linux-kernel - Re: [PATCH] kcov: add missing #include <linux/sched.h>

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Message-ID: <20161206110905.GA24177@leverpostej>
Date:   Tue, 6 Dec 2016 11:09:05 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     linux-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        James Morse <james.morse@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] kcov: add missing #include <linux/sched.h>

On Tue, Dec 06, 2016 at 02:56:24PM +0800, Kefeng Wang wrote:
> It is needed by struct task_struct, fixes the following build problem
> with old gcc:
> 
> ../kernel/kcov.c: In function ‘__sanitizer_cov_trace_pc’:
> ../kernel/kcov.c:66: error: dereferencing pointer to incomplete type
> 	......
> ../kernel/kcov.c:239: error: dereferencing pointer to incomplete type
> 

It's somewhat confusing to strip the useful part of the error message
(which mentions task struct).

How about:

  In __sanitizer_cov_trace_pc we use task_struct and fields within it,
  but as we haven't included <linux/sched.h>, it is not guaranteed to be
  defined. While we usually happen to acquire the definition through a
  transitive include, this is fragile (and hasn't been true in the past,
  causing issues with backports).

  Include <linux/sched.h> to avoid any fragility.

Either way this looks like a sensible fix/cleanup, so FWIW:

Acked-by: Mark Rutland <mark.rutland@....com>

It looks like we're missing some other headers (e.g. <linux/export.h>
for EXPORT_SYMBOL(), <linux/preempt.h> for preempt_count() and friends).
It may be worth fixing all of those at once.

Thanks,
Mark.

> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> ---
> 
> note:
> - Build error occurred when I backported kcov to an old kernel version
>   with an old gcc
> 
>  kernel/kcov.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 30e6d05..3cbb0c8 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -7,6 +7,7 @@
>  #include <linux/fs.h>
>  #include <linux/mm.h>
>  #include <linux/printk.h>
> +#include <linux/sched.h>
>  #include <linux/slab.h>
>  #include <linux/spinlock.h>
>  #include <linux/vmalloc.h>
> -- 
> 1.7.12.4
>