Re: [PATCH v2 07/14] powerpc/vdso: Improve linker flags

[Sedat Dilek <sedat.dilek@gmail.com>]

On Thu, Jan 12, 2023 at 4:06 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, there
> are several warnings in the PowerPC vDSO:
>
>   clang-16: error: -Wl,-soname=linux-vdso32.so.1: 'linker' input unused [-Werror,-Wunused-command-line-argument]
>   clang-16: error: -Wl,--hash-style=both: 'linker' input unused [-Werror,-Wunused-command-line-argument]
>   clang-16: error: argument unused during compilation: '-shared' [-Werror,-Wunused-command-line-argument]
>
>   clang-16: error: argument unused during compilation: '-nostdinc' [-Werror,-Wunused-command-line-argument]
>   clang-16: error: argument unused during compilation: '-Wa,-maltivec' [-Werror,-Wunused-command-line-argument]
>
> The first group of warnings point out that linker flags were being added
> to all invocations of $(CC), even though they will only be used during
> the final vDSO link. Move those flags to ldflags-y.
>
> The second group of warnings are compiler or assembler flags that will
> be unused during linking. Filter them out from KBUILD_CFLAGS so that
> they are not used during linking.
>
> Additionally, '-z noexecstack' was added directly to the ld_and_check
> rule in commit 1d53c0192b15 ("powerpc/vdso: link with -z noexecstack")
> but now that there is a common ldflags variable, it can be moved there.
>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
> Cc: mpe@ellerman.id.au
> Cc: npiggin@gmail.com
> Cc: christophe.leroy@csgroup.eu
> Cc: linuxppc-dev@lists.ozlabs.org
> ---
>  arch/powerpc/kernel/vdso/Makefile | 18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/kernel/vdso/Makefile b/arch/powerpc/kernel/vdso/Makefile
> index 45c0cc5d34b6..4337b3aa9171 100644
> --- a/arch/powerpc/kernel/vdso/Makefile
> +++ b/arch/powerpc/kernel/vdso/Makefile
> @@ -47,13 +47,17 @@ KCOV_INSTRUMENT := n
>  UBSAN_SANITIZE := n
>  KASAN_SANITIZE := n
>
> -ccflags-y := -shared -fno-common -fno-builtin -nostdlib -Wl,--hash-style=both
> -ccflags-$(CONFIG_LD_IS_LLD) += $(call cc-option,--ld-path=$(LD),-fuse-ld=lld)
> -
> -CC32FLAGS := -Wl,-soname=linux-vdso32.so.1 -m32
> +ccflags-y := -fno-common -fno-builtin
> +ldflags-y := -Wl,--hash-style=both -nostdlib -shared -z noexecstack
> +ldflags-$(CONFIG_LD_IS_LLD) += $(call cc-option,--ld-path=$(LD),-fuse-ld=lld)
> +# Filter flags that clang will warn are unused for linking
> +ldflags-y += $(filter-out $(CC_FLAGS_FTRACE) -Wa$(comma)%, $(KBUILD_CFLAGS))
> +
> +CC32FLAGS := -m32
> +LD32FLAGS := -Wl,-soname=linux-vdso32.so.1
>  AS32FLAGS := -D__VDSO32__
>
> -CC64FLAGS := -Wl,-soname=linux-vdso64.so.1

Set CC64FLAGS := -m64 ?

> +LD64FLAGS := -Wl,-soname=linux-vdso64.so.1
>  AS64FLAGS := -D__VDSO64__
>
>  targets += vdso32.lds
> @@ -92,14 +96,14 @@ include/generated/vdso64-offsets.h: $(obj)/vdso64.so.dbg FORCE
>
>  # actual build commands
>  quiet_cmd_vdso32ld_and_check = VDSO32L $@
> -      cmd_vdso32ld_and_check = $(VDSOCC) $(c_flags) $(CC32FLAGS) -o $@ -Wl,-T$(filter %.lds,$^) $(filter %.o,$^) -z noexecstack ; $(cmd_vdso_check)
> +      cmd_vdso32ld_and_check = $(VDSOCC) $(ldflags-y) $(CC32FLAGS) $(LD32FLAGS) -o $@ -Wl,-T$(filter %.lds,$^) $(filter %.o,$^); $(cmd_vdso_check)
>  quiet_cmd_vdso32as = VDSO32A $@
>        cmd_vdso32as = $(VDSOCC) $(a_flags) $(CC32FLAGS) $(AS32FLAGS) -c -o $@ $<
>  quiet_cmd_vdso32cc = VDSO32C $@
>        cmd_vdso32cc = $(VDSOCC) $(c_flags) $(CC32FLAGS) -c -o $@ $<
>
>  quiet_cmd_vdso64ld_and_check = VDSO64L $@
> -      cmd_vdso64ld_and_check = $(VDSOCC) $(c_flags) $(CC64FLAGS) -o $@ -Wl,-T$(filter %.lds,$^) $(filter %.o,$^) -z noexecstack ; $(cmd_vdso_check)
> +      cmd_vdso64ld_and_check = $(VDSOCC) $(ldflags-y) $(CC64FLAGS) $(LD64FLAGS) -o $@ -Wl,-T$(filter %.lds,$^) $(filter %.o,$^); $(cmd_vdso_check)

If no CC64FLAGS := xxx is set, this can go?

-Sedat-

>  quiet_cmd_vdso64as = VDSO64A $@
>        cmd_vdso64as = $(VDSOCC) $(a_flags) $(CC64FLAGS) $(AS64FLAGS) -c -o $@ $<
>
>
> --
> 2.39.0
>