From: bakul@bitblocks.com (Bakul Shah)
Subject: [TUHS] /bin/true (was basic tools / Universal Unix)
Date: Tue, 28 Nov 2017 10:34:13 -0800 [thread overview]
Message-ID: <20171128183428.A825F156E523@mail.bitblocks.com> (raw)
In-Reply-To: Your message of "Tue, 28 Nov 2017 10:56:52 -0700." <CANCZdfqwK1WT8FLJsJs6Eu9TqxABJzx4Nm7niHo3yxFtUk7+0A@mail.gmail.com>
On Tue, 28 Nov 2017 10:56:52 -0700 Warner Losh <imp at bsdimp.com> wrote:
Warner Losh writes:
>
> On Tue, Nov 28, 2017 at 9:21 AM, Nemo <cym224 at gmail.com> wrote:
>
> > A late comment: I seem to recall this boilerplate in earlier Solaris
> > but Solaris 10 has an executable. So I looked at the OpenSolaris
> > source out of curiosity and found this.
> >
> > [CDDL stuff here]
> > /*
> > * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
> > * Use is subject to license terms.
> > */
> >
> > #pragma ident "%Z%%M% %I% %E% SMI"
> >
> > #include <unistd.h>
> >
> > /*
> > * Exit with a zero value as quickly as possible.
> > */
> >
> > int
> > main(void)
> > {
> > _exit(0);
> > /*NOTREACHED*/
> > return (0);
> > }
> >
>
> Ah, the tyranny of static analysis tools... _exit(0) should be marked such
> that the tools know it does not return. This means the /*NOTREACHED*/ isn't
> needed. And since there's no real exit path out of main, the return (0) is
> equally bogus (because main can't return). Yet lint and other tools have
> ushered in this insanity.
>
> I'm glad to see these days that these sorts of lame false positives have
> been eliminated...
>
> Then again _exit(0) is a useless optimization. It saves three closes for
> files that are bound to be closed at image tear down. If it really is that
> important (absent data, my gut tells me it isn't), then this should be
> written in assembler. FreeBSD/amd64 would be something like:
>
> #include <sys/syscall.h>
> #include <machine/asm.h>
>
> ENTRY(_start)
> xor %r10, %r10
> mov $SYS_exit, %eax
> syscall
> END(_start)
>
> This some small hacks to each arch's SYS.h in libc, this could even be
> smaller and MI :). this is tiny:
> -rwxrwxr-x 1 imp imp 672 Nov 28 10:18 true
> text data bss dec hex filename
> 10 0 0 10 0xa true
>
> Contrast that with FreeBSD's /usr/bin/true:
> -r-xr-xr-x 1 root wheel 4624 Nov 20 11:56 /usr/bin/true
> text data bss dec hex filename
> 1540 481 8 2029 0x7ed /usr/bin/true
>
> which is little more than return(0), but also has a fair amount of
> copyright and SCCS data.
int main(void) { return 0; }
is sufficient for true. BTW this is pretty much what
/usr/src/usr.bin/true/true.c does.
And true can also be a file of length 0 chmoded to +x. No
need to optimize such things.
It should really be linked staticallly but crt1.o seems to
bring in the entire libc. I guess linking with just the things
a program needs is a hard problem!
next prev parent reply other threads:[~2017-11-28 18:34 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-19 14:52 /bin/true (was [TUHS] " Ron Natalie
2017-10-19 15:01 ` Pete Wright
2017-10-19 15:17 ` Chet Ramey
2017-10-19 21:23 ` Steffen Nurpmeso
2017-10-19 21:43 ` Chet Ramey
2017-10-19 23:00 ` [TUHS] /bin/true (was " Dave Horsfall
2017-10-19 23:14 ` Grant Taylor
2017-10-19 23:23 ` Lyndon Nerenberg
2017-10-19 23:27 ` Kurt H Maier
2017-10-22 4:18 ` Dave Horsfall
2017-10-20 12:10 ` Chet Ramey
2017-10-19 21:43 ` /bin/true (was [TUHS] " Dave Horsfall
2017-10-19 22:04 ` Ronald Natalie
2017-10-19 23:25 ` [TUHS] /bin/true (was " Dave Horsfall
[not found] ` <CAEoi9W7YZ7YXUip0JTMGip3Nd0czgdjqRCMRcK2GYmDJsckuDg@mail.gmail.com>
[not found] ` <CAEoi9W4zdJ3+RXjK5-5rAJ6rwx_0kx6N-bn1U61=txJGyLT_mw@mail.gmail.com>
2017-10-20 1:27 ` Dan Cross
2017-10-20 1:31 ` Lyndon Nerenberg
2017-10-20 2:05 ` Ronald Natalie
2017-11-28 16:21 ` Nemo
2017-11-28 17:56 ` Warner Losh
2017-11-28 18:26 ` Dan Cross
2017-11-28 18:41 ` Warner Losh
2017-11-28 19:09 ` Dan Cross
2017-11-28 20:34 ` Clem Cole
2017-11-28 22:42 ` Ralph Corderoy
2017-11-28 18:34 ` Bakul Shah [this message]
2017-11-28 23:25 ` Ralph Corderoy
2017-10-22 23:00 Doug McIlroy
2017-10-23 1:11 ` Dan Cross
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