linux-kernel - Re: [PATCH v2 5/6] kunit: split out part of kunit

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Date:   Tue, 11 Jan 2022 16:42:29 -0500
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Daniel Latypov <dlatypov@...gle.com>
Cc:     davidgow@...gle.com, linux-kernel@...r.kernel.org,
        kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
        skhan@...uxfoundation.org, torvalds@...ux-foundation.org
Subject: Re: [PATCH v2 5/6] kunit: split out part of kunit_assert into a
 static const

On Tue, Jan 11, 2022 at 4:35 PM Brendan Higgins
<brendanhiggins@...gle.com> wrote:
>
> On Tue, Jan 11, 2022 at 2:42 PM Daniel Latypov <dlatypov@...gle.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@...gle.com>
> > Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> > Reviewed-by: David Gow <davidgow@...gle.com>
>
> One question below, but other than that,
>
> Reviewed-by: Brendan Higgins <brendanhiggins@...gle.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@...gle.com): delete this
>
> Can you provide some context for this?

NVM, I saw the context in the next patch. Could you maybe mention that
it is removed in a later patch in the comment?

> >         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