Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: 741a5c7396a0ca90a22ea8d8e0761c70c14b0a77
      
https://github.com/Perl/perl5/commit/741a5c7396a0ca90a22ea8d8e0761c70c14b0a77
  Author: Yves Orton <demer...@gmail.com>
  Date:   2022-09-02 (Fri, 02 Sep 2022)

  Changed paths:
    M INSTALL
    M embedvar.h
    M intrpvar.h
    M op.c
    M perl.h
    M pod/perldelta.pod
    M pod/perldiag.pod
    M pod/perlfunc.pod
    M pod/perlvar.pod
    M sv.c
    M t/op/eval.t

  Log Message:
  -----------
  op.c - Restrict nested eval/BEGIN blocks to a user controllable maximum

Nested BEGIN blocks can cause us to segfault by exhausting
the C stack. Eg:

    perl -le'sub f { eval "BEGIN { f() }" } f()'

will segfault. This adds a new interpreter var PL_eval_begin_nest_depth
to keep track of how many layer of eval/BEGIN we have seen, and a new
reserved variable called ${^MAX_NESTED_EVAL_BEGIN_BLOCKS} which can be
used to raise or lower the limit. When set to 0 it blocks BEGIN entirely,
which might be useful from time to time.

This fixes https://github.com/Perl/perl5/issues/20176


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