include/kunit/static_stub.h

   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