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? 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?), emptying it/always setting it via config sounds wrong to me, 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
