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Date: Sat, 14 Feb 2015 21:15:08 +0300
From: Gleb Smirnoff <glebius@FreeBSD.org>
To: Bruce Evans <brde@optusnet.com.au>
Subject: Re: svn commit: r278737 - head/usr.sbin/flowctl
Message-ID: <20150214181508.GL15484@FreeBSD.org>
References: <201502132357.t1DNvKda075915@svn.freebsd.org>
 <20150214193210.N945@besplex.bde.org>
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  Bruce,

On Sat, Feb 14, 2015 at 08:46:58PM +1100, Bruce Evans wrote:
B> Using VLAs and also the C99 feature of declarations anwhere, and extensions
B> like __aligned(), we can almost implement a full alloca() using the fixed
B> version of this change:
B> 
B> /*
B>   * XXX need extended statement-expression so that __buf doesn't go out
B>   * of scope after the right brace.
B>   */
B> #define	my_alloca(n) __extension__ ({
B>  	/* XXX need unique name. */				\
B>  	char __buf[__roundup2((n), MUMBLE)] __aligned(MUMBLE);	\
B>  								\
B>  	(void *)__buf;						\
B> })

I like this idea. But would this exact code work? The life of
__buf is limited by the code block, and we exit the block
immediately. Wouldn't the allocation be overwritten if we
enter any function or block later?

-- 
Totus tuus, Glebius.