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From:   Brendan Higgins <brendanhiggins@google.com>
Date:   Tue, 11 Jan 2022 16:35:23 -0500
Message-ID: <CAFd5g46bCr4DEqruLbtgcLOpuPQUgS32ePDicrezBwOXL_r5Hg@mail.gmail.com>
Subject: Re: [PATCH v2 5/6] kunit: split out part of kunit_assert into a
 static const
To:     Daniel Latypov <dlatypov@google.com>
Cc:     davidgow@google.com, linux-kernel@vger.kernel.org,
        kunit-dev@googlegroups.com, linux-kselftest@vger.kernel.org,
        skhan@linuxfoundation.org, torvalds@linux-foundation.org
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On Tue, Jan 11, 2022 at 2:42 PM Daniel Latypov <dlatypov@google.com> wrote:
>
> This is per Linus's suggestion in [1].
>
> The issue there is that every KUNIT_EXPECT/KUNIT_ASSERT puts a
> kunit_assert object onto the stack. Normally we rely on compilers to
> elide this, but when that doesn't work out, this blows up the stack
> usage of kunit test functions.
>
> We can move some data off the stack by making it static.
> This change introduces a new `struct kunit_loc` to hold the file and
> line number and then just passing assert_type (EXPECT or ASSERT) as an
> argument.
>
> In [1], it was suggested to also move out the format string as well, but
> users could theoretically craft a format string at runtime, so we can't.
>
> This change leaves a copy of `assert_type` in kunit_assert for now
> because cleaning up all the macros to not pass it around is a bit more
> involved.
>
> Here's an example of the expanded code for KUNIT_FAIL():
> if (__builtin_expect(!!(!(false)), 0)) {
>   static const struct kunit_loc loc = { .file = ... };
>   struct kunit_fail_assert __assertion = { .assert = { .type ...  };
>   kunit_do_failed_assertion(test, &loc, KUNIT_EXPECTATION, &__assertion.assert, ...);
> };
>
> [1] https://groups.google.com/g/kunit-dev/c/i3fZXgvBrfA/m/VULQg1z6BAAJ
>
> Signed-off-by: Daniel Latypov <dlatypov@google.com>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Reviewed-by: David Gow <davidgow@google.com>

One question below, but other than that,

Reviewed-by: Brendan Higgins <brendanhiggins@google.com>

> ---
>  include/kunit/assert.h | 25 ++++++++++++++++---------
>  include/kunit/test.h   | 12 +++++++++++-
>  lib/kunit/assert.c     |  9 +++++----
>  lib/kunit/test.c       | 15 +++++++++------
>  4 files changed, 41 insertions(+), 20 deletions(-)
>
> diff --git a/include/kunit/assert.h b/include/kunit/assert.h
> index 3da6c792496c..4f91dbdb886a 100644
> --- a/include/kunit/assert.h
> +++ b/include/kunit/assert.h
> @@ -28,11 +28,21 @@ enum kunit_assert_type {
>         KUNIT_EXPECTATION,
>  };
>
> +/**
> + * struct kunit_loc - Identifies the source location of a line of code.
> + * @line: the line number in the file.
> + * @file: the file name.
> + */
> +struct kunit_loc {
> +       int line;
> +       const char *file;
> +};
> +
> +#define KUNIT_CURRENT_LOC { .file = __FILE__, .line = __LINE__ }
> +
>  /**
>   * struct kunit_assert - Data for printing a failed assertion or expectation.
>   * @type: the type (either an expectation or an assertion) of this kunit_assert.
> - * @line: the source code line number that the expectation/assertion is at.
> - * @file: the file path of the source file that the expectation/assertion is in.
>   * @message: an optional message to provide additional context.
>   * @format: a function which formats the data in this kunit_assert to a string.
>   *
> @@ -40,9 +50,7 @@ enum kunit_assert_type {
>   * format a string to a user reporting the failure.
>   */
>  struct kunit_assert {
> -       enum kunit_assert_type type;
> -       int line;
> -       const char *file;
> +       enum kunit_assert_type type; // TODO(dlatypov@google.com): delete this

Can you provide some context for this?

>         struct va_format message;
>         void (*format)(const struct kunit_assert *assert,
>                        struct string_stream *stream);
> @@ -65,14 +73,13 @@ struct kunit_assert {
>   */
>  #define KUNIT_INIT_ASSERT_STRUCT(assert_type, fmt) {                          \
>         .type = assert_type,                                                   \
> -       .file = __FILE__,                                                      \
> -       .line = __LINE__,                                                      \
>         .message = KUNIT_INIT_VA_FMT_NULL,                                     \
>         .format = fmt                                                          \
>  }
>
> -void kunit_base_assert_format(const struct kunit_assert *assert,
> -                             struct string_stream *stream);
> +void kunit_assert_prologue(const struct kunit_loc *loc,
> +                          enum kunit_assert_type type,
> +                          struct string_stream *stream);
>
>  void kunit_assert_print_msg(const struct kunit_assert *assert,
>                             struct string_stream *stream);
> diff --git a/include/kunit/test.h b/include/kunit/test.h
> index 25ea3bce6663..7b752175e614 100644
> --- a/include/kunit/test.h
> +++ b/include/kunit/test.h