Date:   Tue, 24 Jan 2023 16:03:50 +0800
Mime-Version: 1.0
Message-ID: <20230124080350.2275652-1-davidgow@google.com>
Subject: [RFC PATCH v2] kunit: Add "hooks" to call into KUnit when it's built
 as a module
From:   David Gow <davidgow@google.com>
To:     Brendan Higgins <brendan.higgins@linux.dev>,
        Kees Cook <keescook@chromium.org>,
        Shuah Khan <skhan@linuxfoundation.org>,
        Daniel Latypov <dlatypov@google.com>,
        Rae Moar <rmoar@google.com>
Cc:     Sadiya Kazi <sadiyakazi@google.com>, kunit-dev@googlegroups.com,
        linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
        David Gow <davidgow@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

KUnit has several macros and functions intended for use from non-test
code. These hooks, currently the kunit_get_current_test() and
kunit_fail_current_test() macros, didn't work when CONFIG_KUNIT=m.

In order to support this case, the required functions and static data
need to be available unconditionally, even when KUnit itself is not
built-in. The new 'hooks.c' file is therefore always included, and has
both the static key required for kunit_get_current_test(), and a
function pointer to the real implementation of
__kunit_fail_current_test(), which is populated when the KUnit module is
loaded.

A new header, kunit/hooks-table.h, contains a table of all hooks, and is
repeatedly included with different definitions of the KUNIT_HOOK() in
order to automatically generate the needed function pointer tables. When
KUnit is disabled, or the module is not loaded, these function pointers
are all NULL. This shouldn't be a problem, as they're all used behind
wrappers which check kunit_running and/or that the pointer is non-NULL.

This can then be extended for future features which require similar
"hook" behaviour, such as static stubs:
https://lore.kernel.org/all/20221208061841.2186447-1-davidgow@google.com/

Signed-off-by: David Gow <davidgow@google.com>
---

This is basically a prerequisite for the stub features working when
KUnit is built as a module, and should nicely make a few other tests
work then, too.

v2 adds a slightly-excessive macro-based system for defining hooks. This
made adding the static stub hooks absolutely trivial, and the complexity
is totally hidden from the user (being an internal KUnit implementation
detail), so I'm more comfortable with this than some other macro magic.

It does however result in a huge number of checkpatch.pl errors, as
we're using macros in unconventional ways, and checkpatch just can't
work out the syntax. These are mostly "Macros with complex values should
be enclosed in parentheses", "Macros with multiple statements should be
enclosed in a do - while loop", and similar, which don't apply due to
the macros not being expressions: they are mostly declarations or
assignment statements. There are a few others where checkpatch thinks
that the return value is the function name and similar, so complains
about the style.

Open questions:
- Is this macro-based system worth it, or was v1 better?
- Should we rename test-bug.h to hooks.h or similar.
  (I think so, but would rather do it in a separate patch, to make it
  easier to review. There are a few includes of it scattered about.)
- Is making these NULL when KUnit isn't around sensible, or should we
  auto-generate a "default" implementation. This is a pretty easy
  extension to the macros here.
  (I think NULL is good for now, as we have wrappers for these anyway.
  If we want to change our minds later as we add more hooks, it's easy.)
- Any other thoughts?

Cheers,
-- David

Changes since RFC v1:
https://lore.kernel.org/all/20230117142737.246446-1-davidgow@google.com/
- Major refit to auto-generate the hook code using macros.
- (Note that previous Reviewed-by tags have not been added, as this is a
  big enough change it probably needs a re-reviews. Thanks Rae for
  reviewing RFC v1 previously, though!)
---
 Documentation/dev-tools/kunit/usage.rst | 14 +++++-----
 include/kunit/hooks-table.h             | 34 +++++++++++++++++++++++++
 include/kunit/test-bug.h                | 24 +++++++++--------
 lib/Makefile                            |  4 +++
 lib/kunit/Makefile                      |  3 +++
 lib/kunit/hooks.c                       | 27 ++++++++++++++++++++
 lib/kunit/test.c                        | 22 +++++++++++-----
 7 files changed, 103 insertions(+), 25 deletions(-)
 create mode 100644 include/kunit/hooks-table.h
 create mode 100644 lib/kunit/hooks.c

diff --git a/Documentation/dev-tools/kunit/usage.rst b/Documentation/dev-tools/kunit/usage.rst
index 48f8196d5aad..6424493b93cb 100644
--- a/Documentation/dev-tools/kunit/usage.rst
+++ b/Documentation/dev-tools/kunit/usage.rst
@@ -648,10 +648,9 @@ We can do this via the ``kunit_test`` field in ``task_struct``, which we can
 access using the ``kunit_get_current_test()`` function in ``kunit/test-bug.h``.
 
