From: Matthias Urlichs <smurf@smurf.noris.de>
To: linux-kernel@vger.kernel.org
Subject: Re: p = kmalloc(sizeof(*p), )
Date: Mon, 19 Sep 2005 23:20:02 +0200 [thread overview]
Message-ID: <pan.2005.09.19.21.19.59.501960@smurf.noris.de> (raw)
In-Reply-To: Pine.LNX.4.58.0509181513440.9106@g5.osdl.org
Hi, Linus Torvalds wrote:
> Well, to be slightly more positive: it's not a very easy feature to do
> properly.
It's apparently an easy feature to do decidedly suboptimally.
This sample code
#include <malloc.h>
struct foo {
char fill1[1000];
int bar;
char fill2[1000];
int baz;
char fill3[1000];
};
struct foo *get_foo() {
struct foo *res = malloc(sizeof(struct foo));
*res = (struct foo){.bar=5, .baz=7};
return res;
}
calls memcpy _twice_ -- it initializes the object on the stack from a
couple of mostly-zero bytes in .rodata, and then memcpy's the thing to the
heap.
> So considering that almost nobody does this (certainly not SpecInt), and
> it would probably require re-organizations at many levels, I'm not
> surprised it hasn't gotten a lot of attention.
>
This is gcc 4.0. Optimization levels (I tried 0, 3, and s) don't affect
this -- which surprised me; I'd have thought that gcc would decide on
the proper trade-off between programmed and static initialization a bit
later.
--
Matthias Urlichs | {M:U} IT Design @ m-u-it.de | smurf@smurf.noris.de
Disclaimer: The quote was selected randomly. Really. | http://smurf.noris.de
- -
O that my tongue were in the thunder's mouth! Then with a passion would I
shake the world.
-- Shakespeare
next prev parent reply other threads:[~2005-09-19 21:24 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-09-18 10:06 p = kmalloc(sizeof(*p), ) Russell King
2005-09-18 11:04 ` Alan Cox
2005-09-18 14:39 ` Al Viro
2005-09-18 16:25 ` Denis Vlasenko
2005-09-18 17:30 ` Al Viro
2005-09-18 18:00 ` Willy Tarreau
2005-09-18 17:47 ` Alan Cox
2005-09-18 16:32 ` Robert Love
2005-09-18 16:52 ` Willy Tarreau
2005-09-18 17:18 ` Al Viro
2005-09-18 17:31 ` Linus Torvalds
2005-09-18 17:45 ` Al Viro
2005-09-18 20:34 ` Roman Zippel
2005-09-18 21:12 ` Al Viro
2005-09-18 21:52 ` Al Viro
2005-09-18 22:25 ` Linus Torvalds
2005-09-18 23:07 ` Al Viro
2005-09-20 6:31 ` Richard Henderson
2005-09-19 21:20 ` Matthias Urlichs [this message]
2005-09-19 21:28 ` Matthias Urlichs
2005-09-18 19:07 ` Al Viro
2005-09-18 21:30 ` Alan Cox
2005-09-18 21:14 ` Al Viro
2005-09-19 6:09 ` Coywolf Qi Hunt
2005-09-21 2:18 ` Miles Bader
2005-09-18 17:32 ` Randy.Dunlap
2005-09-19 6:47 ` Coywolf Qi Hunt
2005-09-20 8:53 ` Pekka Enberg
2005-09-20 9:39 ` Al Viro
2005-09-20 9:47 ` Pekka J Enberg
2005-09-20 9:53 ` Al Viro
2005-09-20 10:07 ` Pekka J Enberg
2005-09-20 15:14 ` Randy.Dunlap
2005-09-20 11:18 ` Pekka Enberg
2005-09-20 11:40 ` Russell King
2005-09-20 11:56 ` Denis Vlasenko
2005-09-20 12:20 ` Pekka J Enberg
2005-09-20 12:31 ` Russell King
2005-09-20 12:35 ` Pekka J Enberg
2005-09-20 15:21 ` Randy.Dunlap
2005-09-20 12:53 ` Pekka J Enberg
2005-09-20 17:11 ` Andrew Morton
2005-09-20 17:17 ` Russell King
2005-09-20 18:02 ` Alan Cox
2005-09-20 17:59 ` Andrew Morton
2005-09-20 18:11 ` Russell King
2005-09-20 18:41 ` Jeff Garzik
2005-09-20 20:41 ` Alan Cox
2005-09-20 19:41 ` Horst von Brand
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