Re: [PATCH] jfs: avoid -Wtautological-constant-out-of-range-compare warning

[Dave Kleikamp <dave.kleikamp@oracle.com>]

On 2/2/26 3:49AM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> A recent change for the range check started triggering a clang warning:
> 
> fs/jfs/jfs_dtree.c:2906:31: error: result of comparison of constant 128 with expression of type 's8' (aka 'signed char') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>   2906 |                         if (stbl[i] < 0 || stbl[i] >= DTPAGEMAXSLOT) {
>        |                                            ~~~~~~~ ^  ~~~~~~~~~~~~~
> fs/jfs/jfs_dtree.c:3111:30: error: result of comparison of constant 128 with expression of type 's8' (aka 'signed char') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>   3111 |                 if (stbl[0] < 0 || stbl[0] >= DTPAGEMAXSLOT) {
>        |                                    ~~~~~~~ ^  ~~~~~~~~~~~~~
> 
> Both the old and the new check were useless, but the previous version
> apparently did not lead to the warning.
> 
> Rephrase this again by adding a cast. The check is still always false,
> but the compiler shuts up about it.

I think it would be better to just drop the useless part of these tests.

Shaggy

> 
> Fixes: cafc6679824a ("jfs: replace hardcoded magic number with DTPAGEMAXSLOT constant")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>   fs/jfs/jfs_dtree.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/jfs/jfs_dtree.c b/fs/jfs/jfs_dtree.c
> index 0ab83bb7bbdf..e3301e5fa037 100644
> --- a/fs/jfs/jfs_dtree.c
> +++ b/fs/jfs/jfs_dtree.c
> @@ -2903,7 +2903,7 @@ int jfs_readdir(struct file *file, struct dir_context *ctx)
>   		stbl = DT_GETSTBL(p);
>   
>   		for (i = index; i < p->header.nextindex; i++) {
> -			if (stbl[i] < 0 || stbl[i] >= DTPAGEMAXSLOT) {
> +			if (stbl[i] < 0 || (unsigned char)stbl[i] >= DTPAGEMAXSLOT) {
>   				jfs_err("JFS: Invalid stbl[%d] = %d for inode %ld, block = %lld",
>   					i, stbl[i], (long)ip->i_ino, (long long)bn);
>   				free_page(dirent_buf);
> @@ -3108,7 +3108,7 @@ static int dtReadFirst(struct inode *ip, struct btstack * btstack)
>   		/* get the leftmost entry */
>   		stbl = DT_GETSTBL(p);
>   
> -		if (stbl[0] < 0 || stbl[0] >= DTPAGEMAXSLOT) {
> +		if (stbl[0] < 0 || (unsigned char)stbl[0] >= DTPAGEMAXSLOT) {
>   			DT_PUTPAGE(mp);
>   			jfs_error(ip->i_sb, "stbl[0] out of bound\n");
>   			return -EIO;