linux-kernel - Re: [RFC PATCH 1/2] kunit: Expose 'static stub' API to redirect functions

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Date:   Wed, 4 May 2022 16:42:30 -0400
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Daniel Latypov <dlatypov@...gle.com>
Cc:     David Gow <davidgow@...gle.com>, Kees Cook <keescook@...omium.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] kunit: Expose 'static stub' API to redirect functions

On Wed, May 4, 2022 at 4:35 PM Daniel Latypov <dlatypov@...gle.com> wrote:
>
> On Thu, Mar 17, 2022 at 9:13 PM David Gow <davidgow@...gle.com> wrote:
> > +#define kunit_activate_static_stub(test, real_fn_addr, replacement_addr) do {  \
> > +       typecheck(typeof(real_fn_addr), replacement_addr);                      \
>
> We can't call this macro in the same scope for functions w/ different
> signatures.
>
> E.g. if we add this func to the example test
>   static void other_func(void) {}
> then trying to call kunit_activate_static_stub() on it in the same
> test case, we get
>
> ./include/linux/typecheck.h:10:14: error: conflicting types for
> ‘__dummy’; have ‘void(void)’
>    10 | ({      type __dummy; \
>       |              ^~~~~~~
> ./include/kunit/static_stub.h:99:9: note: in expansion of macro ‘typecheck’
>    99 |         typecheck(typeof(real_fn_addr), replacement_addr);
>                  \
>       |         ^~~~~~~~~
> lib/kunit/example-test.c:64:9: note: in expansion of macro
> ‘kunit_activate_static_stub’
>    64 |         kunit_activate_static_stub(test, other_func, other_func);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~
> ./include/linux/typecheck.h:10:14: note: previous declaration of
> ‘__dummy’ with type ‘int(int)’
>    10 | ({      type __dummy; \
>       |              ^~~~~~~
> ./include/kunit/static_stub.h:99:9: note: in expansion of macro ‘typecheck’
>    99 |         typecheck(typeof(real_fn_addr), replacement_addr);
>                  \
>       |         ^~~~~~~~~
> lib/kunit/example-test.c:62:9: note: in expansion of macro
> ‘kunit_activate_static_stub’
>    62 |         kunit_activate_static_stub(test, add_one, subtract_one);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Afaict, the problem is that GCC thinks we're declaring a *function*
> called __dummy, not a variable.
> So it bleeds across the scope boundary of do-while unlike normal variables.

Yeah, I ran into that problem too. I posted a fix to gerrit. I have
been meaning to share it here.

> There's the typecheck_fn macro, but it doesn't work either.

That's weird. It worked for me.