Re: somebody dropped a (warning) bomb

J.A. Magallón
2007-02-09T00:03:38Z

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
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