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Date:   Mon, 7 Dec 2020 09:15:56 +0100
From:   Michal Kubecek <mkubecek@suse.cz>
To:     Alex Shi <alex.shi@linux.alibaba.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Souptick Joarder <jrdr.linux@gmail.com>,
        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>
Subject: Re: [PATCH] mm/filemap: add static for function
 __add_to_page_cache_locked
Message-ID: <20201207081556.pwxmhgdxayzbofpi@lion.mk-sys.cz>
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On Thu, Nov 12, 2020 at 08:18:57AM +0800, Alex Shi wrote:
> 
> 
> 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? 

It's probably more complicated: our v5.10-rc7 builds with
CONFIG_DEBUG_INFO_BTF=y fail on ppc64 and ppc64le with

     BTFIDS  vmlinux
   FAILED unresolved symbol __add_to_page_cache_locked


but succeed on x86_64, i586, aarch64 and s390x. So far I don't see why
this should depend on architecture.

Michal