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Re: Ruby testsuite failures because of pointer mangling on 32-bit ARM?
- From: Rich Felker <dalias at aerifal dot cx>
- To: David Miller <davem at davemloft dot net>
- Cc: carlos at redhat dot com, pinskia at gmail dot com, will dot newton at linaro dot org, libc-alpha at sourceware dot org
- Date: Thu, 12 Dec 2013 21:53:24 -0500
- Subject: Re: Ruby testsuite failures because of pointer mangling on 32-bit ARM?
- Authentication-results: sourceware.org; auth=none
- References: <20131210 dot 211901 dot 1840879367475720601 dot davem at davemloft dot net> <52A94FB5 dot 7060100 at redhat dot com> <20131212 dot 121441 dot 261870704107659875 dot davem at davemloft dot net> <20131212 dot 132053 dot 446942135510037848 dot davem at davemloft dot net>
On Thu, Dec 12, 2013 at 01:20:53PM -0500, David Miller wrote:
> From: David Miller <firstname.lastname@example.org>
> Date: Thu, 12 Dec 2013 12:14:41 -0500 (EST)
> > From: "Carlos O'Donell" <email@example.com>
> > 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
> 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.