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From: Willy Tarreau <[email protected]>
To: Ammar Faizi <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>,
	Alviro Iskandar Setiawan <[email protected]>,
	Linux Kernel Mailing List <[email protected]>,
	GNU/Weeb Mailing List <[email protected]>,
	Facebook Kernel Team <[email protected]>
Subject: Re: [PATCH v1 1/2] tools/nolibc/stdlib: Support overflow checking for older compiler versions
Date: Fri, 20 May 2022 06:19:15 +0200	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

Hi Ammar,

On Fri, May 20, 2022 at 12:21:15AM +0700, Ammar Faizi wrote:
> diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h
> index 8fd32eaf8037..92378c4b9660 100644
> --- a/tools/include/nolibc/stdlib.h
> +++ b/tools/include/nolibc/stdlib.h
> @@ -128,10 +128,9 @@ void *malloc(size_t len)
>  static __attribute__((unused))
>  void *calloc(size_t size, size_t nmemb)
>  {
> -	void *orig;
> -	size_t res = 0;
> +	size_t x = size * nmemb;
>  
> -	if (__builtin_expect(__builtin_mul_overflow(nmemb, size, &res), 0)) {
> +	if (__builtin_expect(size && ((x / size) != nmemb), 0)) {

Ah, that approach is even better than mine, I'm seeing that on x86 the
compiler simply checks the overflow flag after the multiply, that's
perfect!

Acked-by: Willy Tarreau <[email protected]>

Willy

  reply	other threads:[~2022-05-20  4:19 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-19 17:21 [PATCH v1 0/2] nolibc updates for Linux 5.20 Ammar Faizi
2022-05-19 17:21 ` [PATCH v1 1/2] tools/nolibc/stdlib: Support overflow checking for older compiler versions Ammar Faizi
2022-05-20  4:19   ` Willy Tarreau [this message]
2022-05-20 11:29   ` Alviro Iskandar Setiawan
2022-05-20 17:32     ` Paul E. McKenney
2022-05-19 17:21 ` [PATCH v1 2/2] tools/nolibc/stdio: Add format attribute to enable printf warnings Ammar Faizi
2022-05-20  4:21   ` Willy Tarreau
2022-05-20  4:23 ` [PATCH v1 0/2] nolibc updates for Linux 5.20 Willy Tarreau

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