Add concept of a native Dockerfile.

[Alexhuszagh]

No description provided.

[Alexhuszagh]

The idea behind this is so we can provide native toolchains if the image platform and the cross-compilation target are the same. This simplifies our logic for say, linux/arm64 images for an aarch64-unknown-linux-gnu toolchain. There's still some work to do, however:

1. Need to change x86_64-unknown-linux-gnu to actually work when cross-compiled.
2. Change i686-unknown-linux-gnu and i586-unknown-linux-gnu to allow use from a non-x86_64 image.
3. Test the Native toolchain on a non-x86_64 image.

We might require slightly more complex logic for i586/i686 since the default package we'd install for x86_64 (g++-x86-64-linux-gnu) I don't believe is multilib (although I could be wrong here).

[Emilgardis]

I'm not sure I understand what this does and how it differs. How is it used?

[Alexhuszagh]

I'm not sure I understand what this does and how it differs. How is it used?

Say if I want to build aarch64-unknown-linux-gnu for an image running Ubuntu:20.04 on linux/arm64: I just want to install GCC, G++, glibc, and don't want a cross-compiler: I just want the same logic as the current Dockerfile.x86_64-unknown-linux-gnu. And doing this generic logic for every possible host is a lot: we can just make a generic native Dockerfile and use it for every native toolchain for the image.

[Emilgardis]

with buildkit it's possible to do conditional stages, I think that could help to not use a script file

# arm64-specific stage
FROM base AS build-arm64
RUN echo "This stage is used on arm64"

# amd64-specific stage
FROM base AS build-amd64
RUN echo "This stage is used on amd64 (x86)"

# common steps
FROM build-${TARGETARCH} AS build
RUN echo "This stage is used on all architectures"

for example

[Alexhuszagh]

with buildkit it's possible to do conditional stages, I think that could help to not use a script file

# arm64-specific stage
FROM base AS build-arm64
RUN echo "This stage is used on arm64"

# amd64-specific stage
FROM base AS build-amd64
RUN echo "This stage is used on amd64 (x86)"

# common steps
FROM build-${TARGETARCH} AS build
RUN echo "This stage is used on all architectures"

for example

In retrospect, I don't think we need a script (just native/non-native) unless we want to support targets where we have to build from source (which I think we can omit) or use Debian repositories only for a different architecture (specifically, MIPS).

[Alexhuszagh]

bors try --target x86_64-unknown-linux-gnu

[bors]

try

Build succeeded:

• conclusion

[Emilgardis]

looks good, I'm just not sure I like the naming.

maybe same-platform?

I'd also like it if with this pr that the image is made available and used when possible.

[Alexhuszagh]

Based on comments elsewhere, I should clarify that this is not used to publish a ghcr.io/cross-rs/native:$tag image: it is meant so Dockerfile.native is used for ghcr.io/cross-rs/x86_64-unknown-linux-gnu:$tag on linux/amd64 and ghcr.io/cross-rs/aarch64-unknown-linux-gnu:$tag on linux/arm64, and that Dockerfile.x86_64-unknown-linux-gnu is only used if the platform is not linux/amd64 (same with Dockerfile.aarch64-unknown-linux-gnu and linux/arm64).

When building the image, we change the Dockerfile used for the build. If the image architecture is the same as the target architecture, and the target triple is *-linux-gnu, then use Dockerfile.native. Otherwise, use the normal Dockerfile. This is required since packages like g++ are not for x86_64 on a linux/arm64 platform, and packages like g++-x86-64-linux-gnu and g++-aarch64-linux-gnu are not available on linux/amd64 and linux/arm64, respectively.

[bors]

Build failed:

• conclusion

[Emilgardis]

bors try --target x86_64-unknown-linux-gnu*

[bors]

try

Build succeeded:

• conclusion

[Alexhuszagh]

This is done after the shared code, which will be nice when creating a base image but also for cached layers even before then.

[Emilgardis]

forgot about this

looks good

bors r+

[Emilgardis]

bors cancel

[bors]

Canceled.

[Alexhuszagh]

bors r=Emilgardis

[bors]

Build failed:

• conclusion

[Alexhuszagh]

This target did not change and passed the last time...
https://github.com/cross-rs/cross/actions/runs/3207655589/jobs/5242799975#step:12:146

[Emilgardis]

I see no reason for why it would not work now except for some filesystem error

lets try again

bors r+

[Emilgardis]

bors cancel

bors retry

[bors]

Canceled.

[Emilgardis]

bors r+

doesn't seem like it got queued https://app.bors.tech/repositories/45789

[bors]

Build succeeded:

• conclusion