linux-kernel - Re: [PATCH] fs: binfmt_elf_efpic: fix variable set but not used warning

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Message-ID: <fe4802f2-f81b-6e33-6ee1-af2f3771f8fc@linux.dev>
Date: Sat, 8 Mar 2025 10:21:37 +0800
From: Sunliming <sunliming@...ux.dev>
To: Kees Cook <kees@...nel.org>, Jan Kara <jack@...e.cz>
Cc: viro@...iv.linux.org.uk, brauner@...nel.org, ebiederm@...ssion.com,
 linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, sunliming@...inos.cn,
 kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] fs: binfmt_elf_efpic: fix variable set but not used
 warning


On 2025/3/8 04:30, Kees Cook wrote:
> On Fri, Mar 07, 2025 at 03:47:28PM +0100, Jan Kara wrote:
>> On Fri 07-03-25 14:11:28, sunliming@...ux.dev wrote:
>>> From: sunliming <sunliming@...inos.cn>
>>>
>>> Fix below kernel warning:
>>> fs/binfmt_elf_fdpic.c:1024:52: warning: variable 'excess1' set but not
>>> used [-Wunused-but-set-variable]
>>>
>>> Reported-by: kernel test robot <lkp@...el.com>
>>> Signed-off-by: sunliming <sunliming@...inos.cn>
>> The extra ifdef is not pretty but I guess it's better. Feel free to add:
>>
>> Reviewed-by: Jan Kara <jack@...e.cz>
> Since we allow loop-scope variable definitions now, perhaps this is a
> case for defining the variable later within the #ifdef, like this?
>
>
> diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
> index e3cf2801cd64..b0ef71238328 100644
> --- a/fs/binfmt_elf_fdpic.c
> +++ b/fs/binfmt_elf_fdpic.c
> @@ -1024,7 +1024,7 @@ static int elf_fdpic_map_file_by_direct_mmap(struct elf_fdpic_params *params,
>   	/* deal with each load segment separately */
>   	phdr = params->phdrs;
>   	for (loop = 0; loop < params->hdr.e_phnum; loop++, phdr++) {
> -		unsigned long maddr, disp, excess, excess1;
> +		unsigned long maddr, disp, excess;
>   		int prot = 0, flags;
>   
>   		if (phdr->p_type != PT_LOAD)
> @@ -1120,9 +1120,10 @@ static int elf_fdpic_map_file_by_direct_mmap(struct elf_fdpic_params *params,
>   		 *   extant in the file
>   		 */
>   		excess = phdr->p_memsz - phdr->p_filesz;
> -		excess1 = PAGE_SIZE - ((maddr + phdr->p_filesz) & ~PAGE_MASK);
>   
>   #ifdef CONFIG_MMU
> +		const unsigned long excess1 =
> +			PAGE_SIZE - ((maddr + phdr->p_filesz) & ~PAGE_MASK);
>   		if (excess > excess1) {
>   			unsigned long xaddr = maddr + phdr->p_filesz + excess1;
>   			unsigned long xmaddr;
I think this is a good idea. I will resend this patch in this way，thanks.
>> 								Honza
>>
>>> ---
>>>   fs/binfmt_elf_fdpic.c | 7 +++++--
>>>   1 file changed, 5 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
>>> index e3cf2801cd64..bed13ee8bfec 100644
>>> --- a/fs/binfmt_elf_fdpic.c
>>> +++ b/fs/binfmt_elf_fdpic.c
>>> @@ -1024,8 +1024,11 @@ static int elf_fdpic_map_file_by_direct_mmap(struct elf_fdpic_params *params,
>>>   	/* deal with each load segment separately */
>>>   	phdr = params->phdrs;
>>>   	for (loop = 0; loop < params->hdr.e_phnum; loop++, phdr++) {
>>> -		unsigned long maddr, disp, excess, excess1;
>>> +		unsigned long maddr, disp, excess;
>>>   		int prot = 0, flags;
>>> +#ifdef CONFIG_MMU
>>> +		unsigned long excess1;
>>> +#endif
>>>   
>>>   		if (phdr->p_type != PT_LOAD)
>>>   			continue;
>>> @@ -1120,9 +1123,9 @@ static int elf_fdpic_map_file_by_direct_mmap(struct elf_fdpic_params *params,
>>>   		 *   extant in the file
>>>   		 */
>>>   		excess = phdr->p_memsz - phdr->p_filesz;
>>> -		excess1 = PAGE_SIZE - ((maddr + phdr->p_filesz) & ~PAGE_MASK);
>>>   
>>>   #ifdef CONFIG_MMU
>>> +		excess1 = PAGE_SIZE - ((maddr + phdr->p_filesz) & ~PAGE_MASK);
>>>   		if (excess > excess1) {
>>>   			unsigned long xaddr = maddr + phdr->p_filesz + excess1;
>>>   			unsigned long xmaddr;
>>> -- 
>>> 2.25.1
>>>
>> -- 
>> Jan Kara <jack@...e.com>
>> SUSE Labs, CR