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

[Dan Sugalski]

At 3:27 PM +0100 10/29/02, Leopold Toetsch wrote:

Jason Gloudon wrote:

On Tue, Oct 29, 2002 at 02:40:14PM +0100, Leopold Toetsch wrote:

+ cur_var_ptr = (size_t)((ptrdiff_t)cur_var_ptr + PARROT_PTR_ALIGNMENT)

When PARROT_PTR_ALIGNMENT is not 1, that much pointers -1 are skipped during stack scanning by incrementing cur_var_ptr by sizeof(size_t) * PARROT_PTR_ALIGNMENT bytes.

ptrdiff_t is not a pointer type, so cur_var_ptr + PARROT_PTR_ALIGNMENT skips
exactly PARROT_PTR_ALIGNMENT bytes. You may not be matching ( )'s quite right.

Brr, yes. I checked with gdb. cur_var_ptr is incremented by PARROT_PTR_ALIGNMENT _bytes_ i.e. by 1 byte on i386. Can we really have e.g. odd aligned PMCs on stack? I don't think so. Or am I still missing something?

There was some indication back when this was first implemented that the i386, at least when running windows, could have odd-aligned pointers in stack-allocated data. Nobody was 100% sure, but better safe than not, at least until someone can say definitively that we're being too cautious.
--
Dan

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