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

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Message-ID: <202503071227.578545FF9@keescook>
Date: Fri, 7 Mar 2025 12:30:36 -0800
From: Kees Cook <kees@...nel.org>
To: Jan Kara <jack@...e.cz>
Cc: sunliming@...ux.dev, 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 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;

> 
> 								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

-- 
Kees Cook