On Mon, May 26, 2025 at 04:19:53PM +0200, Nicolas Schier wrote: > On Mon, Apr 07, 2025 at 09:42:38AM +0200, Thomas Weißschuh wrote: > > 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 libc of the compiler, which may not exist. > > > > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx> > > > > --- > > 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. > > > > Also this does currently not support out-of-tree builds. > > (out-of-tree == external kmods; out-of-source == build-dir != source-dir) > > you probably meant out-of-source. I *did* mean out-of-tree. Out-of-source already works with the current patchset. It is the default setup of kunit.py. > > For that tools/include/nolibc/*.h and usr/include/*.h would need to be > > installed into the build directory. > > Out-of-source builds could be achieved by adding 'headers' as > dependency, see below. > > > --- > > Documentation/kbuild/makefiles.rst | 12 ++++++++++++ > > scripts/Makefile.userprogs | 16 +++++++++++++--- > > 2 files changed, 25 insertions(+), 3 deletions(-) > > > > diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst > > index 3b9a8bc671e2e92126857059e985d6e5b2c43fd4..f905a6f77c965311c491cfd7ab3103185af7e82e 100644 > > --- a/Documentation/kbuild/makefiles.rst > > +++ b/Documentation/kbuild/makefiles.rst > > @@ -970,6 +970,18 @@ 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 > > Bulding -> Building Ack. > > +-------------------------------- > > + > > +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 f3a7e1ef3753b54303718fae97f4b3c9d4eac07c..a1447c02b948901631098b585f5cf4d3ea383a57 100644 > > --- a/scripts/Makefile.userprogs > > +++ b/scripts/Makefile.userprogs > > @@ -16,10 +16,20 @@ user-csingle := $(addprefix $(obj)/, $(user-csingle)) > > user-cmulti := $(addprefix $(obj)/, $(user-cmulti)) > > user-cobjs := $(addprefix $(obj)/, $(user-cobjs)) > > > > +user-libgcc := $(call try-run,$(CC) -Werror $(KBUILD_USERCFLAGS) -lgcc -x c -shared /dev/null -o "$$TMP",-lgcc) > > + > > +user_nolibc_ccflags := -nostdlib -nostdinc -static -fno-ident -fno-asynchronous-unwind-tables \ > > + -ffreestanding -fno-stack-protector \ > > + -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 := $(user-libgcc) > > + > > user_ccflags = -Wp,-MMD,$(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)) > > > > # Create an executable from a single .c file > > quiet_cmd_user_cc_c = CC [U] $@ > > Adding another hunk for scripts/Makefile.userprogs would allow to build > out-of-source: > > @@ -39,5 +49,5 @@ $(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: $(src)/%.c FORCE > +$(user-cobjs): $(obj)/%.o: $(src)/%.c headers FORCE > $(call if_changed_dep,user_cc_o_c) > > But I am unsure if it is ok to add 'headers' as a build dependency for > userprogs. For me, it feels a bit odd, but I think it really makes > sense here. Currently this dependency is encoded in Kconfig. If CONFIG_HEADERS_INSTALL=y then the headers are installed in the 'prepare' phase and already available when building any userprog. To me this seems like the easier and nicer implementation.
