linux-kernel - Re: [PATCH] block: fix Werror=format with GCC 13

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Date:   Wed, 26 Oct 2022 09:18:13 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Martin Liška <mliska@...e.cz>,
        linux-kernel@...r.kernel.org
Cc:     linux-block@...r.kernel.org, axboe@...nel.dk
Subject: Re: [PATCH] block: fix Werror=format with GCC 13

On 24. 10. 22, 21:01, Martin Liška wrote:
> Starting with GCC 13, since
> [g3b3083a598ca3f4b] c: C2x enums wider than int [PR36113]
> 
> GCC promotes enum values with larger than integer types to a wider type.
> In case of the anonymous enum type in blk-iocost.c it is:
> 
> enum {
> 	MILLION			= 1000000,
> ...
> 
> 	WEIGHT_ONE		= 1 << 16,
> ...
> 	VTIME_PER_SEC_SHIFT	= 37,
> 	VTIME_PER_SEC		= 1LLU << VTIME_PER_SEC_SHIFT,
> ...
> 
> as seen VTIME_PER_SEC cannot fit into 32-bits (int type), thus one needs
> to use 'long unsigned int' in the format string.
> 
> It fixes then the following 2 warnings:
> 
> block/blk-iocost.c: In function ‘ioc_weight_prfill’:
> block/blk-iocost.c:3035:37: error: format ‘%u’ expects argument of type ‘unsigned int’, but argument 4 has type ‘long unsigned int’ [-Werror=format=]
>   3035 |                 seq_printf(sf, "%s %u\n", dname, iocg->cfg_weight / WEIGHT_ONE);
>        |                                    ~^            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>        |                                     |                             |
>        |                                     unsigned int                  long unsigned int
>        |                                    %lu
> block/blk-iocost.c: In function ‘ioc_weight_show’:
> block/blk-iocost.c:3045:34: error: format ‘%u’ expects argument of type ‘unsigned int’, but argument 3 has type ‘long unsigned int’ [-Werror=format=]
>   3045 |         seq_printf(sf, "default %u\n", iocc->dfl_weight / WEIGHT_ONE);
>        |                                 ~^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>        |                                  |                      |
>        |                                  unsigned int           long unsigned int
>        |                                 %lu

But introduces two with gcc-12 ;):
 > block/blk-iocost.c: In function ‘ioc_weight_prfill’:
 > block/blk-iocost.c:3037:38: error: format ‘%lu’ expects argument of 
type ‘long unsigned int’, but argument 4 has type ‘u32’ {aka ‘unsigned 
int’} [-Werror=format=]
 >  3037 |                 seq_printf(sf, "%s %lu\n", dname, 
iocg->cfg_weight / WEIGHT_ONE);
 >       |                                    ~~^ 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 >       |                                      | 
      |
 >       |                                      long unsigned int 
      u32 {aka unsigned int}
 >       |                                    %u


Note that:
1) the specs says enum behaves as int, or uint in some cases
2) iocc->dfl_weight is u32, i.e. uint
    WEIGHT_ONE is 1 << 16, i.e. int
    so the promotion should be to s32/int. Or not?

I think gcc-13 is wrong -- incosistent with gcc-12 at least.

> Signed-off-by: Martin Liska <mliska@...e.cz>
> ---
>   block/blk-iocost.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-iocost.c b/block/blk-iocost.c
> index 495396425bad..f165bac9bffb 100644
> --- a/block/blk-iocost.c
> +++ b/block/blk-iocost.c
> @@ -3032,7 +3032,7 @@ static u64 ioc_weight_prfill(struct seq_file *sf, struct blkg_policy_data *pd,
>   	struct ioc_gq *iocg = pd_to_iocg(pd);
>   
>   	if (dname && iocg->cfg_weight)
> -		seq_printf(sf, "%s %u\n", dname, iocg->cfg_weight / WEIGHT_ONE);
> +		seq_printf(sf, "%s %lu\n", dname, iocg->cfg_weight / WEIGHT_ONE);
>   	return 0;
>   }
>   
> @@ -3042,7 +3042,7 @@ static int ioc_weight_show(struct seq_file *sf, void *v)
>   	struct blkcg *blkcg = css_to_blkcg(seq_css(sf));
>   	struct ioc_cgrp *iocc = blkcg_to_iocc(blkcg);
>   
> -	seq_printf(sf, "default %u\n", iocc->dfl_weight / WEIGHT_ONE);
> +	seq_printf(sf, "default %lu\n", iocc->dfl_weight / WEIGHT_ONE);
>   	blkcg_print_blkgs(sf, blkcg, ioc_weight_prfill,
>   			  &blkcg_policy_iocost, seq_cft(sf)->private, false);
>   	return 0;

thanks,
-- 
js
suse labs