Userprogs are built with the regular kernel compiler $CC. A kernel compiler does not necessarily contain a libc which is required for a normal userspace application. However the kernel tree does contain a minimal libc implementation "nolibc" which can be used to build userspace applications.
Introduce support to build userprogs against nolibc instead of the default C of the compiler, which may not exist. Signed-off-by: Thomas Weißschuh <thomas.weisssc...@linutronix.de> --- This could probably be moved out of the generic kbuild makefiles. I think the ergonimics would suffer and this functionality could be used by other users of userprogs. --- Documentation/kbuild/makefiles.rst | 12 ++++++++++++ scripts/Makefile.userprogs | 14 +++++++++++--- 2 files changed, 23 insertions(+), 3 deletions(-) diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst index d36519f194dc0d18b72a6f3ce7f3649f7c1b5637..cb859dc58b579def4995a5aa2efb45ab4ba3c93f 100644 --- a/Documentation/kbuild/makefiles.rst +++ b/Documentation/kbuild/makefiles.rst @@ -959,6 +959,18 @@ When linking bpfilter_umh, it will be passed the extra option -static. From command line, :ref:`USERCFLAGS and USERLDFLAGS <userkbuildflags>` will also be used. +Bulding userprogs against nolibc +-------------------------------- + +Not all kernel toolchains provide a libc. +Simple userprogs can be built against a very simple libc call "nolibc" provided +by the kernel source tree. + +Example:: + + # lib/kunit/Makefile + uapi-preinit-nolibc := $(CONFIG_ARCH_HAS_NOLIBC) + When userspace programs are actually built ------------------------------------------ diff --git a/scripts/Makefile.userprogs b/scripts/Makefile.userprogs index debbf083bcfa01c89c204a322a1b17e2bdbe95a1..e94f3f2250f531dadbe00f5f5ee6f780bee22487 100644 --- a/scripts/Makefile.userprogs +++ b/scripts/Makefile.userprogs @@ -16,10 +16,18 @@ user-csingle := $(addprefix $(obj)/, $(user-csingle)) user-cmulti := $(addprefix $(obj)/, $(user-cmulti)) user-cobjs := $(addprefix $(obj)/, $(user-cobjs)) +user_nolibc_ccflags := -nostdlib -nostdinc -static -fno-ident -fno-asynchronous-unwind-tables \ + -ffreestanding $(call cc-option,-mstack-protector-guard=global) \ + -isystem $(objtree)/usr/include -include $(srctree)/tools/include/nolibc/nolibc.h -isystem $(srctree)/tools/include/nolibc/ +user_nolibc_ldflags := -nostdlib -nostdinc -static +user_nolibc_ldlibs := $(call cc-option,-lgcc) + user_ccflags = -Wp,-MMD,$(depfile) $(KBUILD_USERCFLAGS) $(userccflags) \ - $($(target-stem)-userccflags) -user_ldflags = $(KBUILD_USERLDFLAGS) $(userldflags) $($(target-stem)-userldflags) -user_ldlibs = $(userldlibs) $($(target-stem)-userldlibs) + $($(target-stem)-userccflags) $(if $($(target-stem)-nolibc),$(user_nolibc_ccflags)) +user_ldflags = $(KBUILD_USERLDFLAGS) $(userldflags) $($(target-stem)-userldflags) \ + $(if $($(target-stem)-nolibc),$(user_nolibc_ldflags)) +user_ldlibs = $(userldlibs) $($(target-stem)-userldlibs) \ + $(if $($(target-stem)-nolibc),$(user_nolibc_ldlibs)) ifdef CONFIG_WERROR KBUILD_USERCFLAGS += -Werror -- 2.48.1
