linux-kernel - Re: [PATCH 6/7] bcachefs: Fix -Wcompare-distinct-pointer-types in do

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Message-ID: <20230913215901.kffbnpkosg7pkxd6@google.com>
Date:   Wed, 13 Sep 2023 21:59:01 +0000
From:   Justin Stitt <justinstitt@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     kent.overstreet@...ux.dev, bfoster@...hat.com,
        linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, patches@...ts.linux.dev
Subject: Re: [PATCH 6/7] bcachefs: Fix -Wcompare-distinct-pointer-types in
 do_encrypt()

On Tue, Sep 12, 2023 at 12:15:43PM -0700, Nathan Chancellor wrote:
> When building bcachefs for 32-bit ARM, there is a warning when using
> min() to compare a variable of type 'size_t' with an expression of type
> 'unsigned long':
>
>   fs/bcachefs/checksum.c:142:22: error: comparison of distinct pointer types ('typeof (len) *' (aka 'unsigned int *') and 'typeof (((1UL) << 12) - offset) *' (aka 'unsigned long *')) [-Werror,-Wcompare-distinct-pointer-types]
>     142 |                         unsigned pg_len = min(len, PAGE_SIZE - offset);
>         |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   include/linux/minmax.h:69:19: note: expanded from macro 'min'
>      69 | #define min(x, y)       __careful_cmp(x, y, <)
>         |                         ^~~~~~~~~~~~~~~~~~~~~~
>   include/linux/minmax.h:38:24: note: expanded from macro '__careful_cmp'
>      38 |         __builtin_choose_expr(__safe_cmp(x, y), \
>         |                               ^~~~~~~~~~~~~~~~
>   include/linux/minmax.h:28:4: note: expanded from macro '__safe_cmp'
>      28 |                 (__typecheck(x, y) && __no_side_effects(x, y))
>         |                  ^~~~~~~~~~~~~~~~~
>   include/linux/minmax.h:22:28: note: expanded from macro '__typecheck'
>      22 |         (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
>         |                    ~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~
>   1 error generated.
>
> On 64-bit architectures, size_t is 'unsigned long', so there is no
> warning when comparing these two expressions. Use min_t(size_t, ...) for
> this situation, eliminating the warning.
>
> Fixes: 1fb50457684f ("bcachefs: Fix memory corruption in encryption path")
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
Reviewed-by: Justin Stitt <justinstitt@...gle.com>

> ---
>  fs/bcachefs/checksum.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/bcachefs/checksum.c b/fs/bcachefs/checksum.c
> index 36939020f67d..ff0c3cd39ee2 100644
> --- a/fs/bcachefs/checksum.c
> +++ b/fs/bcachefs/checksum.c
> @@ -139,7 +139,7 @@ static inline int do_encrypt(struct crypto_sync_skcipher *tfm,
>
>  		for (i = 0; i < pages; i++) {
>  			unsigned offset = offset_in_page(buf);
> -			unsigned pg_len = min(len, PAGE_SIZE - offset);
> +			unsigned pg_len = min_t(size_t, len, PAGE_SIZE - offset);
>
>  			sg_set_page(sg + i, vmalloc_to_page(buf), pg_len, offset);
>  			buf += pg_len;
>
> --
> 2.42.0
>