DPDK patches and discussions
 help / color / mirror / Atom feed
From: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>
To: dev@dpdk.org, Ferruh Yigit <ferruh.yigit@intel.com>,
	Bruce Richardson <bruce.richardson@intel.com>,
	Leyi Rong <leyi.rong@intel.com>
Cc: David Marchand <david.marchand@redhat.com>,
	Akhil Goyal <gakhil@marvell.com>
Subject: buildtools/binutils-avx512-check.sh
Date: Fri, 12 Nov 2021 16:08:37 +0300	[thread overview]
Message-ID: <20211112160837.131994aa@sovereign> (raw)

Hello,

I'm working on improvement of Linux-to-Windows cross-compilation using MinGW.
Currently there is c_args = '-mno-avx512f' in config/x86/cross-mingw, however,
1) baseline meson 0.49.2 doesn't like it*
2) it should be in machine_args because they are checked in various places
3) I don't like disabling AVX512F if there is really no issue**
So I started looking at the subject script.

* '-mno-avx512f' should be ['-mno-avx512f'], but then the build of lib/net
  breaks, because meson 0.49.2 and 0.57.0 (native Windows baseline)
  order compiler arguments differently.

** There was a .seh_savemm bug with MinGW that -mno-avx512f was trying to fix,
   but I believe that -fno-asynchronous-unwind tables was the final solution.
   However, AVX512 support is still broken for native MinGW builds, see below.

First question. In config/x86/meson.build we have:

# get binutils version for the workaround of Bug 97
if not is_windows
    binutils_ok = run_command(binutils_avx512_check)
    if binutils_ok.returncode() != 0 and cc.has_argument('-mno-avx512f')
        machine_args += '-mno-avx512f'
        warning('Binutils error with AVX512 assembly, disabling AVX512
support')
    endif
endif

This is a GNU binutils bug and if I understand correctly,
it doesn't affect builds that use LLVM binutils (FreeBSD and Windows+clang).
The script also uses ${AS:-as} and objdump, that may be missing.
Consequently, AVX512F may be disabled for LLVM-based builds
because GNU toolchain has a bug or is just absent:

root@freebsd:/tmp/dpdk # meson build
[...]
config/x86/meson.build:9: WARNING: Binutils error with AVX512 assembly,
disabling AVX512 support
[...]

root@freebsd:/tmp/dpdk # uname -r
13.0-RELEASE

root@freebsd:/tmp/dpdk # ./buildtools/binutils-avx512-check.sh
./buildtools/binutils-avx512-check.sh: as: not found
./buildtools/binutils-avx512-check.sh: objdump: not found
vpgatherqq displacement error with as

Probably the script output and its check should be enhanced
to distinguish between its failure and success with negative answer?
Or should the check be done under a condition like this?

	if not is_windows and (is_linux or cc.get_id() == 'gcc')


The next question is the preferred approach to fix things for Windows.
Current status:
1) MinGW 8.1.0 on Windows: buggy
2) MinGW 7.0.0 on Linux: OK
3) LLVM on Windows: OK

One solution is simply state this:

	if not is_windows
		binutils_bug_97 = ... # run the script
	elif cc.get_id() == 'gcc'
		binutils_bug_97 = true
	endif
	if binutils_bug_97
		machine_args += '-mno-avx512f'
		warning('...')
	endif

Another one is to make the script portable
and run it when LLVM is not used, on any OS, including cross builds.
By the way, $AS and objdump binaries may be overridden in a --cross-file,
so in this case we should locate them with meson.
What to others think?

             reply	other threads:[~2021-11-12 13:08 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-12 13:08 Dmitry Kozlyuk [this message]
2021-11-12 13:43 ` buildtools/binutils-avx512-check.sh Bruce Richardson

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20211112160837.131994aa@sovereign \
    --to=dmitry.kozliuk@gmail.com \
    --cc=bruce.richardson@intel.com \
    --cc=david.marchand@redhat.com \
    --cc=dev@dpdk.org \
    --cc=ferruh.yigit@intel.com \
    --cc=gakhil@marvell.com \
    --cc=leyi.rong@intel.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).