The perl binary has multiple ways in which it can be built. The simplest (and original) model just defines PL_stack_sp directly as a global variable. But when built with MULTIPLICITY (when for example building a threaded perl), then multiple interpreters are allowed, and (within the core), PL_stack_sp is defined as my_perl->Ispack_sp.

However in XS code (rather than in the core), it's more complex. At one point PL_stack_sp was defined as a function call, which would shield the XS code from changes in the interpreter struct layout across differing perl versions - so XS modules wouldn't have be to recompiled for each new perl release. However, this slowed XS code down a lot, and there were other things which also broke binary compatibility, so that was ditched and we just changed the binary guarantee to apply only across minor releases.

Dave.

In reply to Re^3: what definition of Istack_sp by dave_the_m
in thread what definition of Istack_sp by xiaoyafeng

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