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

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

[Sasha Levin]

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@kernel.org>
---
 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);
 		__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);
-- 
2.53.0

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@kernel.org>
> ---
>  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»

[PATCH v2] tools: usb: ffs-test: read the descriptor counts with unaligned accesses

[Sasha Levin]

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@kernel.org>
---
Changes in v2:
- Take the byte pointer from in->counts instead of computing it from
  descriptors_v2 (Michał Nazarewicz)
- Link to v1: https://lore.kernel.org/r/20261011223445.2328181-1-sashal@kernel.org

 tools/usb/ffs-test.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/usb/ffs-test.c b/tools/usb/ffs-test.c
index 22b938fbdfb77..4453d810e9412 100644
--- a/tools/usb/ffs-test.c
+++ b/tools/usb/ffs-test.c
@@ -232,7 +232,7 @@ 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 void *)in->counts;
 		__u32 flags;
 
 		if (le32_to_cpu(in->header.magic) !=
@@ -252,9 +252,9 @@ 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);
-- 
2.53.0