Hi. On Wed, Mar 3, 2021 at 6:44 AM Fangrui Song <maskray@xxxxxxxxxx> wrote: > > Reviewed-by: Fangrui Song <maskray@xxxxxxxxxx> > > Thanks for the clean-up! > --gcc-toolchain= is an obsscure way searching for GCC installation prefixes (--prefix). > The logic is complex and different for different distributions/architectures. > > If we specify --prefix= (-B) explicitly, --gcc-toolchain is not needed. I tested this, and worked for me too. Before applying this patch, could you please help me understand the logic? I checked the manual (https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-b-dir) -B<dir>, --prefix <arg>, --prefix=<arg> Add <dir> to search path for binaries and object files used implicitly --gcc-toolchain=<arg>, -gcc-toolchain <arg> Use the gcc toolchain at the given directory Hmm, this description is too concise to understand how it works... I use Ubuntu 20.10. I use distro's default clang located in /usr/bin/clang. I place my aarch64 linaro toolchain in /home/masahiro/tools/aarch64-linaro-7.5/bin/aarch64-linux-gnu-gcc, which is not in my PATH environment. >From my some experiments, clang --target=aarch64-linux-gnu -no-integrated-as \ --prefix=/home/masahiro/tools/aarch64-linaro-7.5/bin/aarch64-linux-gnu- ... works almost equivalent to PATH=/home/masahiro/tools/aarch64-linaro-7.5/bin:$PATH \ clang --target=aarch64-linux-gnu -no-integrated-as ... Then, clang will pick up aarch64-linux-gnu-as found in the search path. Is this correct? On the other hand, I could not understand what the purpose of --gcc-toolchain= is. Even if I add --gcc-toolchain=/home/masahiro/tools/aarch64-linaro-7.5, it does not make any difference, and it is completely useless. I read the comment from stephenhines: https://github.com/ClangBuiltLinux/linux/issues/78 How could --gcc-toolchain be used in a useful way? > On 2021-03-02, Nathan Chancellor wrote: > >This is not necessary anymore now that we specify '--prefix=', which > >tells clang exactly where to find the GNU cross tools. This has been > >verified with self compiled LLVM 10.0.1 and LLVM 13.0.0 as well as a > >distribution version of LLVM 11.1.0 without binutils in the LLVM > >toolchain locations. > > > >Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx> > >--- > > Makefile | 4 ---- > > 1 file changed, 4 deletions(-) > > > >diff --git a/Makefile b/Makefile > >index f9b54da2fca0..c20f0ad8be73 100644 > >--- a/Makefile > >+++ b/Makefile > >@@ -568,10 +568,6 @@ ifneq ($(CROSS_COMPILE),) > > CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%)) > > GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit)) > > CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE)) > >-GCC_TOOLCHAIN := $(realpath $(GCC_TOOLCHAIN_DIR)/..) > >-endif > >-ifneq ($(GCC_TOOLCHAIN),) > >-CLANG_FLAGS += --gcc-toolchain=$(GCC_TOOLCHAIN) > > endif > > ifneq ($(LLVM_IAS),1) > > CLANG_FLAGS += -no-integrated-as > > > >base-commit: 7a7fd0de4a9804299793e564a555a49c1fc924cb > >-- > >2.31.0.rc0.75.gec125d1bc1 > > > >-- > >You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > >To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx. > >To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20210302210646.3044738-1-nathan%40kernel.org. -- Best Regards Masahiro Yamada
