Commit 7f3a59db authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

kbuild: add infrastructure to build userspace programs 

Kbuild supports the infrastructure to build host programs, but there
was no support to build userspace programs for the target architecture
(i.e. the same architecture as the kernel).

Sam Ravnborg worked on this in 2014 (https://lkml.org/lkml/2014/7/13/154),
but it was not merged. One problem at that time was, there was no good way
to know whether $(CC) can link standalone programs. In fact, pre-built
kernel.org toolchains [1] are often used for building the kernel, but they
do not provide libc.

Now, we can handle this cleanly because the compiler capability is
evaluated at the Kconfig time. If $(CC) cannot link standalone programs,
the relevant options are hidden by 'depends on CC_CAN_LINK'.

The implementation just mimics scripts/Makefile.host

The userspace programs are compiled with the same flags as the host
programs. In addition, it uses -m32 or -m64 if it is found in
$(KBUILD_CFLAGS).

This new syntax has two usecases.

- Sample programs

  Several userspace programs under samples/ include UAPI headers
  installed in usr/include. Most of them were previously built for
  the host architecture just to use the 'hostprogs' syntax.

  However, 'make headers' always works for the target architecture.
  This caused the arch mismatch in cross-compiling. To fix this
  distortion, sample code should be built for the target architecture.

- Bpfilter

  net/bpfilter/Makefile compiles bpfilter_umh as the user mode helper,
  and embeds it into the kernel. Currently, it overrides HOSTCC with
  CC to use the 'hostprogs' syntax. This hack should go away.

[1]: https://mirrors.edge.kernel.org/pub/tools/crosstool/


Signed-off-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
Acked-by: default avatarSam Ravnborg <sam@ravnborg.org>
parent b1183b6d

Makefile

+10 −3
Original line number Diff line number Diff line
@@ -406,9 +406,12 @@ else 
HOSTCC	= gcc

HOSTCXX	= g++

endif

KBUILD_HOSTCFLAGS   := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \

		-fomit-frame-pointer -std=gnu89 $(HOST_LFS_CFLAGS) \

		$(HOSTCFLAGS)



export KBUILD_USERCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \

			      -O2 -fomit-frame-pointer -std=gnu89

export KBUILD_USERLDFLAGS :=



KBUILD_HOSTCFLAGS   := $(KBUILD_USERCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTCFLAGS)

KBUILD_HOSTCXXFLAGS := -Wall -O2 $(HOST_LFS_CFLAGS) $(HOSTCXXFLAGS)

KBUILD_HOSTLDFLAGS  := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)

KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
@@ -944,6 +947,10 @@ ifeq ($(CONFIG_RELR),y) 
LDFLAGS_vmlinux	+= --pack-dyn-relocs=relr

endif



# Align the bit size of userspace programs with the kernel

KBUILD_USERCFLAGS  += $(filter -m32 -m64, $(KBUILD_CFLAGS))

KBUILD_USERLDFLAGS += $(filter -m32 -m64, $(KBUILD_CFLAGS))



# make the checker run with the right architecture

CHECKFLAGS += --arch=$(ARCH)

scripts/Makefile.build

+6 −0
Original line number Diff line number Diff line
@@ -50,6 +50,12 @@ ifneq ($(hostprogs)$(hostcxxlibs-y)$(hostcxxlibs-m),) 
include scripts/Makefile.host

endif



# Do not include userprogs rules unless needed.

userprogs := $(sort $(userprogs))

ifneq ($(userprogs),)

include scripts/Makefile.userprogs

endif



ifndef obj

$(warning kbuild: Makefile.build is included improperly)

endif

scripts/Makefile.clean

+1 −1
Original line number Diff line number Diff line
@@ -29,7 +29,7 @@ subdir-ymn := $(addprefix $(obj)/,$(subdir-ymn)) 


__clean-files	:= $(extra-y) $(extra-m) $(extra-)       \

		   $(always) $(always-y) $(always-m) $(always-) $(targets) $(clean-files)   \

		   $(hostprogs) $(hostprogs-y) $(hostprogs-m) $(hostprogs-) \

		   $(hostprogs) $(hostprogs-y) $(hostprogs-m) $(hostprogs-) $(userprogs) \

		   $(hostcxxlibs-y) $(hostcxxlibs-m)



__clean-files   := $(filter-out $(no-clean-files), $(__clean-files))

scripts/Makefile.userprogs

0 → 100644
+45 −0
Original line number Diff line number Diff line 
# SPDX-License-Identifier: GPL-2.0-only

#

# Build userspace programs for the target system

#



# Executables compiled from a single .c file

user-csingle	:= $(foreach m, $(userprogs), $(if $($(m)-objs),,$(m)))



# Executables linked based on several .o files

user-cmulti	:= $(foreach m, $(userprogs), $(if $($(m)-objs),$(m)))



# Objects compiled from .c files

user-cobjs	:= $(sort $(foreach m, $(userprogs), $($(m)-objs)))



user-csingle	:= $(addprefix $(obj)/, $(user-csingle))

user-cmulti	:= $(addprefix $(obj)/, $(user-cmulti))

user-cobjs	:= $(addprefix $(obj)/, $(user-cobjs))



user_ccflags	= -Wp,-MMD,$(depfile) $(KBUILD_USERCFLAGS) $(userccflags) \

			$($(target-stem)-userccflags)

user_ldflags	= $(KBUILD_USERLDFLAGS) $(userldflags) $($(target-stem)-userldflags)



# Create an executable from a single .c file

quiet_cmd_user_cc_c = CC [U]  $@

      cmd_user_cc_c = $(CC) $(user_ccflags) $(user_ldflags) -o $@ $< \

		      $($(target-stem)-userldlibs)

$(user-csingle): $(obj)/%: $(src)/%.c FORCE

	$(call if_changed_dep,user_cc_c)



# Link an executable based on list of .o files

quiet_cmd_user_ld = LD [U]  $@

      cmd_user_ld = $(CC) $(user_ldflags) -o $@ \

		    $(addprefix $(obj)/, $($(target-stem)-objs)) \

		    $($(target-stem)-userldlibs)

$(user-cmulti): FORCE

	$(call if_changed,user_ld)

$(call multi_depend, $(user-cmulti), , -objs)



# Create .o file from a .c file

quiet_cmd_user_cc_o_c = CC [U]  $@

      cmd_user_cc_o_c = $(CC) $(user_ccflags) -c -o $@ $<

$(user-cobjs): $(obj)/%.o: $(src)/%.c FORCE

	$(call if_changed_dep,user_cc_o_c)



targets += $(user-csingle) $(user-cmulti) $(user-cobjs)

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