Re: [PATCH] Do without union of variable length arrays.

[Alexander Cherepanov <ch3root at openwall dot com>]

On 2015-09-16 18:25, Mark Wielaard wrote:
> On Fri, 2015-09-11 at 12:22 -0700, Roland McGrath wrote:
>> It looks fine to me from a quick skim, but Mark should review and test it too.
>
> I am not super enthusiastic about this change, it seems to just take
> away type/size information that the compiler/bounds checking tools can
> use.

I'm not sure I fully understand the problem. As I understand it unions 
of VLAs are not Ok while VLAs are Ok and even desirable due to bounds 
checking, right?

Why not just use VLAs of unions? Cold memory?

Given that the current approach (before the patch) already required to 
write superfluous "->" perhaps an approach requiring a superfluous "*" 
will fit? Like this:

   void *data = malloc (...);
   T32 (*a32)[n] = data;
   T64 (*a64)[n] = data;

Then the use looks like "(*a32)[i].member". Clang seems to be happy and 
its UBSAN works fine.

-- 
Alexander Cherepanov