From: Sylvain Joyeux <sylvain.joyeux@...4x.org>
Date: 2009-01-07T18:19:10+09:00
Subject: [ruby-core:21188] Re: [PATCH] Update to MBARI patches on	1.8.7-p72

On Wed, Jan 07, 2009 at 04:35:18PM +0900, Brent Roman wrote:
> 
> Sylvain,
> 
> Man, the PowerPC is a weird beast.
> 
> After spending a couple hours looking over its ABI docs, I've convinced
> myself that the stack pointer would be valid for stack clearing if one could
> get to at it directly from the C code.  MBARI7 introduced a bit of gcc asm
> to do this for x86.  I've posted an update to the MBARI7 patch on my website
> that adds asm cases to get the stack pointer for PPC and ARM processors.  I
> don't have ready access to a PowerPC machine, so I'll have to rely on others
> to test this.
> 
> Oddly enough, there has long been (and still is) code in gc.c that gets the
> stack pointer via alloc(0), but it does not crash on PPC because that
> pointer is only used to determine the approximate stack depth for catching
> infinite recursion in Ruby scripts.
You should read commit messages when someone points you to one ;-)
That's basically what I said in the message, except that I thought it
was also used to delimit the stack in the mark phase.

Anyway, it works because
 * the stack is not modified
 * there is no ruby variables that can be stored in-between the alloca()
   space and the stack pointer which is not already somewhere else (in
   registers, and the register window is also dumped by the GC AFAIK).

> P.S.  I'll be trying to learn git and github over the coming weeks.  Perhaps
> we can keep these patches and yours in one place eventually.

Well, it will be as simple as cloning my repository in one common place.
I already updated my patch to work on top of MBARI7 with ASM as well ...
We'll see what to keep I guess.

My updated patch is here:
  http://github.com/doudou/ruby/commit/f02bea5b10fea4dfd5157002fdfc04b03ed26185

Sylvain