Re: [PATCH 01/16] eal: add function attributes for allocation functions

[David Marchand <david.marchand@redhat.com>]

On Fri, Sep 27, 2024 at 4:48 PM Stephen Hemminger
<stephen@networkplumber.org> wrote:
>
> The allocation functions take a alignment argument that
> can be useful to hint the compiler optimizer.
>
> This is supported by Gcc and Clang but only useful with
> Gcc because Clang gives warning if alignment is 0.
>
> Recent versions of GCC have a malloc attribute that can
> be used to find mismatches between allocation and free;
> the typical problem caught is a pointer allocated with
> rte_malloc() that is then incorrectly freed using free().

Interesting tool.

>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>  lib/eal/include/rte_common.h | 30 ++++++++++++++++++++++++++++++
>  lib/eal/include/rte_malloc.h | 24 ++++++++++++++++--------
>  2 files changed, 46 insertions(+), 8 deletions(-)
>
> diff --git a/lib/eal/include/rte_common.h b/lib/eal/include/rte_common.h
> index eec0400dad..1b3781274d 100644
> --- a/lib/eal/include/rte_common.h
> +++ b/lib/eal/include/rte_common.h
> @@ -228,6 +228,36 @@ typedef uint16_t unaligned_uint16_t;
>  #define __rte_alloc_size(...)
>  #endif
>
> +/**
> + * Tells the compiler that the function returns a value that points to
> + * memory aligned by a function argument.
> + * Not enabled on clang because it warns if align argument is zero.
> + */
> +#if defined(RTE_CC_GCC)
> +#define __rte_alloc_align(align_arg) \
> +       __attribute__((alloc_align(align_arg)))
> +#else
> +#define __rte_alloc_align(...)
> +#endif
> +
> +/**
> + * Tells the compiler this is a function like malloc and that the pointer
> + * returned cannot alias any other pointer (ie new memory).
> + *
> + * Also, with recent GCC versions also able to track that proper
> + * dealloctor function is used for this pointer.
> + */
> +#if defined(RTE_TOOLCHAIN_GCC) && (GCC_VERSION >= 110000)

Even though it is probably equivalent, GCC_VERSION is set with RTE_CC_GCC.

> +#define __rte_alloc_func(free_func) \
> +       __attribute__((malloc, malloc(free_func)))

I read that this malloc attribute can also make use of the arg index
to assume the pointer is freed.

Did you try this feature?

Something like:

@@ -248,14 +248,13 @@ typedef uint16_t unaligned_uint16_t;
  * dealloctor function is used for this pointer.
  */
 #if defined(RTE_TOOLCHAIN_GCC) && (GCC_VERSION >= 110000)
-#define __rte_alloc_func(free_func) \
-       __attribute__((malloc, malloc(free_func)))
-
+#define __rte_alloc_func(...) \
+       __attribute__((malloc, malloc(__VA_ARGS__)))
 #elif defined(RTE_CC_GCC) || defined(RTE_CC_CLANG)
-#define __rte_alloc_func(free_func) \
+#define __rte_alloc_func(...) \
        __attribute__((malloc))
 #else
-#define __rte_alloc_func(free_func)
+#define __rte_alloc_func(...)
 #endif

 #define RTE_PRIORITY_LOG 101

> +
> +#elif defined(RTE_CC_GCC) || defined(RTE_CC_CLANG)
> +#define __rte_alloc_func(free_func) \
> +       __attribute__((malloc))
> +#else
> +#define __rte_alloc_func(free_func)
> +#endif
> +
>  #define RTE_PRIORITY_LOG 101
>  #define RTE_PRIORITY_BUS 110
>  #define RTE_PRIORITY_CLASS 120


-- 
David Marchand