[PW_SID:970692] kunit: Introduce UAPI testing framework

Documentation/dev-tools/kunit/api/index.rst

@@ -9,6 +9,7 @@ API Reference
 	test
 	resource
 	functionredirection
+	uapi
 	clk
 	of
 	platformdevice
@@ -32,6 +33,10 @@ Documentation/dev-tools/kunit/api/functionredirection.rst
 
  - Documents the KUnit Function Redirection API
 
+Documentation/dev-tools/kunit/api/uapi.rst
+
+ - Documents the KUnit Userspace testing API
+
 Driver KUnit API
 ================
 

Documentation/dev-tools/kunit/api/uapi.rst

@@ -0,0 +1,12 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==================
+Userspace Test API
+==================
+
+This file documents all of the userspace testing API.
+Userspace tests should be built as :ref:`userprogs <kbuild_userprogs>` and included into the test
+module or kernel as :ref:`blobs <kbuild_blobs>`.
+
+.. kernel-doc:: include/kunit/uapi.h
+   :internal:

Documentation/kbuild/makefiles.rst

@@ -525,8 +525,8 @@ otherwise the command line check will fail, and the target will
 always be built.
 
 If the target is already listed in the recognized syntax such as
-obj-y/m, lib-y/m, extra-y/m, always-y/m, hostprogs, userprogs, Kbuild
-automatically adds it to $(targets). Otherwise, the target must be
+obj-y/m, lib-y/m, extra-y/m, always-y/m, hostprogs, userprogs, blobs,
+Kbuild automatically adds it to $(targets). Otherwise, the target must be
 explicitly added to $(targets).
 
 Assignments to $(targets) are without $(obj)/ prefix. if_changed may be
@@ -891,6 +891,8 @@ This is possible in two ways:
     This will tell kbuild to build lxdialog even if not referenced in
     any rule.
 
+.. _kbuild_userprogs:
+
 Userspace Program support
 =========================
 
@@ -974,6 +976,19 @@ When linking bpfilter_umh, it will be passed the extra option -static.
 
 From command line, :ref:`USERCFLAGS and USERLDFLAGS <userkbuildflags>` will also be used.
 
+Building userprogs against nolibc
+---------------------------------
+
+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.
+This requires ``CONFIG_HEADERS_INSTALL=y``.
+
+Example::
+
+  # lib/kunit/Makefile
+  uapi-preinit-nolibc := $(CONFIG_ARCH_HAS_NOLIBC)
+
 When userspace programs are actually built
 ------------------------------------------
 
@@ -1004,6 +1019,25 @@ There are two ways to do this.
     This will tell Kbuild to build binderfs_example when it visits this
     Makefile.
 
+.. _kbuild_blobs:
+
+Blob framework
+==============
+
+Kbuild supports wrapping source or generated files into object files which are linked
+into the kernel and then accessed at runtime through ``include/linux/blob.h``.
+
+Example::
+
+  obj-m := some-module.o
+  userprogs := some-userprog
+  blobs := some-userprog.blob.o
+  some-userprog.blob-symbol := some_userprog
+  some-module-y += some-userprog.blob.o
+
+Kbuild will build the :ref:`userprog <kbuild_userprogs>` ``some-userprog`` and
+link it into ``some-module`` from where it can be accessed as ``BLOB(some_userprog)``.
+
 Kbuild clean infrastructure
 ===========================
 

MAINTAINERS

@@ -13063,11 +13063,13 @@ Q:	https://patchwork.kernel.org/project/linux-kbuild/list/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git
 F:	Documentation/kbuild/
 F:	Makefile
+F:	include/linux/blob.h
 F:	scripts/*vmlinux*
 F:	scripts/Kbuild*
 F:	scripts/Makefile*
 F:	scripts/bash-completion/
 F:	scripts/basic/
+F:	scripts/blob-wrap.c
 F:	scripts/clang-tools/
 F:	scripts/dummy-tools/
 F:	scripts/include/

Makefile

@@ -1129,9 +1129,10 @@ ifneq ($(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS),)
 LDFLAGS_vmlinux	+= --emit-relocs --discard-none
 endif
 
