Why Do ARMv8 and ARMv9 Images Both Appear Only as arm64?

Description

System Information

Gracehopper

~$ lscpu
Architecture:             aarch64
  CPU op-mode(s):         64-bit
  Byte Order:             Little Endian
CPU(s):                   72
  On-line CPU(s) list:    0-71
Vendor ID:                ARM
  Model name:             Neoverse-V2


~$ hostnamectl
Operating System: Ubuntu 22.04.5 LTS                  
          Kernel: Linux 6.8.0-1025-nvidia-64k
    Architecture: arm64
 Hardware Vendor: Supermicro
  Hardware Model: ARS-111GL-NHR

~$ docker --version
Docker version 28.0.4, build b8034c0

~$ which docker
/usr/bin/docker

$ snap list docker
error: no matching snaps installed

Jetson

~$ hostnamectl
Operating System: Ubuntu 22.04.5 LTS                  
          Kernel: Linux 5.15.136-tegra
    Architecture: arm64
 Hardware Vendor: NVIDIA
  Hardware Model: NVIDIA Jetson AGX Orin Developer Kit

~$ lscpu
Architecture:            aarch64
  CPU op-mode(s):        32-bit, 64-bit
  Byte Order:            Little Endian
CPU(s):                  12
  On-line CPU(s) list:   0-11
Vendor ID:               ARM
  Model name:            Cortex-A78AE

~$ docker --version
Docker version 28.4.0, build d8eb465

~$ which docker
/usr/bin/docker

~$ snap list docker
error: no matching snaps installed

Building Images

Jetson

$ docker build -t my-alpine-app .
$ docker tag my-alpine-app dockerhubuser/test-alpine:jetsonV8
$ docker push dockerhubuser/test-alpine:jetsonV8

Gracehopper

$ docker build -t my-alpine-app .
$ docker tag my-alpine-app dockerhubuser/test-alpine:gracehopperNeoverseV2
$ docker push dockerhubuser/test-alpine:gracehopperNeoverseV2

Both images were built from the same simple Dockerfile shown below:

$ cat Dockerfile 
FROM alpine:3.18
WORKDIR /app
COPY . /app

DockerHub

On Docker Hub, both images appear simply as linux/arm64, without specifying a variant.
But when I check official images such as Alpine, the variant is shown as v8.

• Since Gracehopper uses ARMv9 (Neoverse V2), why isn’t the variant reflected (e.g., v9)?
• Is v8 currently considered the default for arm64, and v9 not yet officially recognized by Docker Hub/OCI specs?
• Is there a way to explicitly set or detect the v9 variant when building and pushing images?

Multi-Architecture Build

I also experimented with a multi-architecture build targeting three platforms: amd64, Gracehopper (ARMv9), and Jetson (ARMv8).

System Information for x86-64

~$ hostnamectl
Operating System: Ubuntu 24.04.1 LTS              
          Kernel: Linux 6.8.0-60-generic
    Architecture: x86-64
 Hardware Vendor: Dell Inc.

~$ lscpu
Architecture:             x86_64
  CPU op-mode(s):         32-bit, 64-bit
  Address sizes:          43 bits physical, 48 bits virtual
  Byte Order:             Little Endian
CPU(s):                   64
  On-line CPU(s) list:    0-63
Vendor ID:                AuthenticAMD
  Model name:             AMD EPYC 7282 16-Core Processor

~$ docker --version
Docker version 28.1.1, build 4eba377

~$ which docker
/usr/bin/docker

~$ docker buildx version
github.com/docker/buildx v0.23.0 28c90ea

Building Images

docker buildx build   --target oai-lmf   --tag dockerhubuser/oai-lmf:gh-jetson   --platform linux/amd64,linux/arm64/v8,linux/arm64   --file docker/Dockerfile.lmf.ubuntu   --builder gh-jetson-multiarchbuilder   --progress=plain   --push . 2>&1 | tee LMF_log_multiarch_buildx.log

When explicitly specifying platforms like this:

--platform linux/amd64,linux/arm64/v8,linux/arm64/v9

the build ran for about 45 minutes (roughly 3× longer than the same Dockerfile on a single architecture) before failing.

