[PATCH bpf-next 7/8] samples: bpf: add makefile.prog for separate CC build

[Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>]

The HOSTCC is supposed to build binaries and tools running on the host
afterwards, in order to simplify build or so, like "fixdep" or else.
In case of cross compiling "fixdep" is executed on host when the rest
samples should run on target arch. In order to build binaries for
target arch with CC and tools running on host with HOSTCC, lets add
Makefile.prog for simplicity, having definition and routines similar
to ones, used in script/Makefile.host. That allows later add
cross-compilation to samples/bpf with minimum changes.

Makefile.prog contains only stuff needed for samples/bpf, potentially
can be reused and extended for other prog sets later and now needed
only for unblocking tricky samples/bpf cross compilation.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
---
 samples/bpf/Makefile.prog | 77 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 samples/bpf/Makefile.prog

diff --git a/samples/bpf/Makefile.prog b/samples/bpf/Makefile.prog
new file mode 100644
index 000000000000..1d138bc21dd4
--- /dev/null
+++ b/samples/bpf/Makefile.prog
@@ -0,0 +1,77 @@
+# SPDX-License-Identifier: GPL-2.0
+# ==========================================================================
+# Building binaries on the host system
+# Binaries are not used during the compilation of the kernel, and intendent to
+# be build for target board, target board can be host ofc. Added to build
+# binaries to run not on host system.
+#
+# Only C is supported, but can be extended for C++.
+#
+# Sample syntax (see Documentation/kbuild/makefiles.rst for reference)
+# progs-y := xdpsock_example
+# Will compile xdpsock_example.c and create an executable named xdpsock_example
+#
+# progs-y    := xdpsock
+# xdpsock-objs := xdpsock_user.o xdpsock_user2.o
+# Will compile xdpsock.c and xdpsock.c, and then link the executable
+# xdpsock, based on xdpsock_user.o and xdpsock_user2.o
+#
+# Inherited from scripts/Makefile.host
+#
+__progs := $(sort $(progs-y))
+
+# C code
+# Executables compiled from a single .c file
+prog-csingle	:= $(foreach m,$(__progs), \
+			$(if $($(m)-objs)$($(m)-cxxobjs),,$(m)))
+
+# C executables linked based on several .o files
+prog-cmulti	:= $(foreach m,$(__progs),\
+		   $(if $($(m)-cxxobjs),,$(if $($(m)-objs),$(m))))
+
+# Object (.o) files compiled from .c files
+prog-cobjs	:= $(sort $(foreach m,$(__progs),$($(m)-objs)))
+
+prog-csingle	:= $(addprefix $(obj)/,$(prog-csingle))
+prog-cmulti	:= $(addprefix $(obj)/,$(prog-cmulti))
+prog-cobjs	:= $(addprefix $(obj)/,$(prog-cobjs))
+
+#####
+# Handle options to gcc. Support building with separate output directory
+
+_progc_flags   = $(PROGS_CFLAGS) \
+                 $(PROGCFLAGS_$(basetarget).o)
+
+# $(objtree)/$(obj) for including generated headers from checkin source files
+ifeq ($(KBUILD_EXTMOD),)
+ifdef building_out_of_srctree
+_progc_flags   += -I $(objtree)/$(obj)
+endif
+endif
+
+progc_flags    = -Wp,-MD,$(depfile) $(_progc_flags)
+
+# Create executable from a single .c file
+# prog-csingle -> Executable
+quiet_cmd_prog-csingle 	= CC  $@
+      cmd_prog-csingle	= $(CC) $(progc_flags) $(PROGS_LDFLAGS) -o $@ $< \
+		$(PROGS_LDLIBS) $(PROGLDLIBS_$(@F))
+$(prog-csingle): $(obj)/%: $(src)/%.c FORCE
+	$(call if_changed_dep,prog-csingle)
+
+# Link an executable based on list of .o files, all plain c
+# prog-cmulti -> executable
+quiet_cmd_prog-cmulti	= LD  $@
+      cmd_prog-cmulti	= $(CC) $(progc_flags) $(PROGS_LDFLAGS) -o $@ \
+			  $(addprefix $(obj)/,$($(@F)-objs)) \
+			  $(PROGS_LDLIBS) $(PROGLDLIBS_$(@F))
+$(prog-cmulti): $(prog-cobjs) FORCE
+	$(call if_changed,prog-cmulti)
+$(call multi_depend, $(prog-cmulti), , -objs)
+
+# Create .o file from a single .c file
+# prog-cobjs -> .o
+quiet_cmd_prog-cobjs	= CC  $@
+      cmd_prog-cobjs	= $(CC) $(progc_flags) -c -o $@ $<
+$(prog-cobjs): $(obj)/%.o: $(src)/%.c FORCE
+	$(call if_changed_dep,prog-cobjs)
-- 
2.17.1