Date: Mon, 31 Oct 2005 15:42:54 +0300 From: Igor Robul <igorr@speechpro.com> To: Rob <spamrefuse@yahoo.com>, freebsd-questions@freebsd.org Subject: dlopen()/dlsym()/dlerror() was: Re: libXcursor.so.1.0.2 reference in libX11.so.6 ?? Message-ID: <4366114E.2060907@speechpro.com> In-Reply-To: <20051031114230.57427.qmail@web36212.mail.mud.yahoo.com> References: <20051031114230.57427.qmail@web36212.mail.mud.yahoo.com>
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Rob wrote:
>>
>>So you can see, from where we got 1.0.2
>>
>>
>>
>
>
>Yes, indeed, very true.
>It's Xorg that has this library version hardcoded.
>
>Meanwhile, I also found out following:
>
>On FreeBSD, the dl* functions do not reset a
>previous error indicator. In this specific case,
>in xc/lib/X11/CrGlCur.c Xorg will first try to
>"dlopen" the library libXcursor.so.1.0.2 without
>success (this will set the dlerror indicator),
>next Xorg will try to dlopen libXcursor.so.1.0
>without success (again sets dlerror indicator), but
>eventually successfully dlopens libXcursor.so.1.
>However, the last successful dlopen call does NOT
>clear the earlier dlerror indicator.
>
>
dlerror() resets error indicator. From /usr/src/libexec/rtld-elf/rtld.c:
const char *
dlerror(void)
{
char *msg = error_message;
error_message = NULL;
return msg;
}
Error indicator is not reseted by successful call to dlopen(), but I'm
not sure that dlopen() need reset error
indicator. At least I could not find information about this in manual page.
>Conclusively:
>The whole library problem boils down to the
>behaviour of the dl* functions, with respect to
>the clearing/setting the dlerror indicator.
>In general, one should always call dlerror() prior
>to the use of the dl* functions, to clear any
>previous dlerror indicator:
>
> dlerror(); /* clear previous error*/
>
> handle = dlopen("blabla.lib", RTLD_LAZY)
> if ( !handle ) {
> error_print(dlerror());
> return FAILURE;
> }
>
> data = dlsym(....);
> error = dlerror();
> if ( !data && error != NULL ) {
> error_print(error);
> return FAILURE;
> }
>
> etc. etc.
>
>Note that a dlerror() call always will clear any
>previous dlerror indicator.
>
>Does all that make sense to you?
>
>
Yes.
Is there any standart which describes dl*() functions? Because from _my_
point of view
dlopen()/dlsym() need not clear error indicator on success,
dlopen()/dlsym() need to return NULL
on error. dlerror() is one who can/have to clear error indicator.
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