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

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Date:   Tue, 1 Feb 2022 14:03:08 -0800
From:   Fāng-ruì Sòng <maskray@...gle.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Elliot Berman <quic_eberman@...cinc.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        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 1:38 PM Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>
> 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:

s/Clang 13+/Clang/.

Clang has been detecting GCC installation for a long time.
Clang 13 just improved some detection, but may not be worth mentioning
in the message.

> > $ 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>

LGTM.

Reviewed-by: Fangrui Song <maskray@...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



-- 
宋方睿