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From: "J.A. Magallón" <jamagallon@ono.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jan Engelhardt <jengelh@linux01.gwdg.de>,
	Jeff Garzik <jeff@garzik.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: somebody dropped a (warning) bomb
Date: Fri, 9 Feb 2007 01:03:17 +0100	[thread overview]
Message-ID: <20070209010317.3c442240@werewolf-wl> (raw)
In-Reply-To: <Pine.LNX.4.64.0702081351410.8424@woody.linux-foundation.org>

On Thu, 8 Feb 2007 14:03:06 -0800 (PST), Linus Torvalds <torvalds@linux-foundation.org> wrote:

> 
> 
> On Thu, 8 Feb 2007, Linus Torvalds wrote:
> > 
> > But THE CALLER CANNOT AND MUST NOT CARE! Because the sign of "char" is 
> > implementation-defined, so if you call "strcmp()", you are already 
> > basically saying: I don't care (and I _cannot_ care) what sign you are 
> > using.
> 
> Let me explain it another way.
> 
> Say you use
> 
> 	signed char *myname, *yourname;
> 
> 	if (strcmp(myname,yourname) < 0)
> 		printf("Ha, I win!\n")
> 
> and you compile this on an architecture where "char" is signed even 
> without the explicit "signed".
> 
> What should happen?
> 
> Should you get a warning? The types really *are* the same, so getting a 
> warning sounds obviously insane. But on the other hand, if you really care 
> about the sign that strcmp() uses internally, the code is wrong *anyway*, 

Thats the point. Mmmm, I think I see it the other way around. I defined
a variable as 'signed' or 'unsigned', because the sign info matters for me.
And gcc warns about using a function on it that will _ignore_ or even
misinterpret that info. Could it be a BUG ? Yes.

> because with another compiler, or with the *same* compiler on another 
> architecture or some other compiler flags, the very same code is buggy.
> 
> In other words, either you should get a warning *regardless* of whether 
> the sign actually matches or not, or you shouldn't get a warning at all 
> for the above code. Either it's buggy code, or it isn't.
> 

In fact, I tried to look for an arch where this gives only _one_ error:

#include <string.h>

void f()
{
	const unsigned char *a;
	const signed char *b;

	int la,lb;

	la = strlen(a);
	lb = strlen(b);
}

and guess, all give _both_ errors.

Linux/x86, gcc 4.1.2-0.20070115:
werewolf:~> gcc -Wpointer-sign -c t.c
t.c: In function ‘f’:
t.c:10: warning: pointer targets in passing argument 1 of ‘strlen’ differ in signedness
t.c:11: warning: pointer targets in passing argument 1 of ‘strlen’ differ in signedness

OSX ppc, gcc-4.0.1
belly:~> gcc -Wpointer-sign -c t.c
t.c: In function ‘f’:
t.c:10: warning: pointer targets in passing argument 1 of ‘strlen’ differ in signedness
t.c:11: warning: pointer targets in passing argument 1 of ‘strlen’ differ in signedness

Solaris5.7 Ultra, cc WorkShop Compilers 5.0
den:~> cc -Xa -c t.c                                                           
ucbcc: Warning: "-Xa" redefines compatibility mode from "SunC transition" to "ANSI"
"t.c", line 10: warning: argument #1 is incompatible with prototype:
        prototype: pointer to const char : "/usr/include/string.h", line 71
        argument : pointer to const uchar
"t.c", line 11: warning: argument #1 is incompatible with prototype:
        prototype: pointer to const char : "/usr/include/string.h", line 71
        argument : pointer to const schar

This makes sense.
Someone can try on something psychedelic, like ARM ;) ?

--
J.A. Magallon <jamagallon()ono!com>     \               Software is like sex:
                                         \         It's better when it's free
Mandriva Linux release 2007.1 (Cooker) for i586
Linux 2.6.19-jam06 (gcc 4.1.2 20070115 (prerelease) (4.1.2-0.20070115.1mdv2007.1)) #1 SMP PREEMPT

