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Re: Ruby testsuite failures because of pointer mangling on 32-bit ARM?

On 12/12/2013 09:53 PM, Rich Felker wrote:
> On Thu, Dec 12, 2013 at 01:20:53PM -0500, David Miller wrote:
>> From: David Miller <>
>> Date: Thu, 12 Dec 2013 12:14:41 -0500 (EST)
>>> From: "Carlos O'Donell" <>
>>> Date: Thu, 12 Dec 2013 00:55:01 -0500
>>>> It treats the jmp_buf as an array of VALUE sized pointers that
>>>> it can examine to determine if there are pointers to the heap.
>>> Sounds similar to what any other garbage collector will do, scan
>>> the processes address space looking for pointers.
>>> I'm pretty sure Boehm-GC does something similar, although perhaps
>>> it scans the entire process stack from the point in which it is
>>> called instead of using jmpbuf's to delineate spans of stack
>>> areas like Ruby does.
>> And, indirectly, realize that even a straight stack scan is going
>> to potentially break if you start mangling pointers in jmpbuf.
>> Consider the case where if the jmpbuf is on the processes stack, and
>> normally it would get scanned by GC and the pointer followed to find
>> memory references, and now that would not work because the pointer is
>> mangled.
>> I think all of these schemes are legitimate and erroneously broken
>> by pointer mangling.
> Applying garbage collection to C objects is about as far away from
> "legitimate" as you can possibly get.
> Rich

This now bug #9249 in the ruby bug tracker.

I hope we can discuss alternatives to the current implementation
and come up with something we can all agree on.

The strongest argument to make is to consider that ruby *is* part
of the "implementation" and therefore privy to the contents of
jmp_buf. If glibc agrees to that then we would need to document
this hard requirement and work out some way to coordinate jmp_buf
changes with ruby.


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