Add concept of native Dockerfile.

docker/Dockerfile.native

@@ -0,0 +1,27 @@
+FROM ubuntu:20.04
+ARG DEBIAN_FRONTEND=noninteractive
+
+COPY common.sh lib.sh /
+RUN /common.sh
+
+COPY cmake.sh /
+RUN /cmake.sh
+
+COPY xargo.sh /
+RUN /xargo.sh
+
+ARG TARGET_ARCH
+ARG QEMU_ARCH=$TARGET_ARCH
+
+COPY qemu.sh /
+RUN /qemu.sh $QEMU_ARCH softmmu
+
+COPY dropbear.sh /
+RUN /dropbear.sh
+
+COPY linux-image.sh /
+RUN /linux-image.sh $TARGET_ARCH
+
+COPY linux-runner /
+
+ENV CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUNNER="/linux-runner $TARGET_ARCH"

xtask/Cargo.toml

@@ -1,4 +1,5 @@
 [package]
+build = "src/build.rs"
 documentation = "https://github.com/cross-rs/cross"
 license = "MIT OR Apache-2.0"
 name = "xtask"

xtask/src/build.rs

@@ -0,0 +1,6 @@
+fn main() {
+    println!(
+        "cargo:rustc-cfg=cross_triple=\"{}\"",
+        std::env::var("TARGET").expect("rustc must set the TARGET environment variable")
+    );
+}

xtask/src/build_docker_image.rs

@@ -3,6 +3,7 @@ use std::path::Path;
 
 use crate::util::{cargo_metadata, gha_error, gha_output, gha_print};
 use clap::Args;
+use cross::docker::Architecture;
 use cross::docker::ImagePlatform;
 use cross::shell::MessageInfo;
 use cross::{docker, CommandExt, ToUtf8};
@@ -165,6 +166,7 @@ pub fn build_docker_image(
         platform
     };
 
+    let native_dockerfile = docker_root.join("Dockerfile.native").to_utf8()?.to_string();
     let mut results = vec![];
     for (platform, (target, dockerfile)) in targets
         .iter()
@@ -179,7 +181,66 @@ pub fn build_docker_image(
         docker_build.args(&["buildx", "build"]);
         docker_build.current_dir(&docker_root);
 
-        docker_build.args(&["--platform", &platform.docker_platform()]);
+        // add our platform, and determine if we need to use a native docker image
+        let docker_platform = platform.docker_platform();
+        let mut dockerfile = dockerfile.clone();
+        docker_build.args(&["--platform", &docker_platform]);
+        if target.sub.is_none() {
+            match (
+                engine.arch.as_ref(),
+                docker_platform.as_str(),
+                target.name.as_str(),
+            ) {
+                (Some(Architecture::I386), "linux/386", "i686-unknown-linux-gnu") => {
+                    dockerfile = native_dockerfile.clone();
+                    docker_build.args(&["--build-arg", "TARGET_ARCH=i686"]);
+                    docker_build.args(&["--build-arg", "QEMU_ARCH=i386"]);
+                }
+                (Some(Architecture::Amd64), "linux/amd64", "x86_64-unknown-linux-gnu") => {
+                    dockerfile = native_dockerfile.clone();
+                    docker_build.args(&["--build-arg", "TARGET_ARCH=x86_64"]);
+                }
+                (Some(Architecture::Arm), "linux/arm/v6", "arm-unknown-linux-gnueabi")
+                    if is_armv6() =>
+                {
+                    note_host_target_detection(msg_info)?;
+                    dockerfile = native_dockerfile.clone();
+                    docker_build.args(&["--build-arg", "TARGET_ARCH=arm"]);
+                }
+                (
+                    Some(Architecture::Arm),
+                    "linux/arm" | "linux/arm/v7",
+                    "armv7-unknown-linux-gnueabihf",
+                ) if is_armv7() => {
+                    note_host_target_detection(msg_info)?;
+                    dockerfile = native_dockerfile.clone();
+                    docker_build.args(&["--build-arg", "TARGET_ARCH=armv7"]);
+                    docker_build.args(&["--build-arg", "QEMU_ARCH=arm"]);
+                }
+                (
+                    Some(Architecture::Arm64),
+                    "linux/arm64" | "linux/arm64/v8",
+                    "aarch64-unknown-linux-gnu",
+                ) => {
+                    dockerfile = native_dockerfile.clone();
+                    docker_build.args(&["--build-arg", "TARGET_ARCH=aarch64"]);
+                }
+                (Some(Architecture::Ppc64Le), "linux/ppc64le", "powerpc64le-unknown-linux-gnu") => {
+                    dockerfile = native_dockerfile.clone();
+                    docker_build.args(&["--build-arg", "TARGET_ARCH=powerpc64le"]);
+                    docker_build.args(&["--build-arg", "QEMU_ARCH=ppc64le"]);
+                }
+                (Some(Architecture::Riscv64), "linux/riscv64", "riscv64gc-unknown-linux-gnu") => {
+                    dockerfile = native_dockerfile.clone();
+                    docker_build.args(&["--build-arg", "TARGET_ARCH=riscv64"]);
+                }
+                (Some(Architecture::S390x), "linux/s390x", "s390x-unknown-linux-gnu") => {
+                    dockerfile = native_dockerfile.clone();
+                    docker_build.args(&["--build-arg", "TARGET_ARCH=s390x"]);
+                }
+                _ => (),
+            }
+        }
 
         if push {
             docker_build.arg("--push");
@@ -259,7 +320,7 @@ pub fn build_docker_image(
             ),
         ]);
 
-        docker_build.args(&["-f", dockerfile]);
+        docker_build.args(&["-f", &dockerfile]);
 
         if gha || progress == "plain" {
             docker_build.args(&["--progress", "plain"]);
@@ -321,6 +382,24 @@ pub fn build_docker_image(
     Ok(())
 }
 
+fn is_armv6() -> bool {
+    cfg!(any(
+        cross_triple = "arm-unknown-linux-gnueabi",
+        cross_triple = "arm-unknown-linux-musleabi"
+    ))
+}
+
+fn is_armv7() -> bool {
+    cfg!(any(
+        cross_triple = "armv7-unknown-linux-gnueabihf",
+        cross_triple = "armv7-unknown-linux-musleabihf"
+    ))
+}
+
+fn note_host_target_detection(msg_info: &mut MessageInfo) -> cross::Result<()> {
+    msg_info.note("using the rust target triple to determine the host triple to determine if the docker platform is native. this may fail if cross-compiling xtask.")
+}
+
 pub fn determine_image_name(
     target: &crate::ImageTarget,
     repository: &str,