2018-04-14 3:11 GMT+09:00 Linus Torvalds <torva...@linux-foundation.org>: > On Fri, Apr 13, 2018 at 9:41 AM, Kees Cook <keesc...@chromium.org> wrote: >> >> How about something like this instead: > > I'd rather avoid the ifdef's in the Makefile if at all possible. > > I'd rather expose this as a Kconfig rule, and in the Kconfig just have > an entry something like this > > config STACKPROTECTOR_FLAGS > string > default "-fstack-protector-strong" if CC_STACKPROTECTOR_STRONG > default "-fstack-protector" if CC_STACKPROTECTOR > default "-fno-stack-protector" if CC_HAS_STACKPROTECTOR_NONE > default "" > > which is really simple and straightforward. In the presense of > multiple defaults, the first is picked, so this _automatically_ does > that whole priority ordering. > > And then the Makefile can just have > > KBUILD_CFLAGS += $(CONFIG_STACKPROTECTOR_FLAGS) > > which seems much simpler.
This has a minor problem. A string type symbol encloses a value with "..." like CONFIG_STACKPROTECTOR_FLAGS="-fstack-protector-strong" I think the least ugliest notation to rip off "..." is to do like follows: KBUILD_CFLAGS += $(CONFIG_STACKPROTECTOR_FLAGS:"%"=%) > It also makes more complex conditionals easier (ie different compilers > with different flags, since clang sometimes does the same thing with > another flag name), so I'd rather see this pattern in general. > > I'd also *much* rather do as much as possible at Kconfig time compared > to build time. Maybe it's just shifting the costs around, but the less > "clever" things we ask "make" to do, the better. > > I find our Makefiles an odd combination of really clean and simply > (the ones that just have "obj-$(CONFIG_X) += xyz.o" are just lovely) > and completely incomprehensible (all of our infrastructure support for > the simple stuff). > > I'd rather have more of the simple stuff in Makefiles, less of the > complex conditionals. > > Linus You showed a preference of the following, CONFIG_XYZ bool "Enable xyz" depends on $(cc-option -fxyz) CONFIG_XYZ_FLAGS string "-fxyz" if XYZ Then, in Makefile KBUILD_CFLAGS += $(CONFIG_XYZ_FLAGS:"%"=%) Users usually say y/n to a question "do you want to use xyz?" So, if you make this a general pattern, it would require one additional symbol to convert a bool symbol to a string. I think the following was your original idea. CONFIG_XYZ bool "xyz" depends on $(cc-option -fxyz) Then, in Makefile KBUILD_CFLAGS-$(CONFIG_XYZ) += -fxyz Both notations have pros/cons, but I slightly prefer the latter at the moment of time. There are some complicated cases such as stack protector flags. Your idea, config STACKPROTECTOR_FLAGS string default "-fstack-protector-strong" if CC_STACKPROTECTOR_STRONG default "-fstack-protector" if CC_STACKPROTECTOR default "-fno-stack-protector" if CC_HAS_STACKPROTECTOR_NONE default "" works fine since the first visible default is picked. In my Makefile ... stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector stackp-flags-$(CONFIG_CC_STACKPROTECTOR) := -fstack-protector stackp-flags-$(CONFIG_CC_STACKPROTECTOR_STRONG) := -fstack-protector-strong KBUILD_CFLAGS += $(stackp-flags-y) the last one is picked. IMHO, they are tied in terms of "cleanness". Perhaps I may miss something, but we will have more time to consider which approach is better. -- Best Regards Masahiro Yamada