linux-kernel - Re: [PATCH] btrfs: fix Wmaybe-uninitialized warning

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Date:   Tue, 17 Sep 2019 12:12:23 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Austin Kim <austindh.kim@...il.com>
Cc:     clm@...com, josef@...icpanda.com, dsterba@...e.com,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: fix Wmaybe-uninitialized warning

On Tue, Sep 03, 2019 at 12:30:19PM +0900, Austin Kim wrote:
> gcc throws warning message as below:

What version of gcc reports that? 9.2.1 does not.

> ‘clone_src_i_size’ may be used uninitialized in this function
> [-Wmaybe-uninitialized]
>  #define IS_ALIGNED(x, a)  (((x) & ((typeof(x))(a) - 1)) == 0)
>                        ^
> fs/btrfs/send.c:5088:6: note: ‘clone_src_i_size’ was declared here
>  u64 clone_src_i_size;
>    ^
> The clone_src_i_size is only used as call-by-reference
> in a call to get_inode_info().

The reference is passed to a static function, so the compiler has enough
information to determine if it's unused. By inspection I don't see a
problem with the uninitalized variable: if __get_inode_info succeeds,
there's a valid value, in error case it's not used at all.