sched_ext: Improve cross-compilation support in Makefile

Modify the tools/sched_ext/Makefile to better handle cross-compilation
environments by:

1. Fix host tools build directory structure by separating obj/ from output
   (HOST_BUILD_DIR now points to $(OBJ_DIR)/host/obj)
2. Properly propagate CROSS_COMPILE to libbpf sub-make invocation
3. Add missing $(HOST_BPFOBJ) build rule with proper host toolchain flags
   (ARCH=, CROSS_COMPILE=, explicit HOSTCC/HOSTLD)
4. Consistently quote $(HOSTCC) in bpftool build rule
5. Change LDFLAGS assignment to += to allow external extensions

The changes ensure proper cross-compilation behavior while maintaining
backward compatibility with native builds. Host tools are now correctly
built with the host toolchain while target binaries use the cross-toolchain.

Signed-off-by: yangsonghua <yangsonghua@lixiang.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/tools/sched_ext/Makefile b/tools/sched_ext/Makefile
index ca3815e572d8d2030e61663204eb7e46e36d1e3b..d68780e2e03d667e23092461d6bd7a376edb28ae 100644 (file)
--- a/tools/sched_ext/Makefile
+++ b/tools/sched_ext/Makefile
@@ -61,8 +61,8 @@ SCXOBJ_DIR := $(OBJ_DIR)/sched_ext
 BINDIR := $(OUTPUT_DIR)/bin
 BPFOBJ := $(BPFOBJ_DIR)/libbpf.a
 ifneq ($(CROSS_COMPILE),)
-HOST_BUILD_DIR         := $(OBJ_DIR)/host
-HOST_OUTPUT_DIR        := host-tools
+HOST_BUILD_DIR         := $(OBJ_DIR)/host/obj
+HOST_OUTPUT_DIR        := $(OBJ_DIR)/host
 HOST_INCLUDE_DIR       := $(HOST_OUTPUT_DIR)/include
 else
 HOST_BUILD_DIR         := $(OBJ_DIR)
@@ -98,7 +98,7 @@ ifneq ($(LLVM),)
 CFLAGS += -Wno-unused-command-line-argument
 endif
 
-LDFLAGS = -lelf -lz -lpthread
+LDFLAGS += -lelf -lz -lpthread
 
 IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null |                         \
                        grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
@@ -136,14 +136,25 @@ $(MAKE_DIRS):
 $(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)                     \
           $(APIDIR)/linux/bpf.h                                                \
           | $(OBJ_DIR)/libbpf
-       $(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(OBJ_DIR)/libbpf/    \
+       $(Q)$(MAKE) $(submake_extras) CROSS_COMPILE=$(CROSS_COMPILE)            \
+                   -C $(BPFDIR) OUTPUT=$(OBJ_DIR)/libbpf/                      \
                    EXTRA_CFLAGS='-g -O0 -fPIC'                                 \
+                   LDFLAGS="$(LDFLAGS)"                                        \
                    DESTDIR=$(OUTPUT_DIR) prefix= all install_headers
 
+$(HOST_BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)                \
+          $(APIDIR)/linux/bpf.h                                                \
+          | $(HOST_BUILD_DIR)/libbpf
+       $(Q)$(MAKE) $(submake_extras) -C $(BPFDIR)                              \
+                   OUTPUT=$(HOST_BUILD_DIR)/libbpf/                            \
+                   ARCH= CROSS_COMPILE= CC="$(HOSTCC)" LD=$(HOSTLD)            \
+                   EXTRA_CFLAGS='-g -O0 -fPIC'                                 \
+                   DESTDIR=$(HOST_OUTPUT_DIR) prefix= all install_headers
+
 $(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile)    \
                    $(HOST_BPFOBJ) | $(HOST_BUILD_DIR)/bpftool
        $(Q)$(MAKE) $(submake_extras)  -C $(BPFTOOLDIR)                         \
-                   ARCH= CROSS_COMPILE= CC=$(HOSTCC) LD=$(HOSTLD)              \
+                   ARCH= CROSS_COMPILE= CC="$(HOSTCC)" LD=$(HOSTLD)            \
                    EXTRA_CFLAGS='-g -O0'                                       \
                    OUTPUT=$(HOST_BUILD_DIR)/bpftool/                           \
                    LIBBPF_OUTPUT=$(HOST_BUILD_DIR)/libbpf/                     \
@@ -185,7 +196,7 @@ $(addprefix $(BINDIR)/,$(c-sched-targets)): \
                $(SCX_COMMON_DEPS)
        $(eval sched=$(notdir $@))
        $(CC) $(CFLAGS) -c $(sched).c -o $(SCXOBJ_DIR)/$(sched).o
-       $(CC) -o $@ $(SCXOBJ_DIR)/$(sched).o $(HOST_BPFOBJ) $(LDFLAGS)
+       $(CC) -o $@ $(SCXOBJ_DIR)/$(sched).o $(BPFOBJ) $(LDFLAGS)
 
 $(c-sched-targets): %: $(BINDIR)/%