linux-kernel - Re: [RFC PATCH v1 5/6] tools/nolibc/stdlib: Implement `malloc()`, `calloc()`, `realloc()` and `free()`

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Date:   Sun, 20 Mar 2022 17:16:44 +0100
From:   Willy Tarreau <w@....eu>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Alviro Iskandar Setiawan <alviro.iskandar@...weeb.org>,
        Nugraha <richiisei@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>
Subject: Re: [RFC PATCH v1 5/6] tools/nolibc/stdlib: Implement `malloc()`,
 `calloc()`, `realloc()` and `free()`

Ammar,

a few points below:

On Sun, Mar 20, 2022 at 04:37:49PM +0700, Ammar Faizi wrote:
> +struct nolibc_heap {
> +	size_t	len;
> +	char	user_p[] __attribute__((__aligned__));
> +};

Note that many programs assume that malloc() returns a field aligned
to 2*sizeof(pointer) and unless I'm mistaken, above the user pointer
will only be aligned by one pointer. This may have an impact when the
compiler decides to use SIMD instructions.

> +#ifndef offsetof
> +#define offsetof(TYPE, FIELD) ((size_t) &((TYPE *)0)->FIELD)
> +#endif
> +
> +#ifndef container_of
> +#define container_of(PTR, TYPE, FIELD) ({			\
> +	__typeof__(((TYPE *)0)->FIELD) *__FIELD_PTR = (PTR);	\
> +	(TYPE *)((char *) __FIELD_PTR - offsetof(TYPE, FIELD));	\
> +})
> +#endif

These ones are independent on the malloc code and should move to a
different patch and likely to a different file. I'm seeing we already
have a few macros in types.h and since it's shared by almost everything
it might be more suitable there.

Thanks!
Willy