linux-kernel - Re: [PATCH v3] kbuild: Add environment variables for userprogs flags

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Date:   Tue, 1 Feb 2022 13:38:06 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Elliot Berman <quic_eberman@...cinc.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Fangrui Song <maskray@...gle.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nathan Chancellor <nathan@...nel.org>,
        Matthias Maennich <maennich@...gle.com>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v3] kbuild: Add environment variables for userprogs flags

On Tue, Feb 1, 2022 at 1:36 PM Elliot Berman <quic_eberman@...cinc.com> wrote:
>
> Allow additional arguments be passed to userprogs compilation.
> Reproducible clang builds need to provide a sysroot and gcc path to
> ensure same toolchain is used across hosts. KCFLAGS is not currently

^ ensure the same (maybe Masahiro can fix that up locally when applying)

> used for any user programs compilation, so add new USERCFLAGS and
> USERLDFLAGS which serves similar purpose as HOSTCFLAGS/HOSTLDFLAGS.
>
> Clang 13+ might detect GCC installation on hosts which have it installed
> to a default location in /. With addition of these environment
> variables, you can specify flags such as:
>
> $ make USERCFLAGS=--sysroot=/path/to/sysroot
>
> This can also be used to specify different sysroots such as musl or
> bionic which may be installed on the host in paths that the compiler
> may not search by default.
>
> Signed-off-by: Elliot Berman <quic_eberman@...cinc.com>

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>
> Changes since v2:
>  - Incorporated Nick's suggestions:
>    - Addressed docs and commit text comments
>    - Introduced KBUILD_USERHOSTCFLAGS as suggested
>
>  Documentation/kbuild/kbuild.rst    | 11 +++++++++++
>  Documentation/kbuild/makefiles.rst |  2 ++
>  Makefile                           | 10 ++++++----
>  init/Kconfig                       |  8 ++++----
>  usr/include/Makefile               |  3 +++
>  5 files changed, 26 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
> index 2d1fc03d346e..ef19b9c13523 100644
> --- a/Documentation/kbuild/kbuild.rst
> +++ b/Documentation/kbuild/kbuild.rst
> @@ -77,6 +77,17 @@ HOSTLDLIBS
>  ----------
>  Additional libraries to link against when building host programs.
>
> +.. _userkbuildflags:
> +
> +USERCFLAGS
> +----------
> +Additional options used for $(CC) when compiling userprogs.
> +
> +USERLDFLAGS
> +-----------
> +Additional options used for $(LD) when linking userprogs. userprogs are linked
> +with CC, so $(USERLDFLAGS) should include "-Wl," prefix as applicable.
> +
>  KBUILD_KCONFIG
>  --------------
>  Set the top-level Kconfig file to the value of this environment
> diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst
> index b008b90b92c9..11a296e52d68 100644
> --- a/Documentation/kbuild/makefiles.rst
> +++ b/Documentation/kbuild/makefiles.rst
> @@ -982,6 +982,8 @@ The syntax is quite similar. The difference is to use "userprogs" instead of
>
>         When linking bpfilter_umh, it will be passed the extra option -static.
>
> +       From command line, :ref:`USERCFLAGS and USERLDFLAGS <userkbuildflags>` will also be used.
> +
>  5.4 When userspace programs are actually built
>  ----------------------------------------------
>
> diff --git a/Makefile b/Makefile
> index 45278d508d81..1d0172449355 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -431,11 +431,12 @@ HOSTCC    = gcc
>  HOSTCXX        = g++
>  endif
>
> -export KBUILD_USERCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \
> -                             -O2 -fomit-frame-pointer -std=gnu89
> -export KBUILD_USERLDFLAGS :=
> +KBUILD_USERHOSTCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \
> +                        -O2 -fomit-frame-pointer -std=gnu89
> +KBUILD_USERCFLAGS  := $(KBUILD_USERHOSTCFLAGS) $(USERCFLAGS)
> +KBUILD_USERLDFLAGS := $(USERLDFLAGS)
>
> -KBUILD_HOSTCFLAGS   := $(KBUILD_USERCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTCFLAGS)
> +KBUILD_HOSTCFLAGS   := $(KBUILD_USERHOSTCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTCFLAGS)
>  KBUILD_HOSTCXXFLAGS := -Wall -O2 $(HOST_LFS_CFLAGS) $(HOSTCXXFLAGS)
>  KBUILD_HOSTLDFLAGS  := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)
>  KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
> @@ -530,6 +531,7 @@ export CPP AR NM STRIP OBJCOPY OBJDUMP READELF PAHOLE RESOLVE_BTFIDS LEX YACC AW
>  export PERL PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
>  export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ ZSTD
>  export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE
> +export KBUILD_USERCFLAGS KBUILD_USERLDFLAGS
>
>  export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS
>  export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
> diff --git a/init/Kconfig b/init/Kconfig
> index f2ae41e6717f..164706c38e8b 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -62,13 +62,13 @@ config LLD_VERSION
>
>  config CC_CAN_LINK
>         bool
> -       default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag)) if 64BIT
> -       default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag))
> +       default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag)) if 64BIT
> +       default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag))
>
>  config CC_CAN_LINK_STATIC
>         bool
> -       default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag) -static) if 64BIT
> -       default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag) -static)
> +       default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag) -static) if 64BIT
> +       default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag) -static)
>
>  config CC_HAS_ASM_GOTO
>         def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
> diff --git a/usr/include/Makefile b/usr/include/Makefile
> index 1c2ae1368079..0322e567dc1e 100644
> --- a/usr/include/Makefile
> +++ b/usr/include/Makefile
> @@ -12,6 +12,9 @@ UAPI_CFLAGS := -std=c90 -Wall -Werror=implicit-function-declaration
>  # It is here just because CONFIG_CC_CAN_LINK is tested with -m32 or -m64.
>  UAPI_CFLAGS += $(filter -m32 -m64, $(KBUILD_CFLAGS))
>
> +# USERCFLAGS might contain sysroot location for CC.
> +UAPI_CFLAGS += $(USERCFLAGS)
> +
>  override c_flags = $(UAPI_CFLAGS) -Wp,-MMD,$(depfile) -I$(objtree)/usr/include
>
>  # The following are excluded for now because they fail to build.
> --
> 2.25.1
>


-- 
Thanks,
~Nick Desaulniers