-# Align the bit size of userspace programs with the kernel
-KBUILD_USERCFLAGS  += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
-KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
+# Align the bit size, byte order and architecture of userspace programs with the kernel
+USERFLAGS_FROM_KERNEL := -m32 -m64 -mlittle-endian -mbig-endian --target=% -march=% -mabi=%
+KBUILD_USERCFLAGS  += $(filter $(USERFLAGS_FROM_KERNEL), $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
+KBUILD_USERLDFLAGS += $(filter $(USERFLAGS_FROM_KERNEL), $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
 
 # userspace programs are linked via the compiler, use the correct linker
 ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_LD_IS_LLD),yy)

include/kunit/uapi.h

@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * KUnit Userspace testing API.
+ *
+ * Copyright (C) 2025, Linutronix GmbH.
+ * Author: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
+ */
+
+#ifndef _KUNIT_UAPI_H
+#define _KUNIT_UAPI_H
+
+struct blob;
+struct kunit;
+
+/**
+ * kunit_uapi_run_kselftest() - Run a userspace kselftest as part of kunit
+ * @test: The test context object.
+ * @executable: kselftest executable to run
+ *
+ * Runs the kselftest and forwards its TAP output and exit status to kunit.
+ */
+void kunit_uapi_run_kselftest(struct kunit *test, const struct blob *executable);
+
+#endif /* _KUNIT_UAPI_H */

include/linux/blob.h

@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Linkable blob API.
+ *
+ * Copyright (C) 2025, Linutronix GmbH.
+ * Author: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
+ */
+
+#ifndef _LINUX_BLOB_H
+#define _LINUX_BLOB_H
+
+#include <linux/args.h>
+#include <linux/types.h>
+
+struct blob {
+	const char *const path;
+	const u8 *data;
+	const u8 *end;
+};
+
+#define BLOB(_symbol)	({					\
+	extern const struct blob CONCATENATE(__blob_, _symbol);	\
+	&CONCATENATE(__blob_, _symbol);				\
+})
+
+static inline size_t blob_size(const struct blob *blob)
+{
+	return blob->end - blob->data;
+}
+
+#endif /* _LINUX_BLOB_H */

init/Kconfig

@@ -87,6 +87,13 @@ config CC_CAN_LINK
 	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag)) if 64BIT
 	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag))
 
+config CC_CAN_LINK_STATIC
+	bool
+	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag) -static) if 64BIT
+	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag) -static)
+
+source "tools/include/nolibc/Kconfig.nolibc"
+
 # Fixed in GCC 14, 13.3, 12.4 and 11.5
 # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113921
 config GCC_ASM_GOTO_OUTPUT_BROKEN

lib/Makefile

@@ -108,11 +108,7 @@ test_fpu-y := test_fpu_glue.o test_fpu_impl.o
 CFLAGS_test_fpu_impl.o += $(CC_FLAGS_FPU)
 CFLAGS_REMOVE_test_fpu_impl.o += $(CC_FLAGS_NO_FPU)
 
-# Some KUnit files (hooks.o) need to be built-in even when KUnit is a module,
-# so we can't just use obj-$(CONFIG_KUNIT).
-ifdef CONFIG_KUNIT
 obj-y += kunit/
-endif
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG

lib/kunit/Kconfig

@@ -93,4 +93,14 @@ config KUNIT_AUTORUN_ENABLED
 	  In most cases this should be left as Y. Only if additional opt-in
 	  behavior is needed should this be set to N.
 
+config KUNIT_UAPI
+	def_bool y
+	depends on KUNIT=y
+	depends on CC_CAN_LINK_STATIC || ARCH_HAS_NOLIBC
+	select HEADERS_INSTALL
+	help
+	  Enables support for building and running userspace selftests as part of kunit.
+	  These tests should be statically linked and use kselftest.h or kselftest_harness.h
+	  for status reporting.
+
 endif # KUNIT

lib/kunit/Makefile

@@ -12,12 +12,21 @@ kunit-objs +=				test.o \
 					device.o \
 					platform.o
 
+userprogs +=				uapi-preinit
+uapi-preinit-nolibc :=			$(CONFIG_ARCH_HAS_NOLIBC)
+uapi-preinit-userccflags +=		-static \
+					-include include/generated/autoconf.h \
+					-include $(srctree)/tools/include/linux/kconfig.h
+blobs +=				uapi-preinit.blob.o
+uapi-preinit.blob-symbol :=		kunit_uapi_preinit
+kunit-$(CONFIG_KUNIT_UAPI) +=		uapi.o uapi-preinit.blob.o
+
 ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
 kunit-objs +=				debugfs.o
 endif
 
