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

[Ted Hess]

-----Original Message----- 
From: Yousong Zhou
Sent: Thursday, February 23, 2017 7:15 PM
To: Ted Hess
Cc: lede-dev
Subject: Re: [LEDE-DEV] [PATCH] libubox: Fix calloc_a() to return mem aligned pointers

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

I picked the expression from malloc in the musl sources. No hard preferences, but it does do proper alignment for 64-bit systems and 
other sensitive data-types AFAICT.

/ted