question about "-fstack-protector" and fedora

[Jakub Jelinek]

On Thu, Jun 30, 2011 at 03:31:24PM +0200, Jakub Jelinek wrote:
> On Thu, Jun 30, 2011 at 03:19:10PM +0200, Reindl Harald wrote:
> > as far as i can see fedora is built with "-fstack-protector" and not
> > "-fstack-protector-all" - is there a specific reason for not using
> > the "all" variant
> 
> Sure, it is expensive to set up the canary even when it is obvious
> it isn't needed.  We by default use 4 byte+ arrays as the trigger to
> add stack canaries (gcc default is 8 byte+), with -fstack-protector-all
> you add it even for functions that don't have any stack variables at
> all, or that have only scalar vars etc.

I'd add that even functions as simple as
int foo (void) { return 1; }
are "protected" with -fstack-protector-all, with -fstack-protector
this function has 2 instructions, with -fstack-protector-all 11, which
includes creating a stack frame etc.
Really, -fstack-protector --param=ssp-buffer-size=4 is carefully chosen
reasonable default, just don't listen to clueless LFS/Gentoo folks
that suggest something else.

	Jakub