Hi Nick, 2017-11-29 3:18 GMT+09:00 Nick Desaulniers <ndesaulniers@xxxxxxxxxx>: > Hi Masahiro, > > Thanks for merging Chris' patch, and sorry for taking so long to respond. > > On Wed, Nov 22, 2017 at 8:24 PM, Masahiro Yamada > <yamada.masahiro@xxxxxxxxxxxxx> wrote: >> Linus suggests to move compiler flag testing to Kconfig. > > Do you have an LKML link for context? https://lkml.org/lkml/2017/11/19/291 > On Wed, Nov 15, 2017 at 6:32 PM, Masahiro Yamada > <yamada.masahiro@xxxxxxxxxxxxx> wrote: >> BTW, I notice another issue. >> >> If we move clang settings before including arch Makefile, >> "ifneq ($(CROSS_COMPILE),)" comes early. >> >> Some arch Makefiles (arch/mips/Makefile, arch/blackfin/Makefile, etc.) >> set CROSS_COMPILE there if CROSS_COMPILE is not given. >> >> Then, we have a conflict between two requirements among arch. >> >> [1] arm64, powerpc use ld-option in their Makefile. >> So, clang flags must be set before inc. arch Makefile. >> [2] mips, blackfin, etc. may set CROSS_COMPILE in their Makefile. >> So, we want to reference CROSS_COMPILE only after inc. arch Makefile >> >> I have no idea how to solve it. >> >> At this moment, I guess clang is intended to support >> only limited architectures. >> >> It might be OK to be compromised here. > > I definitely find it curious that certain arch's define CROSS_COMPILE > themselves. The benefit is one less argument to supply at compile > time, but it assumes that the toolchain always has a certain prefix. > This makes sense to me when cross compiling, but seems odd when > compiling natively on that arch as the host and target. Maybe those > arch's use that convention, or simply are always cross compiled for? > > Taking a survey of all arch's currently in the kernel via `cd arch; ag > CROSS_COMPILE` and quickly eyeballing the result: > > m68k if not set > arc if not set > openrisc for some configs (openrisc/configs/or1ksim_defconfig, > openrisc/configs/simple_smp_defconfig) > blackfin if not set > hexagon for some configs (hexagon/configs/comet_defconfig) > parisc if not set > sh if not set > xtensa if not set > score always > arm for some configs (arm/configs/lpc18xx_defconfig) > h8300 if not set > mips if not set (and explicitly emptied for some configs, > mips/configs/nlm_xlr_defconfig ) > unicore32 if not set > tile if not set > > The * if not set (or not being on the list) seems correct, as the top > level Makefile will handle this correctly. Setting it for some > configs seems curious (not necessarily wrong?), Perhaps, the maintainer of those platforms may want to save one command-line argument at compile time. > emptying it/always > setting it via config sounds wrong to me, arch/mips/configs/nlm_xlr_defconfig explicitly empties it. It is just redundant because CONFIG_CROSS_COMPILE="" is the default in Kconfig. Not necessarily wrong, I think. > but maybe those hosts don't > have toolchains and must always be cross compiled for? > > For reference, this file in LLVM source defines the supported backend > targets: https://llvm.org/doxygen/Triple_8h_source.html > > Either way, it sounds like we're all set here, I guess I'm just > curious about the LKML link/context and why some configs set > CROSS_COMPILE themselves? > -- > 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 -- Best Regards Masahiro Yamada -- 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
