bpfilter: switch to CC from HOSTCC

check that CC can build executables and use that compiler instead of HOSTCC
Suggested-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Makefile

@@ -510,6 +510,11 @@ ifeq ($(call shell-cached,$(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC) $
   KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
 endif
 
+ifeq ($(call shell-cached,$(CONFIG_SHELL) $(srctree)/scripts/cc-can-link.sh $(CC)), y)
+  CC_CAN_LINK := y
+  export CC_CAN_LINK
+endif
+
 ifeq ($(config-targets),1)
 # ===========================================================================
 # *config targets only - make sure prerequisites are updated, and descend

net/Makefile

@@ -20,7 +20,11 @@ obj-$(CONFIG_TLS)		+= tls/
 obj-$(CONFIG_XFRM)		+= xfrm/
 obj-$(CONFIG_UNIX)		+= unix/
 obj-$(CONFIG_NET)		+= ipv6/
+ifneq ($(CC_CAN_LINK),y)
+$(warning CC cannot link executables. Skipping bpfilter.)
+else
 obj-$(CONFIG_BPFILTER)		+= bpfilter/
+endif
 obj-$(CONFIG_PACKET)		+= packet/
 obj-$(CONFIG_NET_KEY)		+= key/
 obj-$(CONFIG_BRIDGE)		+= bridge/

net/bpfilter/Makefile

@@ -6,6 +6,8 @@
 hostprogs-y := bpfilter_umh
 bpfilter_umh-objs := main.o
 HOSTCFLAGS += -I. -Itools/include/ -Itools/include/uapi
+HOSTCC := $(CC)
+
 ifeq ($(CONFIG_BPFILTER_UMH), y)
 # builtin bpfilter_umh should be compiled with -static
 # since rootfs isn't mounted at the time of __init

scripts/cc-can-link.sh

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+cat << "END" | $@ -x c - -o /dev/null >/dev/null 2>&1 && echo "y"
+#include <stdio.h>
+int main(void)
+{
+	printf("");
+	return 0;
+}
+END