 ``kunit_get_current_test()`` is safe to call even if KUnit is not enabled. If
-KUnit is not enabled, was built as a module (``CONFIG_KUNIT=m``), or no test is
-running in the current task, it will return ``NULL``. This compiles down to
-either a no-op or a static key check, so will have a negligible performance
-impact when no test is running.
+KUnit is not enabled, or if no test is running in the current task, it will
+return ``NULL``. This compiles down to either a no-op or a static key check,
+so will have a negligible performance impact when no test is running.
 
 The example below uses this to implement a "mock" implementation of a function, ``foo``:
 
@@ -726,8 +725,7 @@ structures as shown below:
 	#endif
 
 ``kunit_fail_current_test()`` is safe to call even if KUnit is not enabled. If
-KUnit is not enabled, was built as a module (``CONFIG_KUNIT=m``), or no test is
-running in the current task, it will do nothing. This compiles down to either a
-no-op or a static key check, so will have a negligible performance impact when
-no test is running.
+KUnit is not enabled, or if no test is running in the current task, it will do
+nothing. This compiles down to either a no-op or a static key check, so will
+have a negligible performance impact when no test is running.
 
diff --git a/include/kunit/hooks-table.h b/include/kunit/hooks-table.h
new file mode 100644
index 000000000000..0b5eafd199ed
--- /dev/null
+++ b/include/kunit/hooks-table.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * KUnit 'Hooks' function pointer table
+ *
+ * This file is included multiple times, each time with a different definition
+ * of KUNIT_HOOK. This provides one place where all of the hooks can be listed
+ * which can then be converted into function / implementation declarations, or
+ * code to set function pointers.
+ *
+ * Copyright (C) 2023, Google LLC.
+ * Author: David Gow <davidgow@google.com>
+ */
+
+/*
+ * To declare a hook, use:
+ * KUNIT_HOOK(name, retval, args), where:
+ * - name: the function name of the exported hook
+ * - retval: the type of the return value of the hook
+ * - args: the arguments to the hook, of the form (int a, int b)
+ *
+ * Note that the argument list should be contained within the brackets (),
+ * and that the implementation of the hook should be in a <name>_impl
+ * function, which should not be declared static, but need not be exported.
+ */
+
+#ifndef KUNIT_HOOK
+#error KUNIT_HOOK must be defined before including the hooks table
+#endif
+
+KUNIT_HOOK(__kunit_fail_current_test, __printf(3, 4) void,
+	   (const char *file, int line, const char *fmt, ...));
+
+/* Undefine KUNIT_HOOK at the end, ready for the next use. */
+#undef KUNIT_HOOK
diff --git a/include/kunit/test-bug.h b/include/kunit/test-bug.h
index c1b2e14eab64..3203ffc0a08b 100644
--- a/include/kunit/test-bug.h
+++ b/include/kunit/test-bug.h
@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /*
- * KUnit API allowing dynamic analysis tools to interact with KUnit tests
+ * KUnit API providing hooks for non-test code to interact with tests.
  *
  * Copyright (C) 2020, Google LLC.
  * Author: Uriel Guajardo <urielguajardo@google.com>
@@ -9,7 +9,7 @@
 #ifndef _KUNIT_TEST_BUG_H
 #define _KUNIT_TEST_BUG_H
 
-#if IS_BUILTIN(CONFIG_KUNIT)
+#if IS_ENABLED(CONFIG_KUNIT)
 
 #include <linux/jump_label.h> /* For static branch */
 #include <linux/sched.h>
@@ -43,20 +43,21 @@ static inline struct kunit *kunit_get_current_test(void)
  * kunit_fail_current_test() - If a KUnit test is running, fail it.
  *
  * If a KUnit test is running in the current task, mark that test as failed.
- *
- * This macro will only work if KUnit is built-in (though the tests
- * themselves can be modules). Otherwise, it compiles down to nothing.
  */
 #define kunit_fail_current_test(fmt, ...) do {					\
 		if (static_branch_unlikely(&kunit_running)) {			\
+			/* Guaranteed to be non-NULL when kunit_running true*/	\
 			__kunit_fail_current_test(__FILE__, __LINE__,		\
 						  fmt, ##__VA_ARGS__);		\
 		}								\
 	} while (0)
 
 
-extern __printf(3, 4) void __kunit_fail_current_test(const char *file, int line,
-						    const char *fmt, ...);
+/* Declare all of the available hooks. */
+#define KUNIT_HOOK(name, retval, args) \
+	extern retval (*name)args
+
+#include "kunit/hooks-table.h"
 
 #else
 
@@ -66,10 +67,11 @@ static inline struct kunit *kunit_get_current_test(void) { return NULL; }
 #define kunit_fail_current_test(fmt, ...) \
 		__kunit_fail_current_test(__FILE__, __LINE__, fmt, ##__VA_ARGS__)
 
