[BRLTTY] dlsym/dlerror (was Re: Clumping all the braille driver modules into one big app?)

[Willie Walker]

Thanks Dave!  Given the below, this might actually turn into a one line 
fix to call dlerror() just before calling dlsym().  That should clear 
any existing error conditions and your existing code would continue to 
work, I think.

Will

Dave Mielke wrote:
> [quoted lines by Willie Walker on 2008/08/28 at 20:58 -0400]
> 
>> The problem is that brltty is jumping to dlerror too soon -- it should 
>> first check the result of dlsym.  The reason for this is that dlerror 
>> returns the message for the _last failed_ dlsym, not the result of the 
>> _last call_ to dlsym.  
> 
> There appears to be a philosophical difference between Solaris and Linux here. 
> The Linux man page for dlsym() says the following:
> 
>    Since the value of the symbol could actually be NULL (so that a NULL return 
>    from dlsym() need not indicate an error), the correct way to test for an 
>    error is to call dlerror() to clear any old error conditions, then call 
>    dlsym(), and then call dlerror() again, saving its return value into a 
>    variable, and check whether this saved value is not NULL.
> 
>> Internally, the Sun C library is doing some magic, which results in a 
>> caught/expected failure on the _ex_unwind symbol.  The change above checks the 
>> result of the call to dlsym before jumping directly to dlerror.
>>
>> I hope you guys can accept this change!
> 
> Yes, it'll be included but with an additional test that dlerror() returns 
> non-NULL. That should make the same code work on both platforms.
>