Re: Clarification on newlib version for building AMDGCN offloading backend

[Wileam Yonatan Phan <wileamyp@outlook.com>]

Hi Andrew,

Just wanna follow up on the progress of this endeavor of enabling GCC with AMDGCN offloading in Spack. So far I think I've got everything working, except for the part where libgomp is pulled from the wrong place at runtime, because Spack prefers using RPATH to LD_LIBRARY_PATH. As outlined in the Spack PR comments, the proposed fix is modifying the *link_gomp field inside <install-prefix>/lib/gcc/amdgcn-amdhsa/<gcc-version>/specs to add the rpath flags for libgomp. But I'm honestly unsure if this should be done at configure time, build time, or install time.

The Spack PR can be accessed here: <https://github.com/spack/spack/pull/35919>

Please advise,
Wil

From: Andrew Stubbs <ams@codesourcery.com>
Sent: Thursday, March 30, 2023 04:45
To: Wileam Yonatan Phan <wileamyp@outlook.com>; gcc@gcc.gnu.org <gcc@gcc.gnu.org>
Subject: Re: Clarification on newlib version for building AMDGCN offloading backend 
 
On 29/03/2023 19:18, Wileam Yonatan Phan wrote:
> Hi Andrew,
> 
> I just built GCC 12.2.0 with AMDGCN offloading successfully with Spack!
> However, when I tried to test it with an OpenACC test code that I have, I encountered the following error message:
> 
> wyp@basecamp:~/work/testcodes/f90-acc-ddot$ gfortran -fopenacc -foffload=amdgcn-unknown-amdhsa="-march=gfx900" ddot.f90
> as: unrecognized option '-triple=amdgcn--amdhsa'
> mkoffload: fatal error: x86_64-pc-linux-gnu-accel-amdgcn-unknown-amdhsa-gcc returned 1 exit status
> compilation terminated.
> lto-wrapper: fatal error: /home/wyp/work/spack/opt/spack/linux-ubuntu20.04-zen2/gcc-12.2.0/gcc-12.2.0-w7lclfarefmge3uegn2a5vw37bnwhwto/libexec/gcc/x86_64-pc-linux-gnu/12.2.0//accel/amdgcn-unknown-amdhsa/mkoffload returned 1 exit status
> compilation terminated.
> /usr/bin/ld: error: lto-wrapper failed
> collect2: error: ld returned 1 exit status

My guess is that it's trying to use the wrong assembler. Usually this 
means there is a problem with your installation procedure and/or your 
PATH. I think you should be able to investigate further using -v and/or 
strace. The correct one should be named 
$DESTDIR/usr/local/amdgcn-amdhsa/bin/as, but this will be different if 
you configured GCC with a custom --prefix location. If you have 
relocated the toolchain since installation then the toolchain will 
attempt to locate libraries and tools relative to the gcc binary. If it 
does not find them there then it looks in the "usual places", and those 
usually contain an "as" suitable only for the host system.

If you find an error on the Wiki instructions please let me know and I 
will correct them.

Andrew