Re: [perl #18127] [PATCH] Implicit stack direction probe

[Dan Sugalski]

At 9:41 AM +0100 10/30/02, Leopold Toetsch wrote:

Jason Gloudon wrote:

... By default both compilers align stack variables at their natural
alignment, so PMC pointers would normally fall on 4 byte boundaries.

However, it is also possible that someone might save a PMC pointer to an
unaligned address on the stack (I can't imagine why). We could always say
"don't do that!" for performance reasons.

So, this "someone" are we (parrot itself) + language extensions (PXS) which have to be compiled with the same compiler options, parrot is compiled with.
Using packed structures with PMCs/Buffers inside is a strict "don't do that!".

I'm comfortable with this. If extensions use stack-allocated structs that have misaligned PMC/Buffer pointers in them, then the extension authors can darned well explicitly register the pointers for their lifetime. Except in rare and bizarre cases, it would have to be done explicitly--it's not like too many system structs are going to have pointers to our stuff in them.

Definitely warrants a big warning in the extension docs, but that's fine. Also warrants some seriously heavy-duty tests in the test suite to make sure we don't trip over compiler bugs or other strange things that would bite us because of this.
--
Dan

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