[PATCH 0/2][next] Add STACK_FLEX_ARRAY_SIZE() helper

[PATCH 0/2][next] Add STACK_FLEX_ARRAY_SIZE() helper

[Gustavo A. R. Silva]

Add new STACK_FLEX_ARRAY_SIZE() helper to get the size of a
flexible-array member defined using DEFINE_FLEX()/DEFINE_RAW_FLEX()
at compile time.

This is essentially the same as ARRAY_SIZE() but for on-stack
flexible-array members.

Gustavo A. R. Silva (2):
  overflow: Add STACK_FLEX_ARRAY_SIZE() helper
  kunit/overflow: Add tests for STACK_FLEX_ARRAY_SIZE() helper

 include/linux/overflow.h   | 13 +++++++++++++
 lib/tests/overflow_kunit.c |  3 +++
 2 files changed, 16 insertions(+)

-- 
2.43.0

[PATCH 1/2][next] overflow: Add STACK_FLEX_ARRAY_SIZE() helper

[Gustavo A. R. Silva]

Add new STACK_FLEX_ARRAY_SIZE() helper to get the size of a
flexible-array member defined using DEFINE_FLEX()/DEFINE_RAW_FLEX()
at compile time.

This is essentially the same as ARRAY_SIZE() but for on-stack
flexible-array members.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 include/linux/overflow.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 6ee67c20b575..5b2e0cc9aba2 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -420,6 +420,7 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
  * flexible array member.
  * Use __struct_size(@name) to get compile-time size of it afterwards.
  * Use __member_size(@name->member) to get compile-time size of @name members.
+ * Use STACK_FLEX_ARRAY_SIZE(@name, @member) to get compile-time size of array @member.
  */
 #define DEFINE_RAW_FLEX(type, name, member, count)	\
 	_DEFINE_FLEX(type, name, member, count, = {})
@@ -438,8 +439,20 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
  * flexible array member.
  * Use __struct_size(@NAME) to get compile-time size of it afterwards.
  * Use __member_size(@NAME->member) to get compile-time size of @NAME members.
+ * Use STACK_FLEX_ARRAY_SIZE(@name, @member) to get compile-time size of array @member.
  */
 #define DEFINE_FLEX(TYPE, NAME, MEMBER, COUNTER, COUNT)	\
 	_DEFINE_FLEX(TYPE, NAME, MEMBER, COUNT, = { .obj.COUNTER = COUNT, })
 
+/**
+ * STACK_FLEX_ARRAY_SIZE() - helper macro for DEFINE_FLEX() family.
+ * Returns the number of elements in @array.
+ *
+ * @name: Name for a variable defined in DEFINE_RAW_FLEX()/DEFINE_FLEX().
+ * @array: Name of the array member.
+ */
+#define STACK_FLEX_ARRAY_SIZE(name, array)						\
+	(__member_size((name)->array) / sizeof(*(name)->array) +			\
+						__must_be_array((name)->array))
+
 #endif /* __LINUX_OVERFLOW_H */
-- 
2.43.0

[PATCH 2/2][next] kunit/overflow: Add tests for STACK_FLEX_ARRAY_SIZE() helper

[Gustavo A. R. Silva]

Add a couple of tests for new STACK_FLEX_ARRAY_SIZE() helper.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 lib/tests/overflow_kunit.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/tests/overflow_kunit.c b/lib/tests/overflow_kunit.c
index 894691b4411a..3beb497a44be 100644
--- a/lib/tests/overflow_kunit.c
+++ b/lib/tests/overflow_kunit.c
@@ -1210,6 +1210,9 @@ static void DEFINE_FLEX_test(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, __struct_size(empty->array), 0);
 	KUNIT_EXPECT_EQ(test, __member_size(empty->array), 0);
 
+	KUNIT_EXPECT_EQ(test, STACK_FLEX_ARRAY_SIZE(two, array), 2);
+	KUNIT_EXPECT_EQ(test, STACK_FLEX_ARRAY_SIZE(eight, array), 8);
+
 	/* If __counted_by is not being used, array size will have the on-stack size. */
 	if (!IS_ENABLED(CONFIG_CC_HAS_COUNTED_BY))
 		array_size_override = 2 * sizeof(s16);
-- 
2.43.0

Re: [PATCH 1/2][next] overflow: Add STACK_FLEX_ARRAY_SIZE() helper

[Kees Cook]

On Tue, Apr 22, 2025 at 11:21:36AM -0600, Gustavo A. R. Silva wrote:
> Add new STACK_FLEX_ARRAY_SIZE() helper to get the size of a
> flexible-array member defined using DEFINE_FLEX()/DEFINE_RAW_FLEX()
> at compile time.
> 
> This is essentially the same as ARRAY_SIZE() but for on-stack
> flexible-array members.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
>  include/linux/overflow.h | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index 6ee67c20b575..5b2e0cc9aba2 100644
> --- a/include/linux/overflow.h
> +++ b/include/linux/overflow.h
> @@ -420,6 +420,7 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
>   * flexible array member.
>   * Use __struct_size(@name) to get compile-time size of it afterwards.
>   * Use __member_size(@name->member) to get compile-time size of @name members.
> + * Use STACK_FLEX_ARRAY_SIZE(@name, @member) to get compile-time size of array @member.

