Setting a default value for OPT_INIT_ALL (stable=zero, current=pattern)

Hi,

we have support to set a default initialization value for uninitialized 
variables (OPT_INIT_ALL in src.conf). Possible values are (copy&paste 
from 
https://gcc.gnu.org/pipermail/gcc-patches/2021-February/565514.html):
'-ftrivial-auto-var-init=CHOICE'
      Initialize automatic variables with either a pattern or with zeroes
      to increase program security by preventing uninitialized memory
      disclosure and use.

      The three values of CHOICE are:

         * 'uninitialized' doesn't initialize any automatic variables.
           This is C and C++'s default.

         * 'pattern' Initialize automatic variables with values which
           will likely transform logic bugs into crashes down the line,
           are easily recognized in a crash dump and without being values
           that programmers can rely on for useful program semantics.
           The values used for pattern initialization might be changed in
           the future.

         * 'zero' Initialize automatic variables with zeroes.

      The default is 'uninitialized'.

The main point of this option is to prevent leaking random data by 
accident.

What I propose is to have OPT_INIT_ALL set to "zero" in stable branches. 
We could maybe also set it to "pattern" in -current. In my opinion this 
a similar thing like the malloc production setting, or witness, and so 
on.

Any thoughts about this?

In case of a generic consensus of this, I would expect the release 
engineering team to take this into their procedure for branching a new 
stable branch. The locations where a OPT_INIT_ALL?=zero would need to be 
added are share/mk/bsd.lib.mk, share/mk/bsd.prog.mk and 
sys/conf/kern.mk.

Bye,
Alexander.

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