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

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux