Subject: Re: Bug#827815: libmozjs-24-0: initialization
segfaults on sparc64



On 01/15/2017 04:57 PM, Simon McVittie wrote:
> This is easy to reproduce on the sparc64 porterbox, with or without gjs.
> Possibly related to <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=824449>
> since standalone mozjs (SpiderMonkey) is essentially a fork of the Firefox
> JavaScript engine.

The problem are tagged pointers which are used by many JavaScript
implementations
and are basically a crude hack only. They work as long as the underlying
hardware
does not use any beyond the 48 bit virtual address space which is currently
true for x86_64.

However, the arm64 have already run into this limit as well [1] and I expect
other
architectures to run into the problem at some point in the future as well. It's
just a bad design to make assumptions about the underlying hardware and violate
the C/C++ specification just to make the Javascript engine faster in some
benchmarks.

Some needs to fix the Javascript implementations at some point to get rid of
these
hacks and these issues will all be resolved.

For the time being, Firefox upstream is now using the arm64 workaround on
sparc64
as well which fixed Firefox on sparc64. Firefox will be fixed on sparc64 with
version 53.

Adrian

> [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1143022

--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer - [email protected]
`. `' Freie Universitaet Berlin - [email protected]
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