Re: [PATCH] tools: usb: ffs-test: read the descriptor counts with unaligned accesses

[Michał Nazarewicz]

On Sun, Oct 11 2026, Sasha Levin wrote:
> descs_to_legacy() reads the descriptor counts through a __le32 pointer
> taken from a member of a packed struct, which may be unaligned:
>
>   ffs-test.c:235:40: warning: taking address of packed member of 'struct <anonymous>' may result in an unaligned pointer value [-Waddress-of-packed-member]
>
> Walk the counts with a byte pointer and get_unaligned_le32().
>
> Fixes: b9a4274699c69 ("tools: ffs-test: add compatibility code for old kernels")
> Assisted-by: LLM
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  tools/usb/ffs-test.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/tools/usb/ffs-test.c b/tools/usb/ffs-test.c
> index 22b938fbdfb77..f08060459b3f1 100644
> --- a/tools/usb/ffs-test.c
> +++ b/tools/usb/ffs-test.c
> @@ -232,7 +232,8 @@ static size_t descs_to_legacy(void **legacy, const void *descriptors_v2)
>  			const struct usb_functionfs_descs_head_v2 header;
>  			const __le32 counts[];
>  		} __attribute__((packed)) *const in = descriptors_v2;
> -		const __le32 *counts = in->counts;
> +		const unsigned char *counts =
> +			(const unsigned char *)descriptors_v2 + sizeof(in->header);

Why not:

+		const unsigned char *counts = (const void*)in->counts;

Or maybe change the structure to `const unsigned char counts[4][]` and
the variable `const unsigned char (*counts)[4]`?

>  		__u32 flags;
>  
>  		if (le32_to_cpu(in->header.magic) !=
> @@ -252,9 +253,9 @@ static size_t descs_to_legacy(void **legacy, const void *descriptors_v2)
>  				break;			\
>  			if (length < 4)			\
>  				return 0;		\
> -			ret = le32_to_cpu(*counts);	\
> +			ret = get_unaligned_le32(counts); \
>  			length -= 4;			\
> -			++counts;			\
> +			counts += 4;			\
>  		} while (0)
>  
>  		GET_NEXT_COUNT_IF_FLAG(fs_count, FUNCTIONFS_HAS_FS_DESC);

-- 
Best regards
ミハウ “𝓶𝓲𝓷𝓪86” ナザレヴィツ
«If at first you don’t succeed, give up skydiving»