-static inline __printf(3, 4) void __kunit_fail_current_test(const char *file, int line,
-							    const char *fmt, ...)
-{
-}
+/* No-op stubs if KUnit is not enabled. */
+#define KUNIT_HOOK(name, retval, args) \
+	static retval (*name)args = NULL
+
+#include "kunit/hooks-table.h"
 
 #endif
 
diff --git a/lib/Makefile b/lib/Makefile
index 4d9461bfea42..9031de6ca73c 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -126,6 +126,10 @@ CFLAGS_test_fpu.o += $(FPU_CFLAGS)
 obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/
 
 obj-$(CONFIG_KUNIT) += kunit/
+# Include the KUnit hooks unconditionally. They'll compile to nothing if
+# CONFIG_KUNIT=n, otherwise will be a small table of static data (static key,
+# function pointers) which need to be built-in even when KUnit is a module.
+obj-y += kunit/hooks.o
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG
diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index 29aff6562b42..deeb46cc879b 100644
--- a/lib/kunit/Makefile
+++ b/lib/kunit/Makefile
@@ -11,6 +11,9 @@ ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
 kunit-objs +=				debugfs.o
 endif
 
+# KUnit 'hooks' are built-in even when KUnit is built as a module.
+lib-y +=				hooks.o
+
 obj-$(CONFIG_KUNIT_TEST) +=		kunit-test.o
 
 # string-stream-test compiles built-in only.
diff --git a/lib/kunit/hooks.c b/lib/kunit/hooks.c
new file mode 100644
index 000000000000..29e81614f486
--- /dev/null
+++ b/lib/kunit/hooks.c
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit 'Hooks' implementation.
+ *
+ * This file contains code / structures which should be built-in even when
+ * KUnit itself is built as a module.
+ *
+ * Copyright (C) 2022, Google LLC.
+ * Author: David Gow <davidgow@google.com>
+ */
+
+/* This file is always built-in, so make sure it's empty if CONFIG_KUNIT=n */
+#if IS_ENABLED(CONFIG_KUNIT)
+
+#include <kunit/test-bug.h>
+
+DEFINE_STATIC_KEY_FALSE(kunit_running);
+EXPORT_SYMBOL(kunit_running);
+
+/* Function pointers for hooks. */
+#define KUNIT_HOOK(name, retval, args) \
+	retval (*name)args; \
+	EXPORT_SYMBOL(name)
+
+#include "kunit/hooks-table.h"
+
+#endif
diff --git a/lib/kunit/test.c b/lib/kunit/test.c
index c9ebf975e56b..b6c88f722b68 100644
--- a/lib/kunit/test.c
+++ b/lib/kunit/test.c
@@ -20,13 +20,10 @@
 #include "string-stream.h"
 #include "try-catch-impl.h"
 
-DEFINE_STATIC_KEY_FALSE(kunit_running);
-
-#if IS_BUILTIN(CONFIG_KUNIT)
 /*
  * Fail the current test and print an error message to the log.
  */
-void __kunit_fail_current_test(const char *file, int line, const char *fmt, ...)
+void __kunit_fail_current_test_impl(const char *file, int line, const char *fmt, ...)
 {
 	va_list args;
 	int len;
@@ -53,8 +50,6 @@ void __kunit_fail_current_test(const char *file, int line, const char *fmt, ...)
 	kunit_err(current->kunit_test, "%s:%d: %s", file, line, buffer);
 	kunit_kfree(current->kunit_test, buffer);
 }
-EXPORT_SYMBOL_GPL(__kunit_fail_current_test);
-#endif
 
 /*
  * Enable KUnit tests to run.
@@ -775,8 +770,18 @@ void kunit_cleanup(struct kunit *test)
 }
 EXPORT_SYMBOL_GPL(kunit_cleanup);
 
+/* Declarations for the hook implemetnations */
+#define KUNIT_HOOK(name, retval, args) \
+	extern retval name##_impl args
+#include "kunit/hooks-table.h"
+
 static int __init kunit_init(void)
 {
+	/* Install the KUnit hook functions. */
+#define KUNIT_HOOK(name, retval, args) \
+	name = name##_impl
+#include "kunit/hooks-table.h"
+
 	kunit_debugfs_init();
 #ifdef CONFIG_MODULES
 	return register_module_notifier(&kunit_mod_nb);
@@ -788,6 +793,11 @@ late_initcall(kunit_init);
 
 static void __exit kunit_exit(void)
 {
+	/* Remove the KUnit hook functions. */
+#define KUNIT_HOOK(name, retval, args) \
+	name = NULL
+#include "kunit/hooks-table.h"
+
 #ifdef CONFIG_MODULES
 	unregister_module_notifier(&kunit_mod_nb);
 #endif
-- 
2.39.0.246.g2a6d74b583-goog