Date: Sat, 14 Feb 2015 23:44:20 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Bruce Evans <brde@optusnet.com.au> Cc: src-committers@freebsd.org, Ian Lepore <ian@freebsd.org>, svn-src-all@freebsd.org, Pedro Giffuni <pfg@freebsd.org>, Gleb Smirnoff <glebius@freebsd.org>, svn-src-head@freebsd.org Subject: Re: svn commit: r278737 - head/usr.sbin/flowctl Message-ID: <20150215074419.GB1953@funkthat.com> In-Reply-To: <20150215162553.L977@besplex.bde.org> References: <201502132357.t1DNvKda075915@svn.freebsd.org> <20150214193210.N945@besplex.bde.org> <20150214181508.GL15484@FreeBSD.org> <1423938828.80968.148.camel@freebsd.org> <54DFA7CC.20305@FreeBSD.org> <20150215162553.L977@besplex.bde.org>
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Bruce Evans wrote this message on Sun, Feb 15, 2015 at 17:53 +1100:
> On Sat, 14 Feb 2015, Pedro Giffuni wrote:
>
> > On 02/14/15 13:33, Ian Lepore wrote:
> >> On Sat, 2015-02-14 at 21:15 +0300, Gleb Smirnoff wrote:
> >>> 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?
Could this just be changed to something like:
struct ng_mesg ng_mesg[(SORCVBUF_SIZE + sizeof(struct ng_mesg) - 1) /
sizeof(struct ng_mesg)];
It might allocate a few extra bytes, but no more than 55, and gets
alignment correct w/o lots of other hacks...
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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