linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: Eliminate usage of uninitialized

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Message-ID: <f40aa2cc-5675-b8a2-b14f-10edf63d748a@huawei.com>
Date:   Mon, 15 Jun 2020 16:38:37 +0800
From:   Jason Yan <yanaijie@...wei.com>
To:     Chao Yu <yuchao0@...wei.com>, <jaegeuk@...nel.org>,
        <chao@...nel.org>, <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
CC:     Kees Cook <keescook@...omium.org>,
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: Eliminate usage of uninitialized_var()
 macro


在 2020/6/15 16:26, Chao Yu 写道:
> On 2020/6/15 12:02, Jason Yan wrote:
>> This is an effort to eliminate the uninitialized_var() macro[1].
>>
>> The use of this macro is the wrong solution because it forces off ANY
>> analysis by the compiler for a given variable. It even masks "unused
>> variable" warnings.
>>
>> Quoted from Linus[2]:
>>
>> "It's a horrible thing to use, in that it adds extra cruft to the
>> source code, and then shuts up a compiler warning (even the _reliable_
>> warnings from gcc)."
>>
>> The gcc option "-Wmaybe-uninitialized" has been disabled and this change
>> will not produce any warnnings even with "make W=1".
>>
>> [1] https://github.com/KSPP/linux/issues/81
>> [2] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
>>
>> Cc: Kees Cook <keescook@...omium.org>
>> Signed-off-by: Jason Yan <yanaijie@...wei.com>
>> ---
>>   fs/f2fs/data.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>> index 326c63879ddc..e6ec61274d76 100644
>> --- a/fs/f2fs/data.c
>> +++ b/fs/f2fs/data.c
>> @@ -2856,7 +2856,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
>>   	};
>>   #endif
>>   	int nr_pages;
>> -	pgoff_t uninitialized_var(writeback_index);
>> +	pgoff_t writeback_index;
> 
> I suggest to delete this variable directly, as we did for mm in
> commit 28659cc8cc87 (mm/page-writeback.c: remove unused variable).
> 

Good suggestion, I will send v2.

Thanks,
Jason

> Thanks,
> 
>>   	pgoff_t index;
>>   	pgoff_t end;		/* Inclusive */
>>   	pgoff_t done_index;
>>
> 
> .
>