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

From: Nick Desaulniers
Date: Tue Feb 01 2022 - 16:38:23 EST

On Tue, Feb 1, 2022 at 1:36 PM Elliot Berman <quic_eberman@xxxxxxxxxxx> 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@xxxxxxxxxxx>

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>

> ---
>
> 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