry. Hmm, wow OK, sorry, and I thought I was being too verbose... OK so first, linker tables allow for the ability to help simplify initialization sequences so that you no longer have to add the respective static inline in header files to do nothing, instead you simply get your init routine for your feature pegged into the linker table or not at link time. If enabling your feature does not require structural changes, you could then safely enable compiling this feature all the time, and only allow linking when the feature was enabled. We don't have an easy way to express this in our build system, the new targets added lets you accomplish this. > What is a "specially annotated target"? The ones listed below, table-obj-y and table-lib-y > Who is forcing it to be built? It would be up to maintainers for each subsystem/feature to decide if they want to use the new targets or not within their subsystem. > What does it mean if it isn't built? If you have CONFIG_BUILD_AVOID_BITROT enabled and some code using the special targets do not get built it means the dependencies it has were not met. > > + > > + include/linux/tables.h > > + > > + The special targets supported are: > > + > > + o table-obj-y > > + o table-lib-y > > What does this mean to me as a developer? It mean you can count on a bit more build test coverage by CONFIG_BUILD_AVOID_BITROT users. Using table-obj-y is functionally equivalent to doing: extra-y += foo.o obj-y += foo.o The above new targets are just short hand annotations for the same. We could actually use another shorthand prefix other than table-, however linker tables help making more of these type of targets possible. For instance, on initialiation sequences you no longer have to add each line for each feature onto a set routine, rather you just get the initialization routine linked in or not. This lets us avoid cluttering C code and header code with #idefs, and as a side consequences also allows more targets to be compiled without implicating functionality. As a developer you should take care to to use table-obj-y, or table-lib-y only if you are certain the target does not require structural changes. > What does it mean to a user > who wants to figure out if it should be enabled or not? It depends on their build system capability and their goals. If they wish to be able to report build bugs and have a decent build system they can enable this. Otherwise they should disable it. > > + Say Y if you have a decent build machine and would like to help test > > + building code for more subsystems. Say N if you do you not have a > > + good build machine or only want to compile what you've enabled for > > + your kernel. > > How does this test different subsystems? By enabling this feature you compile kconfig symbols that typically are disabled by most users and which have been identified by maintainers as needing more build testing love. The extra kconfig symbols built are only built if the dependencies for them are met. Maintainers for subsystems would have to identify if they have key pieces of software that typically get disabled, and that enabling them would not incur or require structural changes, which can use more build test love. > How does disabling it not test them? By disabling this feature you only compile kconfig symbols you have enabled for your kernel. > Why would I care either way? You would care if you aware of certain kconfig symbols that do not get much build test love. > > + > > + Enabling this option never increases the size of your kernel. > > Then what does it do? Just burn electricity for no reason? It enables maintainers to annotate through the build system certain kconfig symbol which should be built if CONFIG_BUILD_AVOID_BITROT is enabled and its symbol dependencies are met. Luis -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
