Re: [PATCH] -Warray-bounds TLC

[Marc Glisse <marc dot glisse at inria dot fr>]

On Fri, 17 Apr 2015, Steve Ellcey wrote:

> As a follow-up, I got the same error with dl-close.c from glibc and
> assumed it was the same type of code but when I looked at it and cut it
> down I got this code and error.  This seems more like a real GCC error
> (in that it should not be warning).  Note that I only get the error when
> bad is declared as 'noreturn'.
>
> Steve Ellcey
> sellcey@imgtec.com
>
>
>
> extern void bad (const char *__assertion)  __attribute__ ((__noreturn__));
> struct link_map { long int l_ns; };
> extern struct link_namespaces
>  {
>    unsigned int _ns_nloaded;
>  } _dl_ns[1];
> void _dl_close_worker (struct link_map *map)
> {
>  long int nsid = map->l_ns;
>  struct link_namespaces *ns = &_dl_ns[nsid];
>  (nsid != 0) ? (void) (0) : bad ("nsid != 0");
>  --ns->_ns_nloaded;
> }

It looks close enough to me. The actual access to _dl_ns[nsid] only ever 
happens for an index that is out of range. The last line of the function 
can never make sense (unreachable or undefined behavior), it is good that 
the compiler tells you about it.

--
Marc Glisse