If I instead use:

--platform linux/amd64,linux/arm64/v8,linux/arm64

Even though this warning appears, the build still completes and the image is pushed to Docker Hub — but without any variant being shown (only linux/arm64).

1 warning found (use docker --debug to expand):
 - Duplicate platform result requested "linux/arm64"

Reproduce

$ cat Dockerfile 
FROM alpine:3.18
WORKDIR /app
COPY . /app

Build the above image, from both Jetson and Gracehopper; and push to dockerhub

$ docker build -t my-alpine-app .
$ docker tag my-alpine-app dockerhubuser/test-alpine:jetsonV8
$ docker push dockerhubuser/test-alpine:jetsonV8

$ docker build -t my-alpine-app .
$ docker tag my-alpine-app dockerhubuser/test-alpine:gracehopperNeoverseV2
$ docker push dockerhubuser/test-alpine:gracehopperNeoverseV2

Expected behavior

Docker is treating image build on Gracehopper ARM Neoverse v9 as only arm64 and not with the variant

docker version

Gracehopper:


~$ docker version
Client: Docker Engine - Community
 Version:           28.0.4
 API version:       1.48
 Go version:        go1.23.7
 Git commit:        b8034c0
 Built:             Tue Mar 25 15:07:33 2025
 OS/Arch:           linux/arm64
 Context:           default


Jetson


~$ docker version
Client: Docker Engine - Community
 Version:           28.4.0
 API version:       1.51
 Go version:        go1.24.7
 Git commit:        d8eb465
 Built:             Wed Sep  3 20:58:58 2025
 OS/Arch:           linux/arm64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          28.4.0
  API version:      1.51 (minimum version 1.24)
  Go version:       go1.24.7
  Git commit:       249d679
  Built:            Wed Sep  3 20:58:58 2025
  OS/Arch:          linux/arm64
  Experimental:     false
 containerd:
  Version:          1.7.27
  GitCommit:        05044ec0a9a75232cad458027ca83437aae3f4da
 runc:
  Version:          1.2.5
  GitCommit:        v1.2.5-0-g59923ef
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

docker info

Gracehopper


$ docker info
Client: Docker Engine - Community
 Version:    28.0.4
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.22.0
    Path:     /usr/libexec/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.34.0
    Path:     /usr/libexec/docker/cli-plugins/docker-compose

Server:
 Containers: 2
  Running: 2
  Paused: 0
  Stopped: 0
 Images: 35
 Server Version: 28.0.4
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: systemd
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog
 Swarm: inactive
 Runtimes: runc io.containerd.runc.v2 nvidia
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 753481ec61c7c8955a23d6ff7bc8e4daed455734
 runc version: v1.2.5-0-g59923ef
 init version: de40ad0
 Security Options:
  apparmor
  seccomp
   Profile: builtin
  cgroupns
 Kernel Version: 6.8.0-1025-nvidia-64k
 Operating System: Ubuntu 22.04.5 LTS
 OSType: linux
 Architecture: aarch64
 CPUs: 72
 Total Memory: 478.5GiB


Jetson:


~$ docker info
Client: Docker Engine - Community
 Version:    28.4.0
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.27.0
    Path:     /usr/libexec/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.39.2
    Path:     /usr/libexec/docker/cli-plugins/docker-compose

Server:
 Containers: 1
  Running: 1
  Paused: 0
  Stopped: 0
 Images: 13
 Server Version: 28.4.0
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: systemd
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog
 CDI spec directories:
  /etc/cdi
  /var/run/cdi
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 nvidia runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 05044ec0a9a75232cad458027ca83437aae3f4da
 runc version: v1.2.5-0-g59923ef
 init version: de40ad0
 Security Options:
  seccomp
   Profile: builtin
  cgroupns
 Kernel Version: 5.15.136-tegra
 Operating System: Ubuntu 22.04.5 LTS
 OSType: linux
 Architecture: aarch64
 CPUs: 12
 Total Memory: 61.37GiB

Additional Info

No response

No source file or test is named. Start by reproducing the shown docker build and buildx build commands with linux/arm64, linux/arm64/v8, and linux/arm64/v9, then inspect the pushed manifest metadata and the duplicate-platform warning. Done means the ARM variant behavior is explained or a confirmed, scoped fix is identified.