On Wed, Jan 24, 2024 at 8:00 AM Nathan Chancellor <nathan@xxxxxxxxxx> wrote:
>
> The kernel builds with -fno-PIE, so commit 883354afbc10 ("um: link
> vmlinux with -no-pie") added the compiler linker flag '-no-pie' via
> cc-option because '-no-pie' was only supported in GCC 6.1.0 and newer.
>
> While this works for GCC, this does not work for clang because cc-option
> uses '-c', which stops the pipeline right before linking, so '-no-pie'
> is unconsumed and clang warns, causing cc-option to fail just as it
> would if the option was entirely unsupported:
>
> $ clang -Werror -no-pie -c -o /dev/null-x c /dev/null
A nit. A missing space in-between.
I fixed "/dev/null-x" to "/dev/null -x"
when I applied the patch.
> clang-16: error: argument unused during compilation: '-no-pie' [-Werror,-Wunused-command-line-argument]
>
> A recent version of clang exposes this because it generates a relocation
> under '-mcmodel=large' that is not supported in PIE mode:
>
> /usr/sbin/ld: init/main.o: relocation R_X86_64_32 against symbol `saved_command_line' can not be used when making a PIE object; recompile with -fPIE
> /usr/sbin/ld: failed to set dynamic section sizes: bad value
> clang: error: linker command failed with exit code 1 (use -v to see invocation)
>
> Remove the cc-option check altogether. It is wasteful to invoke the
> compiler to check for '-no-pie' because only one supported compiler
> version does not support it, GCC 5.x (as it is supported with the
> minimum version of clang and GCC 6.1.0+). Use a combination of the
> gcc-min-version macro and CONFIG_CC_IS_CLANG to unconditionally add
> '-no-pie' with CONFIG_LD_SCRIPT_DYN=y, so that it is enabled with all
> compilers that support this. Furthermore, using gcc-min-version can help
> turn this back into
>
> LINK-$(CONFIG_LD_SCRIPT_DYN) += -no-pie
>
> when the minimum version of GCC is bumped past 6.1.0.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Closes: https://github.com/ClangBuiltLinux/linux/issues/1982
> Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> ---
> arch/um/Makefile | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/um/Makefile b/arch/um/Makefile
> index 82f05f250634..34957dcb88b9 100644
> --- a/arch/um/Makefile
> +++ b/arch/um/Makefile
> @@ -115,7 +115,9 @@ archprepare:
> $(Q)$(MAKE) $(build)=$(HOST_DIR)/um include/generated/user_constants.h
>
> LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static
> -LINK-$(CONFIG_LD_SCRIPT_DYN) += $(call cc-option, -no-pie)
> +ifdef CONFIG_LD_SCRIPT_DYN
> +LINK-$(call gcc-min-version, 60100)$(CONFIG_CC_IS_CLANG) += -no-pie
> +endif
> LINK-$(CONFIG_LD_SCRIPT_DYN_RPATH) += -Wl,-rpath,/lib
>
> CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \
>
> --
> 2.43.0
>
--
Best Regards
Masahiro Yamada
