Re: [PATCH] Come up with --param asan-stack-small-redzone (PR sanitizer/81715).

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Sep 25, 2018 at 11:05:30AM +0200, Martin Liška wrote:
> As requested in PR81715, GCC emits bigger middle redzones for small variables.
> It's analyzed in following comment: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715#c28

First of all, does LLVM make the variable sized red zone size only for
automatic variables, or also for global/local statics, or for alloca?

Have you considered also making the red zones larger for very large
variables?

> For now I'm suggesting to shrink shadow memory for variables <= 16B to 32B (including variable storage).
> LLVM is more aggressive as they allocate just 16B of shadow memory for variables <= 4B. That would
> require bigger code refactoring in asan.c and I would like to avoid that.

What exactly would need changing to support the 12-15 bytes long red zones
for 4-1 bytes long automatic vars?
Just asan_emit_stack_protection or something other?

> +	      poly_uint64 size = stack_vars[i].size;
> +	      /* For small variables shrink middle redzone (including
> +	       * variable store) just to ASAN_RED_ZONE_SIZE.  */

We don't use this comment style (* at start of comment continuation lines).
Otherwise it looks reasonable, but I wouldn't stop here.

	Jakub