  parent reply	other threads:[~2007-02-09  0:03 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-08 15:00 Jeff Garzik
2007-02-08 16:33 ` Linus Torvalds
2007-02-08 18:42   ` Jan Engelhardt
2007-02-08 19:53     ` Linus Torvalds
2007-02-08 21:10       ` Jan Engelhardt
2007-02-08 21:37         ` Linus Torvalds
2007-02-08 23:12           ` David Rientjes
2007-02-08 23:37             ` Linus Torvalds
2007-02-09  0:24               ` David Rientjes
2007-02-09  0:42                 ` Linus Torvalds
2007-02-09  0:59                   ` Linus Torvalds
2007-02-09  0:59                   ` David Rientjes
2007-02-09  1:11                     ` Linus Torvalds
2007-02-09  1:18                       ` David Rientjes
2007-02-09 15:38                         ` Linus Torvalds
2007-02-09  3:27                   ` D. Hazelton
2007-02-09 19:54                     ` Pete Zaitcev
2007-02-09 12:34                   ` Jan Engelhardt
2007-02-09 13:16                     ` linux-os (Dick Johnson)
2007-02-09 17:45                       ` Jan Engelhardt
2007-02-09 20:29                         ` linux-os (Dick Johnson)
2007-02-09 22:05                           ` Jan Engelhardt
2007-02-09 22:58                             ` Martin Mares
2007-02-12 18:50                             ` linux-os (Dick Johnson)
2007-02-13 15:14                     ` Dick Streefland
2007-02-08 21:13       ` J.A. Magallón
2007-02-08 21:42         ` Linus Torvalds
2007-02-08 22:03           ` Linus Torvalds
2007-02-08 22:19             ` Willy Tarreau
2007-02-09  0:03             ` J.A. Magallón [this message]
2007-02-09  0:22               ` Linus Torvalds
2007-02-09 12:38             ` Sergei Organov
2007-02-09 15:58               ` Linus Torvalds
2007-02-12 11:12                 ` Sergei Organov
2007-02-12 16:26                   ` Linus Torvalds
2007-02-13 18:06                     ` Sergei Organov
2007-02-13 18:26                       ` Pekka Enberg
2007-02-13 19:14                         ` Sergei Organov
2007-02-13 19:43                           ` Pekka Enberg
2007-02-13 20:29                             ` Sergei Organov
2007-02-13 21:31                               ` Jeff Garzik
2007-02-13 23:21                               ` Linus Torvalds
2007-02-15 13:20                                 ` Sergei Organov
2007-02-15 15:57                                   ` Linus Torvalds
2007-02-15 18:53                                     ` Sergei Organov
2007-02-15 19:02                                       ` Linus Torvalds
2007-02-15 20:23                                         ` me, not " Oleg Verych
2007-02-16  4:26                                         ` Rene Herman
2007-02-19 11:58                                           ` Sergei Organov
2007-02-19 13:58                                         ` Sergei Organov
2007-02-15 22:32                                     ` Lennart Sorensen
2007-02-13 19:25                       ` Linus Torvalds
2007-02-13 19:59                         ` Sergei Organov
2007-02-13 20:24                           ` Linus Torvalds
2007-02-15 15:15                             ` Sergei Organov
2007-02-13 21:13                         ` Rob Landley
2007-02-13 22:21                       ` Olivier Galibert
2007-02-14 12:52                         ` Sergei Organov
2007-02-15 20:06                         ` Sergei Organov
2007-02-09 15:10     ` Sergei Organov
2007-02-08 16:35 ` Kumar Gala
     [not found] <7Mj5f-3oz-21@gated-at.bofh.it>
     [not found] ` <7MktH-5EW-35@gated-at.bofh.it>
     [not found]   ` <7Mmvy-vj-17@gated-at.bofh.it>
     [not found]     ` <7MnBC-2fk-13@gated-at.bofh.it>
     [not found]       ` <7MoQx-4p8-11@gated-at.bofh.it>
     [not found]         ` <7MpjE-50z-7@gated-at.bofh.it>
     [not found]           ` <7MpCS-5Fe-9@gated-at.bofh.it>
     [not found]             ` <7MDd7-17w-1@gated-at.bofh.it>
     [not found]               ` <7MGkB-62k-31@gated-at.bofh.it>
     [not found]                 ` <7NHoe-2Mb-37@gated-at.bofh.it>
     [not found]                   ` <7NMe9-1ZN-7@gated-at.bofh.it>
     [not found]                     ` <7Oagl-6bO-1@gated-at.bofh.it>
     [not found]                       ` <7ObvW-89N-23@gated-at.bofh.it>
     [not found]                         ` <7Oc8t-NS-1@gated-at.bofh.it>
2007-02-15 20:08                           ` Bodo Eggert
2007-02-16 11:21                             ` Sergei Organov
2007-02-16 14:51                               ` Bodo Eggert
2007-02-19 11:56                                 ` Sergei Organov
2007-02-16 12:46                             ` Sergei Organov
2007-02-16 17:40                               ` Bodo Eggert
2007-02-19 12:17                                 ` Sergei Organov

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