Re: Not a GCC bug (was Re: Big GCC bug!!! [Was: Re: Do not misuse Coverity please])

[Nick Piggin <nickpiggin@yahoo.com.au>]

Kyle Moffett wrote:
> On Mar 30, 2005, at 18:38, Jakub Jelinek wrote:
> 
>> This testcase violates ISO C99 6.3.2.3:
>> If a null pointer constant is converted to a pointer type, the resulting
>> pointer, called a null pointer, is guaranteed to compare unequal to a
>> pointer to any object or function.
> 
> 
> Except that the result of dereferencing a null pointer is implementation
> defined according to the C99 standard.  My implementation allows me to mmap
> stuff at NULL, and therefore its compiler should be able to handle that
> case.  I would have no problem with either the standard or implementation
> if it either properly handled the case or didn't allow it in the first
> place.
> 
> On another note, I've discovered the flag 
> "-fno-delete-null-pointer-checks",
> which should probably be included in the kernel makefiles to disable that
> optimization for the kernel.  (Ok, yes, I apologize, this isn't really a 
> GCC
> bug, the behavior is documented, although it can be quite confusing.  I
> suspect it may bite some platform-specific code someday.  It also muddies
> the waters somewhat with respect to the original note (and the effects on
> the generated code):
> 
>> int x = my_struct->the_x;
>> if (!my_struct) return;
> 

Why should this be in the kernel makefiles? If my_struct is NULL,
then the kernel will never reach the if statement.

A warning might be nice though.