Under ithreads the optree is read only. If you want to enforce this, to
check for write accesses from buggy code, compile with
-C<-DPL_OP_SLAB_ALLOC> to enable the old OP slab allocator and
C<-DPERL_DEBUG_READONLY_OPS> to enable code that allocates op memory
-via C<mmap>, and sets it read-only at run time. (PERL_DEBUG_READONLY_OPS
-has not been rewritten for the new slab allocator, so op trees may leak.)
-Any write access to an op results in a C<SIGBUS> and abort.
+via C<mmap>, and sets it read-only when it is attached to a subroutine. Any
+write access to an op results in a C<SIGBUS> and abort.
This code is intended for development only, and may not be portable
even to all Unix variants. Also, it is an 80% solution, in that it
-isn't able to make all ops read only. Specifically it
+isn't able to make all ops read only. Specifically it does not apply to op
+slabs belonging to C<BEGIN> blocks.
-=over
-
-=item * 1
-
-Only sets read-only on all slabs of ops at C<CHECK> time, hence ops
-allocated later via C<require> or C<eval> will be re-write
-
-=item * 2
-
-Turns an entire slab of ops read-write if the refcount of any op in the
-slab needs to be decreased.
-
-=item * 3
-
-Turns an entire slab of ops read-write if any op from the slab is
-freed.
-
-=back
-
-It's not possible to turn the slabs to read-only after an action
-requiring read-write access, as either can happen during op tree
-building time, so there may still be legitimate write access.
-
-However, as an 80% solution it is still effective, as currently it
-catches a write access during the generation of F<Config.pm>, which
-means that we can't yet build F<perl> with this enabled.
+However, as an 80% solution it is still effective, as it has caught bugs in
+the past.
=head2 The .i Targets
https://perl5.git.perl.org / perl5.git / blobdiff