FROM --platform=$BUILDPLATFORM alpine-$BUILDARCH uses TARGETARCH manifest #4237
Description
dockerfile:
# alpine-ARCH pattern is used in https://github.com/moby/buildkit/blob/v0.12.2/Dockerfile#L26-L33
FROM alpine:3.18 AS alpine-amd64
FROM alpine:3.18 AS alpine-arm64
FROM --platform=$BUILDPLATFORM alpine-$BUILDARCH
RUN set -x; [ "$(uname -m)" = "x86_64" ]
# Expected result (on amd64 hosts): "x86_64"
# Actual result: "aarch64"On amd64 hosts, buildctl build --opt platform=arm64 fails, as BuildKit unexpectedly uses TARGETARCH manifest.
A workaround is to use FROM --platform=$BUILDPLATFORM alpine:3.18 directly.