Instead of "size of" how about "number of elements in"

>   */
>  #define DEFINE_RAW_FLEX(type, name, member, count)	\
>  	_DEFINE_FLEX(type, name, member, count, = {})
> @@ -438,8 +439,20 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
>   * flexible array member.
>   * Use __struct_size(@NAME) to get compile-time size of it afterwards.
>   * Use __member_size(@NAME->member) to get compile-time size of @NAME members.
> + * Use STACK_FLEX_ARRAY_SIZE(@name, @member) to get compile-time size of array @member.

Same here.

>   */
>  #define DEFINE_FLEX(TYPE, NAME, MEMBER, COUNTER, COUNT)	\
>  	_DEFINE_FLEX(TYPE, NAME, MEMBER, COUNT, = { .obj.COUNTER = COUNT, })
>  
> +/**
> + * STACK_FLEX_ARRAY_SIZE() - helper macro for DEFINE_FLEX() family.
> + * Returns the number of elements in @array.

Which matches these docs.

> + *
> + * @name: Name for a variable defined in DEFINE_RAW_FLEX()/DEFINE_FLEX().
> + * @array: Name of the array member.
> + */
> +#define STACK_FLEX_ARRAY_SIZE(name, array)						\
> +	(__member_size((name)->array) / sizeof(*(name)->array) +			\
> +						__must_be_array((name)->array))
> +
>  #endif /* __LINUX_OVERFLOW_H */
> -- 
> 2.43.0
> 

-- 
Kees Cook

Re: [PATCH 2/2][next] kunit/overflow: Add tests for STACK_FLEX_ARRAY_SIZE() helper

[Kees Cook]

On Tue, Apr 22, 2025 at 11:22:08AM -0600, Gustavo A. R. Silva wrote:
> Add a couple of tests for new STACK_FLEX_ARRAY_SIZE() helper.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
>  lib/tests/overflow_kunit.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/lib/tests/overflow_kunit.c b/lib/tests/overflow_kunit.c
> index 894691b4411a..3beb497a44be 100644
> --- a/lib/tests/overflow_kunit.c
> +++ b/lib/tests/overflow_kunit.c
> @@ -1210,6 +1210,9 @@ static void DEFINE_FLEX_test(struct kunit *test)
>  	KUNIT_EXPECT_EQ(test, __struct_size(empty->array), 0);
>  	KUNIT_EXPECT_EQ(test, __member_size(empty->array), 0);
>  
> +	KUNIT_EXPECT_EQ(test, STACK_FLEX_ARRAY_SIZE(two, array), 2);
> +	KUNIT_EXPECT_EQ(test, STACK_FLEX_ARRAY_SIZE(eight, array), 8);

Nice! Can you add a 0 test for "empty" as well?

> +
>  	/* If __counted_by is not being used, array size will have the on-stack size. */
>  	if (!IS_ENABLED(CONFIG_CC_HAS_COUNTED_BY))
>  		array_size_override = 2 * sizeof(s16);
> -- 
> 2.43.0
> 

-- 
Kees Cook

Re: [PATCH 2/2][next] kunit/overflow: Add tests for STACK_FLEX_ARRAY_SIZE() helper

[Gustavo A. R. Silva]

On 22/04/25 14:39, Kees Cook wrote:
> On Tue, Apr 22, 2025 at 11:22:08AM -0600, Gustavo A. R. Silva wrote:
>> Add a couple of tests for new STACK_FLEX_ARRAY_SIZE() helper.
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>> ---
>>   lib/tests/overflow_kunit.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/lib/tests/overflow_kunit.c b/lib/tests/overflow_kunit.c
>> index 894691b4411a..3beb497a44be 100644
>> --- a/lib/tests/overflow_kunit.c
>> +++ b/lib/tests/overflow_kunit.c
>> @@ -1210,6 +1210,9 @@ static void DEFINE_FLEX_test(struct kunit *test)
>>   	KUNIT_EXPECT_EQ(test, __struct_size(empty->array), 0);
>>   	KUNIT_EXPECT_EQ(test, __member_size(empty->array), 0);
>>   
>> +	KUNIT_EXPECT_EQ(test, STACK_FLEX_ARRAY_SIZE(two, array), 2);
>> +	KUNIT_EXPECT_EQ(test, STACK_FLEX_ARRAY_SIZE(eight, array), 8);
> 
> Nice! Can you add a 0 test for "empty" as well?

Sure thing. I had actually added it, but for some reason I removed at the last
minute.

-Gustavo