[LEDE-DEV] [PATCH] libubox: Fix calloc_a() to return mem aligned pointers

[Yousong Zhou]

On 24 February 2017 at 05:20, Ted Hess <thess at kitschensync.net> wrote:
> The current implementation of calloc_a() returns packed pointers for the extra
> arguments. These packed, unaligned, pointers are OK for a lot of architectures,
> but not all. This patch will aligned the pointers returned in a manner congruent
> with malloc(). I do not believe the extra padding overhead is all the burdensome
> considering the overhead of separate malloc/calloc/free call to accomplish the
> same thing.
>
>
> Signed-off-by: Ted Hess <thess at kitschensync.net>
> ---
>  utils.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/utils.c b/utils.c
> index 5d9d5aa..314f716 100644
> --- a/utils.c
> +++ b/utils.c
> @@ -27,6 +27,9 @@
>                 _addr; \
>                 _addr = va_arg(_arg, void **), _len = _addr ? va_arg(_arg,
> size_t) : 0)
>
> +#define C_PTR_ALIGN    (2*sizeof(size_t))
> +#define C_PTR_MASK     (-C_PTR_ALIGN)
> +

sizeof(long) should be used for C_PTR_ALIGN, though I cannot find the
quote at the moment...

                yousong

>  void *__calloc_a(size_t len, ...)
>  {
>         va_list ap, ap1;
> @@ -40,7 +43,7 @@ void *__calloc_a(size_t len, ...)
>
>         va_copy(ap1, ap);
>         foreach_arg(ap1, cur_addr, cur_len, &ret, len)
> -               alloc_len += cur_len;
> +               alloc_len += (cur_len + C_PTR_ALIGN - 1 ) & C_PTR_MASK;
>         va_end(ap1);
>
>         ptr = calloc(1, alloc_len);
> @@ -49,7 +52,7 @@ void *__calloc_a(size_t len, ...)
>         alloc_len = 0;
>         foreach_arg(ap, cur_addr, cur_len, &ret, len) {
>                 *cur_addr = &ptr[alloc_len];
> -               alloc_len += cur_len;
> +               alloc_len += (cur_len + C_PTR_ALIGN - 1) & C_PTR_MASK;
>         }
>         va_end(ap);
>
> --
> 2.7.4
>
>
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