Handle trampolines correctly in new FCC API + usages

[Girgias]

So I finally understand what php-src calls trampolines, and they are extremely annoying to deal with.

I've taken the code to handle them from the SPL class autoloading mechanism, however I haven't yet figured out why SPL copies the function handler when fcc->function_handler == &EG(trampoline).

This makes me wonder if this is the reason why no FCC API was introduced previously as you would need to carry the zval callable around which would would recreate the trampoline each time.

Moreover, the refetching of the trampoline which is freed by ZPP should probably be part of some explicit API that we provide if in the end we thing providing an FCC API is sensible.

[arnaud-lb]

I haven't yet figured out why SPL copies the function handler when fcc->function_handler == &EG(trampoline)

My understanding is that EG(trampoline) is an allocation cache slot to store a trampoline. It is used to avoid an allocation in zend_get_call_trampoline_func. The slot is considered to be free to use when EG(trampoline).common.function_name == NULL.

SPL copies EG(trampoline) and resets EG(trampoline).common.function_name to make the slot available again to future zend_get_call_trampoline_func calls.

[Girgias]

I haven't yet figured out why SPL copies the function handler when fcc->function_handler == &EG(trampoline)

My understanding is that EG(trampoline) is an allocation cache slot to store a trampoline. It is used to avoid an allocation in zend_get_call_trampoline_func. The slot is considered to be free to use when EG(trampoline).common.function_name == NULL.

SPL copies EG(trampoline) and resets EG(trampoline).common.function_name to make the slot available again to future zend_get_call_trampoline_func calls.

Ah, so I suppose it's a wise idea to free this when doing the copy. :)

[arnaud-lb]

This is redundant with the fcc->function_handler->common.function_name = NULL above.

It may be enough to just set EG(trampoline).common.function_name to NULL (this is what zend_free_trampoline does, and EG(trampoline).common.function_name only looks at EG(trampoline).common.function_name to check that the slot is free).