From: Nick Desaulniers <ndesaulniers@google.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Nathan Chancellor <natechancellor@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Masahiro Yamada <masahiroy@kernel.org>,
Michal Marek <michal.lkml@markovi.net>,
Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@redhat.com>,
Jason Baron <jbaron@akamai.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
linux-arch <linux-arch@vger.kernel.org>,
Linux Memory Management List <linux-mm@kvack.org>,
clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH 3/6] tracing: Wrap section comparison in tracer_alloc_buffers with COMPARE_SECTIONS
Date: Wed, 19 Feb 2020 13:32:38 -0800 [thread overview]
Message-ID: <CAKwvOdktG0vZOZVtNJBk1COhOnLYv3MU5KNQ8Z40L4ph5QcnRg@mail.gmail.com> (raw)
In-Reply-To: <20200219195424.GW31668@ziepe.ca>
On Wed, Feb 19, 2020 at 11:54 AM Jason Gunthorpe <jgg@ziepe.ca> wrote:
>
> On Wed, Feb 19, 2020 at 11:11:19AM -0800, Nick Desaulniers wrote:
> > > Godbolt says clang is happy if it is written as:
> > >
> > > if (&__stop___trace_bprintk_fmt[0] != &__start___trace_bprintk_fmt[0])
> > >
> > > Which is probably the best compromise. The type here is const char
> > > *[], so it would be a shame to see it go.
> >
> > If the "address" is never dereferenced, but only used for arithmetic
> > (in a way that the the pointed to type is irrelevant), does the
> > pointed to type matter?
>
> The type is used here:
>
> if (*pos < start_index)
> return __start___trace_bprintk_fmt + *pos;
>
> The return expression should be a const char **
>
> Presumably the caller of find_next derferences it.
>
> Jason
And the callers of find_next just return the return value from
find_next, but suddenly as `void*` (find_next()'s return type is
`char**`). So it doesn't seem like the pointed to type matters, hence
the recommendation of `void` and then address-of (&) used in
comparison+arithmetic.
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2020-02-19 21:32 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-19 4:54 [PATCH 0/6] Silence some instances of -Wtautological-compare and enable globally Nathan Chancellor
2020-02-19 4:54 ` [PATCH 1/6] asm/sections: Add COMPARE_SECTIONS macro Nathan Chancellor
2020-02-19 4:54 ` [PATCH 2/6] kernel/extable: Wrap section comparison in sort_main_extable with COMPARE_SECTIONS Nathan Chancellor
2020-02-19 4:54 ` [PATCH 3/6] tracing: Wrap section comparison in tracer_alloc_buffers " Nathan Chancellor
2020-02-19 14:34 ` Steven Rostedt
2020-02-19 17:44 ` Nick Desaulniers
2020-02-19 18:16 ` Jason Gunthorpe
2020-02-19 19:09 ` Steven Rostedt
2020-02-19 19:11 ` Nick Desaulniers
2020-02-19 19:22 ` Nathan Chancellor
2020-02-19 19:43 ` Steven Rostedt
2020-02-19 19:54 ` Jason Gunthorpe
2020-02-19 21:32 ` Nick Desaulniers [this message]
2020-02-19 4:54 ` [PATCH 4/6] dynamic_debug: Wrap section comparison in dynamic_debug_init " Nathan Chancellor
2020-02-19 4:54 ` [PATCH 5/6] mm: kmemleak: Wrap section comparison in kmemleak_init " Nathan Chancellor
2020-02-19 4:54 ` [PATCH 6/6] kbuild: Enable -Wtautological-compare Nathan Chancellor
2020-04-21 4:03 ` [PATCH 0/6] Silence some instances of -Wtautological-compare and enable globally Andrew Morton
2020-04-21 4:32 ` Nathan Chancellor
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