kselftests-bpf: add kernel BPF tests

Build and package kernel self-tests used for BPF testing, program and JIT
development. This package, together with the existing 'kmod-bpf-test', was
extensively used for past upstream Linux JIT submissions [1].

Currently this includes only 'test_verifier'; building 'test_progs' will
fail due to known endian limitations with bpftool skeletons.

[1]:https://lore.kernel.org/bpf/cover.1633392335.git.Tony.Ambardar@gmail.com

Signed-off-by: Tony Ambardar <itugrok@yahoo.com>
(cherry picked from commit 3886ea9b87c416c080078603fedea95bcc144442)

package/devel/kselftests-bpf/Makefile

@@ -0,0 +1,63 @@
+#
+# Copyright (C) 2021 Tony Ambardar <itugrok@yahoo.com>
+#
+# This is free software, licensed under the GNU General Public License v2.
+# See /LICENSE for more information.
+#
+
+include $(TOPDIR)/rules.mk
+include $(INCLUDE_DIR)/kernel.mk
+
+PKG_NAME:=kselftests-bpf
+PKG_VERSION:=$(LINUX_VERSION)
+PKG_RELEASE:=1
+PKG_MAINTAINER:=Tony Ambardar <itugrok@yahoo.com>
+
+PKG_BUILD_FLAGS:=gc-sections lto
+PKG_BUILD_PARALLEL:=1
+PKG_FLAGS:=nonshared
+
+include $(INCLUDE_DIR)/package.mk
+include $(INCLUDE_DIR)/nls.mk
+
+define Package/kselftests-bpf
+  SECTION:=devel
+  CATEGORY:=Development
+  DEPENDS:= +libelf +zlib +libpthread +librt @!IN_SDK \
+	    @KERNEL_DEBUG_FS @KERNEL_DEBUG_INFO_BTF @KERNEL_BPF_EVENTS
+  TITLE:=Linux Kernel Selftests (BPF)
+  URL:=http://www.kernel.org
+endef
+
+define Package/kselftests-bpf/description
+  kselftests-bpf is the Linux kernel BPF test suite
+endef
+
+TEST_TARGET = test_verifier
+
+MAKE_PATH:=tools/testing/selftests/bpf
+
+MAKE_VARS = \
+	ARCH="$(LINUX_KARCH)" \
+	CROSS_COMPILE="$(TARGET_CROSS)" \
+	SAN_CFLAGS="$(TARGET_CFLAGS) $(TARGET_CPPFLAGS)" \
+	LDLIBS="$(TARGET_LDFLAGS)" \
+	TOOLCHAIN_INCLUDE="$(TOOLCHAIN_DIR)/include" \
+	VMLINUX_BTF="$(LINUX_DIR)/vmlinux"
+
+MAKE_FLAGS = \
+	$(if $(findstring c,$(OPENWRT_VERBOSE)),V=1,V='') \
+	O=$(PKG_BUILD_DIR)
+
+define Build/Compile
+	+$(MAKE_VARS) \
+	$(MAKE) $(PKG_JOBS) -C $(LINUX_DIR)/$(MAKE_PATH) \
+		$(MAKE_FLAGS) $(TEST_TARGET) ;
+endef
+
+define Package/kselftests-bpf/install
+	$(INSTALL_DIR) $(1)/usr/bin
+	$(INSTALL_BIN) $(PKG_BUILD_DIR)/$(TEST_TARGET) $(1)/usr/bin/
+endef
+
+$(eval $(call BuildPackage,kselftests-bpf))