[Sbcl-devel] p-a and align-csp questions

[Cyrus H. <ch...@bo...>]

Dear sbcl-devel,

I have a couple, probably naive, questions regarding pseudo-alloc and  
align-csp on ppc:

1. What does the extra flag to pseudo-alloc do? I see that we  
subtract 4 from it and store it in flag-tn, but I'm not sure what the  
purpose of the extra argument is.

2. In align-csp, it appears that we're attempting to align a block of  
memory allocated on the stack to some multiple, but it's not clear to  
me what the alignment is. It looks like we check the alignment by  
anding with lowtag-mask (which is 7, but I don't understand why  
lowtag-mask should have anything to do with stack alignment) and if  
it's not zero we add n-word-bytes, or 4 in this case, to csp-tn. I'm  
sure there's some method to this madness, but I don't see it.

If anyone would be so kind as to help me figure out what's going on  
here, I would greatly appreciate it.

Thanks,

Cyrus