 # KUnit 'hooks' are built-in even when KUnit is built as a module.
-obj-y +=				hooks.o
+obj-$(if $(CONFIG_KUNIT),y) +=		hooks.o
 
 obj-$(CONFIG_KUNIT_TEST) +=		kunit-test.o
 obj-$(CONFIG_KUNIT_TEST) +=		platform-test.o
@@ -28,4 +37,11 @@ obj-$(CONFIG_KUNIT_TEST) +=		string-stream-test.o
 obj-$(CONFIG_KUNIT_TEST) +=		assert_test.o
 endif
 
-obj-$(CONFIG_KUNIT_EXAMPLE_TEST) +=	kunit-example-test.o
+userprogs +=				kunit-example-uapi
+kunit-example-uapi-userccflags :=	-static
+kunit-example-uapi-nolibc :=		$(CONFIG_ARCH_HAS_NOLIBC)
+blobs +=				kunit-example-uapi.blob.o
+
+obj-$(CONFIG_KUNIT_EXAMPLE_TEST) +=	kunit-example-mod.o
+kunit-example-mod-y +=			kunit-example-test.o
+kunit-example-mod-$(CONFIG_KUNIT_UAPI) += kunit-example-uapi.blob.o

lib/kunit/kunit-example-test.c

@@ -6,8 +6,11 @@
  * Author: Brendan Higgins <brendanhiggins@google.com>
  */
 
+#include <linux/blob.h>
+
 #include <kunit/test.h>
 #include <kunit/static_stub.h>
+#include <kunit/uapi.h>
 
 /*
  * This is the most fundamental element of KUnit, the test case. A test case
@@ -277,6 +280,17 @@ static void example_slow_test(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, 1 + 1, 2);
 }
 
+/*
+ * This test shows the usage of UAPI tests.
+ */
+static void example_uapi_test(struct kunit *test)
+{
+	if (IS_ENABLED(CONFIG_KUNIT_UAPI))
+		kunit_uapi_run_kselftest(test, BLOB(kunit_example_uapi));
+	else
+		kunit_skip(test, "CONFIG_KUNIT_UAPI is not enabled");
+}
+
 /*
  * Here we make a list of all the test cases we want to add to the test suite
  * below.
@@ -297,6 +311,7 @@ static struct kunit_case example_test_cases[] = {
 	KUNIT_CASE(example_priv_test),
 	KUNIT_CASE_PARAM(example_params_test, example_gen_params),
 	KUNIT_CASE_SLOW(example_slow_test),
+	KUNIT_CASE(example_uapi_test),
 	{}
 };
 

lib/kunit/kunit-example-uapi.c

@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit Userspace example test.
+ *
+ * Copyright (C) 2025, Linutronix GmbH.
+ * Author: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
+ *
+ * This is *userspace* code.
+ */
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+
+#include "../../tools/testing/selftests/kselftest.h"
+
+static void test_procfs(void)
+{
+	char buf[256];
+	ssize_t r;
+	int fd;
+
+	fd = open("/proc/self/comm", O_RDONLY);
+	if (fd == -1) {
+		ksft_test_result_fail("procfs: open() failed: %s\n", strerror(errno));
+		return;
+	}
+
+	r = read(fd, buf, sizeof(buf));
+	close(fd);
+
+	if (r == -1) {
+		ksft_test_result_fail("procfs: read() failed: %s\n", strerror(errno));
+		return;
+	}
+
+	if (r != 16 || strncmp("kunit-example-u\n", buf, 16) != 0) {
+		ksft_test_result_fail("procfs: incorrect comm\n");
+		return;
+	}
+
+	ksft_test_result_pass("procfs\n");
+}
+
+int main(void)
+{
+	ksft_print_header();
+	ksft_set_plan(4);
+	test_procfs();
+	ksft_test_result_pass("userspace test 2\n");
+	ksft_test_result_skip("userspace test 3: some reason\n");
+	ksft_test_result_pass("userspace test 4\n");
+	ksft_finished();
+}