Re: [boost] Help with a shared_ptr problem on Android (ARM)

Subject: Re: [boost] Help with a shared_ptr problem on Android (ARM)
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2014-04-17 09:32:28

On Thu, Apr 17, 2014 at 4:53 PM, Peter Dimov <lists_at_[hidden]> wrote:
> https://svn.boost.org/trac/boost/ticket/9912
>
> reports that spinlock_gcc_arm.hpp segfaults on a Nexus 7.
>
> Unfortunately, I know next to nothing about ARM or Android, so I wonder if
> someone can help with that.

I'm probably even less experienced with ARM than you are, but there is
an interesting comment in boost/atomic/detail/gcc-armv6plus.hpp that
explains some things about different ARM ISA versions.

>From Wikipedia it seems that Nexus 7 has an ARMv7 CPU, but the
compiler is probably reducing the target CPU to ARMv6 or even lower
(judging by the fact that __thumb__ is not defined). In this version
mcr instruction is used for a memory barrier. As I understand it, it's
basically an instruction for a co-processor (15 in this case). I
suspect that that particular SoC could have this co-processor number
reserved. Of course, all this is just a speculation on my part, so
take it with a grain of salt. It would be useful to see the backtrace
and disassembly to verify my theory.