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Subject: Re: [PATCH] mm/filemap: add static for function
 __add_to_page_cache_locked
To:     Andrew Morton <akpm@linux-foundation.org>,
        Souptick Joarder <jrdr.linux@gmail.com>
Cc:     Linux-MM <linux-mm@kvack.org>, linux-kernel@vger.kernel.org,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Josef Bacik <josef@toxicpanda.com>
References: <1604661895-5495-1-git-send-email-alex.shi@linux.alibaba.com>
 <CAFqt6zZU76NOF6uD_c1vRPmEHwOzLp9wEWAmSX2ficpQb0zf6g@mail.gmail.com>
 <20201110115037.f6a53faec8d65782ab65d8b4@linux-foundation.org>
From:   Alex Shi <alex.shi@linux.alibaba.com>
Message-ID: <ddca2a9e-ed89-5dec-b1af-4f2fd2c99b57@linux.alibaba.com>
Date:   Thu, 12 Nov 2020 08:18:57 +0800
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在 2020/11/11 上午3:50, Andrew Morton 写道:
> On Tue, 10 Nov 2020 08:39:24 +0530 Souptick Joarder <jrdr.linux@gmail.com> wrote:
> 
>> On Fri, Nov 6, 2020 at 4:55 PM Alex Shi <alex.shi@linux.alibaba.com> wrote:
>>>
>>> Otherwise it cause gcc warning:
>>>           ^~~~~~~~~~~~~~~
>>> ../mm/filemap.c:830:14: warning: no previous prototype for
>>> ‘__add_to_page_cache_locked’ [-Wmissing-prototypes]
>>>  noinline int __add_to_page_cache_locked(struct page *page,
>>>               ^~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> Is CONFIG_DEBUG_INFO_BTF enabled in your .config ?
> 
> hm, yes.

When the config enabled, compiling looks good untill pahole tool
used to get BTF info, but I still failed on a right version pahole
> 1.16. Sorry.

> 
>>>
>>> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>> Cc: linux-mm@kvack.org
>>> Cc: linux-kernel@vger.kernel.org
>>> ---
>>>  mm/filemap.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/mm/filemap.c b/mm/filemap.c
>>> index d90614f501da..249cf489f5df 100644
>>> --- a/mm/filemap.c
>>> +++ b/mm/filemap.c
>>> @@ -827,7 +827,7 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
>>>  }
>>>  EXPORT_SYMBOL_GPL(replace_page_cache_page);
>>>
>>> -noinline int __add_to_page_cache_locked(struct page *page,
>>> +static noinline int __add_to_page_cache_locked(struct page *page,
>>>                                         struct address_space *mapping,
>>>                                         pgoff_t offset, gfp_t gfp,
>>>                                         void **shadowp)
> 
> It's unclear to me whether BTF_ID() requires that the target symbol be
> non-static.  It doesn't actually reference the symbol:
> 
> #define BTF_ID(prefix, name) \
>         __BTF_ID(__ID(__BTF_ID__##prefix##__##name##__))
> 

The above usage make me thought BTF don't require the symbol, though
the symbol still exist in vmlinux with 'static'.

So any comments of this, Alexei? 

> Alexei, can you please comment?
>