1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3  * KUnit function redirection (static stubbing) API.
4  *
5  * Copyright (C) 2022, Google LLC.
6  * Author: David Gow <davidgow@google.com>
7  */
8 #ifndef _KUNIT_STATIC_STUB_H
9 #define _KUNIT_STATIC_STUB_H
10 
11 #if !IS_ENABLED(CONFIG_KUNIT)
12 
13 /* If CONFIG_KUNIT is not enabled, these stubs quietly disappear. */
14 #define KUNIT_STATIC_STUB_REDIRECT(real_fn_name, args...) do {} while (0)
15 
16 #else
17 
18 #include <kunit/test.h>
19 #include <kunit/test-bug.h>
20 
21 #include <linux/compiler.h> /* for {un,}likely() */
22 #include <linux/sched.h> /* for task_struct */
23 
24 
25 /**
26  * KUNIT_STATIC_STUB_REDIRECT() - call a replacement 'static stub' if one exists
27  * @real_fn_name: The name of this function (as an identifier, not a string)
28  * @args: All of the arguments passed to this function
29  *
30  * This is a function prologue which is used to allow calls to the current
31  * function to be redirected by a KUnit test. KUnit tests can call
32  * kunit_activate_static_stub() to pass a replacement function in. The
33  * replacement function will be called by KUNIT_STATIC_STUB_REDIRECT(), which
34  * will then return from the function. If the caller is not in a KUnit context,
35  * the function will continue execution as normal.
36  *
37  * Example:
38  *
39  * .. code-block:: c
40  *
41  *	int real_func(int n)
42  *	{
43  *		KUNIT_STATIC_STUB_REDIRECT(real_func, n);
44  *		return 0;
45  *	}
46  *
47  *	int replacement_func(int n)
48  *	{
49  *		return 42;
50  *	}
51  *
52  *	void example_test(struct kunit *test)
53  *	{
54  *		kunit_activate_static_stub(test, real_func, replacement_func);
55  *		KUNIT_EXPECT_EQ(test, real_func(1), 42);
56  *	}
57  *
58  */
59 #define KUNIT_STATIC_STUB_REDIRECT(real_fn_name, args...)		\
60 do {									\
61 	typeof(&real_fn_name) replacement;				\
62 	struct kunit *current_test = kunit_get_current_test();		\
63 									\
64 	if (likely(!current_test))					\
65 		break;							\
66 									\
67 	replacement = kunit_hooks.get_static_stub_address(current_test,	\
68 							&real_fn_name);	\
69 									\
70 	if (unlikely(replacement))					\
71 		return replacement(args);				\
72 } while (0)
73 
74 /* Helper function for kunit_activate_static_stub(). The macro does
75  * typechecking, so use it instead.
76  */
77 void __kunit_activate_static_stub(struct kunit *test,
78 				  void *real_fn_addr,
79 				  void *replacement_addr);
80 
81 /**
82  * kunit_activate_static_stub() - replace a function using static stubs.
83  * @test: A pointer to the 'struct kunit' test context for the current test.
84  * @real_fn_addr: The address of the function to replace.
85  * @replacement_addr: The address of the function to replace it with.
86  *
87  * When activated, calls to real_fn_addr from within this test (even if called
88  * indirectly) will instead call replacement_addr. The function pointed to by
89  * real_fn_addr must begin with the static stub prologue in
90  * KUNIT_STATIC_STUB_REDIRECT() for this to work. real_fn_addr and
91  * replacement_addr must have the same type.
92  *
93  * The redirection can be disabled again with kunit_deactivate_static_stub().
94  */
95 #define kunit_activate_static_stub(test, real_fn_addr, replacement_addr) do {	\
96 	typecheck_fn(typeof(&replacement_addr), real_fn_addr);			\
97 	__kunit_activate_static_stub(test, real_fn_addr, replacement_addr);	\
98 } while (0)
99 
100 
101 /**
102  * kunit_deactivate_static_stub() - disable a function redirection
103  * @test: A pointer to the 'struct kunit' test context for the current test.
104  * @real_fn_addr: The address of the function to no-longer redirect
105  *
106  * Deactivates a redirection configured with kunit_activate_static_stub(). After
107  * this function returns, calls to real_fn_addr() will execute the original
108  * real_fn, not any previously-configured replacement.
109  */
110 void kunit_deactivate_static_stub(struct kunit *test, void *real_fn_addr);
111 
112 #endif
113 #endif
114