[PATCH v1] driver core: Silence 'unused-but-set variable' warning

[PATCH v1] driver core: Silence 'unused-but-set variable' warning

[Ammar Faizi]

From: Ammar Faizi <ammarfaizi2@gnuweeb.org>

Compiling with clang-16:

  drivers/base/module.c:36:6: error: variable 'no_warn' set but not \
  used [-Werror,-Wunused-but-set-variable]
          int no_warn;
              ^
  1 error generated.

A reason the @no_warn variable exists is:
sysfs_create_link() return value needs not be ignored to silence
another warning.

So don't remove @no_warn, but add a '(void)no_warn;'.

Cc: LLVM Mailing List <llvm@lists.linux.dev>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---
 drivers/base/module.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/base/module.c b/drivers/base/module.c
index 46ad4d636731..42f0b3b9e7f8 100644
--- a/drivers/base/module.c
+++ b/drivers/base/module.c
@@ -59,22 +59,23 @@ void module_add_driver(struct module *mod, struct device_driver *drv)
 		return;
 
 	/* Don't check return codes; these calls are idempotent */
 	no_warn = sysfs_create_link(&drv->p->kobj, &mk->kobj, "module");
 	driver_name = make_driver_name(drv);
 	if (driver_name) {
 		module_create_drivers_dir(mk);
 		no_warn = sysfs_create_link(mk->drivers_dir, &drv->p->kobj,
 					    driver_name);
 		kfree(driver_name);
 	}
+	(void)no_warn;
 }
 
 void module_remove_driver(struct device_driver *drv)
 {
 	struct module_kobject *mk = NULL;
 	char *driver_name;
 
 	if (!drv)
 		return;
 
 	sysfs_remove_link(&drv->p->kobj, "module");

base-commit: 8395ae05cb5a2e31d36106e8c85efa11cda849be
-- 
Ammar Faizi

Re: [PATCH v1] driver core: Silence 'unused-but-set variable' warning

[Greg Kroah-Hartman]

On Fri, Dec 23, 2022 at 09:51:37PM +0700, Ammar Faizi wrote:
> From: Ammar Faizi <ammarfaizi2@gnuweeb.org>
> 
> Compiling with clang-16:
> 
>   drivers/base/module.c:36:6: error: variable 'no_warn' set but not \
>   used [-Werror,-Wunused-but-set-variable]
>           int no_warn;
>               ^
>   1 error generated.
> 
> A reason the @no_warn variable exists is:
> sysfs_create_link() return value needs not be ignored to silence
> another warning.
> 
> So don't remove @no_warn, but add a '(void)no_warn;'.
> 
> Cc: LLVM Mailing List <llvm@lists.linux.dev>
> Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
> ---
>  drivers/base/module.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/base/module.c b/drivers/base/module.c
> index 46ad4d636731..42f0b3b9e7f8 100644
> --- a/drivers/base/module.c
> +++ b/drivers/base/module.c
> @@ -59,22 +59,23 @@ void module_add_driver(struct module *mod, struct device_driver *drv)
>  		return;
>  
>  	/* Don't check return codes; these calls are idempotent */
>  	no_warn = sysfs_create_link(&drv->p->kobj, &mk->kobj, "module");
>  	driver_name = make_driver_name(drv);
>  	if (driver_name) {
>  		module_create_drivers_dir(mk);
>  		no_warn = sysfs_create_link(mk->drivers_dir, &drv->p->kobj,
>  					    driver_name);
>  		kfree(driver_name);
>  	}
> +	(void)no_warn;

Ick, no, that's horrid and is NOT ok for kernel code, sorry.

Please fix the compiler, this is not a "fix" in any sense of the word
and is not going to work at all for kernel code.

sorry,

greg k-h

Re: [PATCH v1] driver core: Silence 'unused-but-set variable' warning

[Ammar Faizi]

On 12/23/22 10:02 PM, Greg Kroah-Hartman wrote:
> Ick, no, that's horrid and is NOT ok for kernel code, sorry.
> 
> Please fix the compiler, this is not a "fix" in any sense of the word
> and is not going to work at all for kernel code.

Agree.

Sorry for the noise. It turned out I messed up my clang compiler flags.
I forgot to do a "git reset --hard" before recompiling.

This has nothing todo with the upstream kernel.

-- 
Ammar Faizi

Re: [PATCH v1] driver core: Silence 'unused-but-set variable' warning

[Nathan Chancellor]

On Fri, Dec 23, 2022 at 10:31:57PM +0700, Ammar Faizi wrote:
> On 12/23/22 10:02 PM, Greg Kroah-Hartman wrote:
> > Ick, no, that's horrid and is NOT ok for kernel code, sorry.
> > 
> > Please fix the compiler, this is not a "fix" in any sense of the word
> > and is not going to work at all for kernel code.

It is possible that the compiler should not emit
-Wunused-but-set-variable when the variable is assigned the return
value of a function marked with __attribute__((warn_unused_result)) but
neither compiler does that today, you'll see the exact same warning from
GCC 12.2.0:

  drivers/base/module.c: In function ‘module_add_driver’:
  drivers/base/module.c:36:13: error: variable ‘no_warn’ set but not used [-Werror=unused-but-set-variable]
     36 |         int no_warn;
        |             ^~~~~~~
  cc1: all warnings being treated as errors

This has come up before too:

https://lore.kernel.org/20210726201924.3202278-2-morbo@google.com/

> Agree.
> 
> Sorry for the noise. It turned out I messed up my clang compiler flags.
> I forgot to do a "git reset --hard" before recompiling.
> 
> This has nothing todo with the upstream kernel.

This warning is in W=1, which are warnings that we want to turn on at
some point but the current instances need to be fixed first, so I would
say this is still relevant to the upstream kernel.

Cheers,
Nathan