Something is not right with `GOARM`

[AlekSi]

GOARM value is correct for linux/arm/v5 variant:

$ docker rmi golang; docker run -q --rm --platform=linux/arm/v5 golang go env GOARM
[…]
5

However, it is not correct for linux/arm/v7:

$ docker rmi golang; docker run -q --rm --platform=linux/arm/v7 golang go env GOARM
[…]
6

[yosifkit]

Upstream go only publishes armv6 binaries (https://go.dev/dl/), so that is what is currently used:

golang/versions.sh

Line 77 in e787bff

# the published binaries only support glibc, which translates to Debian, so the "correct" binary for v7 is v6 (TODO find some way to reasonably benchmark the compiler on a proper v7 chip and determine whether recompiling for GOARM=7 is worthwhile)

[AlekSi]

determine whether recompiling for GOARM=7 is worthwhile

I think it is worth doing it just to avoid confusion. I used that image as a base to build ARM v7 binaries that turned out to be v6. It means that every user of that image has to be aware of it and apply a workaround.

[tianon]

Is there a significant performance difference between compiling with GOARM=6 vs GOARM=7?
(I don't think the Go project itself would've chosen lightly to only publish v6.)

More generally, I'd honestly recommend users should always be explicit about the full set of GOOS, GOARCH, and GOARM, especially in the case of building binaries for publishing.

[AlekSi]

I'd honestly recommend users should always be explicit about the full set of GOOS, GOARCH, and GOARM, especially in the case of building binaries for publishing.

That somewhat contradicts the recommendations of the Go team. There is no need to set those variables if compilation is performed on the host – autodetection works in this case. And I would expect BuildKit/QEMU-powered builds to be indistinguishable from builds on the host – and they would be, if not this issue with the base image.

Edit:
To put it another way, for any compiler, I would expect docker run --platform=linux/arm/v7 my-compiler ... to produce the native binary for arm/v7 unless the compiler's cross-compilation flags are set explicitly. That's true for Go, too, but not for this Docker image.

[tianon]

That's true for Go, too, but not for this Docker image.

For Go built from source, yes, but not for Go downloaded from https://go.dev/dl/ (which only publishes armv6, so that's what you'd download/use on armv7).

However, I remembered today that 1.21 has go.env so we can override this default for the install without recompiling, so I'm going to make a PR doing that shortly. 👀