[erlang-questions] Erlang on 64-bit ARM?

[Frank Hunleth]

On Sun, Jan 17, 2016 at 6:14 AM, Mikael Pettersson <mikpelinux@REDACTED> wrote:
> Frank Hunleth writes:
>  > I was wondering if anyone uses Erlang on a 64-bit ARM platform
>  > (aarch64)? The Buildroot project's CI servers are throwing linker
>  > errors such as the following:
>  >
>  >  LD /home/buildroot/autobuild/run/instance-0/output/build/erlang-17.5/bin/aarch64-buildroot-linux-gnu/child_setup
>  >  AR /home/buildroot/autobuild/run/instance-0/output/build/erlang-17.5/erts/emulator/pcre/obj/aarch64-buildroot-linux-gnu/opt/libepcre.a
>  >  LD /home/buildroot/autobuild/run/instance-0/output/build/erlang-17.5/bin/aarch64-buildroot-linux-gnu/beam
>  > ../lib/internal/aarch64-buildroot-linux-gnu/libethread.a(ethr_atomics.o):
>  > In function `AO_double_compare_and_swap':
>  > ethr_atomics.c:(.text+0x20): undefined reference to
>  > `__atomic_compare_exchange_16'
>  > ../lib/internal/aarch64-buildroot-linux-gnu/libethread.a(ethr_atomics.o):
>  > In function `AO_double_load':
>  > ethr_atomics.c:(.text+0x3c): undefined reference to `__atomic_load_16'
>  > ../lib/internal/aarch64-buildroot-linux-gnu/libethread.a(ethr_atomics.o):
>  > In function `ethr_dw_atomic_cmpxchg_acqb':
>  > ethr_atomics.c:(.text+0x5e8): undefined reference to `__atomic_load_16'
>  >
>  > See http://autobuild.buildroot.net/results/0cd/0cd22eb74fa29e5a85bf897762e16ab3daf33962/build-end.log
>  > for all of the error messages.
>  >
>  > I was able to reproduce the same errors on the 18.2.1 release as well.
>  > Possibly confounding the situation is that Buildroot crosscompiles
>  > Erlang. However, Erlang builds fine on all other platforms supported
>  > by Buildroot, and my attempt at reading the atomic intrinsics code was
>  > leading me down the path that aarch64 may not be supported. Could
>  > somewhere verify whether this is the case?
>
> OTP 18.2.1 builds fine using an aarch64-unknown-linux cross toolchain built
> using binutils-2.25.1, gcc-5.3.0, linux-3.19 kernel headers, and glibc-2.22,
> all unmodified upstream sources.
>
> However, if I also build and install libatomic_ops in that cross toolchain
> and add --with-libatomic_ops to OTP's ./configure, then I do get the same
> error as you cite above.
>
> Looks like some issue in OTP's interface to that library.  I've never looked
> into libatomics_ops myself, since I prefer to implement atomics by hand or by
> using gcc's builtins.
>
> Workaround for now is to not use libatomic_ops.  You may also want to file a
> bug in the bug tracker.

Thanks. I was able to build Erlang without libatomic_ops just like you
said. I've filed a bug, ERL-78, to track the issue.

Regards,
Frank