Re: [ptxdist] Go in ptxdist

[Michael Olbrich <m.olbrich@pengutronix.de>]

On Tue, Oct 04, 2016 at 05:23:25PM +0200, Clemens Gruber wrote:
> Hi,
> 
> I'd like to start a discussion about implementing support for Go
> language projects in ptxdist. https://golang.org
> 
> The nice thing about the recent Go versions is that cross compilation is
> possible without recompiling Go for the target architecture.
> You can use the Go version from your host and cross compile to the
> supported target architectures and operating system.
> Go binaries are statically compiled, so we would only need Go on the
> host system.
> 
> To cross-compile an ARMv7 binary, you just call:
> env GOOS=linux GOARCH=arm GOARM=7 go build helloworld.go
> Tested with Go 1.7.1 on ArchLinux and cross-compiled binary is running
> successfully on an i.MX6Q.
> If you are wondering about my use case:
> I am implementing a Webapp backend with Revel (github.com/revel/revel)
> for the admin interface to our embedded product and Go is a fine
> language for writing server software.
> 
> --
> 
> What are your thoughts about this?

In PTXdist things should be reproducible. So relying on a compiler for
target code in the host system is not a good idea.
I'm not familiar with Go. Would creating a 'host-go' package be feasible?

> --
> 
> Maybe:
> Having a new FOO_CONF_TOOL value "go" similar to "python3" and adding
> additional case statements to scripts/lib/ptxd_make_world_*.sh and
> building the Go files there, either via go build or using go install.
> 
> We probably need a static mapping from supported toolchain ABIs to
> GOARCH (and GOARM) values:
> aarch64-v8a-linux-gnu       -> GOARCH=arm64
> arm-1136jfs-linux-gnueabi   -> GOARCH=arm GOARM=5

Are you sure that this is correct? The compiler will produce ARMv6 code.

> arm-1136jfs-linux-gnueabihf -> GOARCH=arm GOARM=6
> arm-cortexa8-linux-gnueabi  -> GOARCH=arm GOARM=5

same here.

> arm-cortexa8-linux-gnueabihf-> GOARCH=arm GOARM=7
> arm-v5te-linux-gnueabi      -> GOARCH=arm GOARM=5
> arm-v7a-linux-gnueabi       -> GOARCH=arm GOARM=5

and here.

> arm-v7a-linux-gnueabihf     -> GOARCH=arm GOARM=7

I'd prefer it if we cleaned up the arm architecture stuff in
architecture.in to make this explicit.

> i586-unknown-linux-gnu      -> GOARCH=386
> i686-atom-linux-gnu         -> GOARCH=386
> x86_64-unknown-linux-gnu    -> GOARCH=amd64
> 
> Go supports >=ARMv6 builds with hardfloat only, so I'd fall back to
> building ARMv5 binaries for ARMv6/7 softfloat configurations.

Are you sure this means it cannot create armv6/7 softfloat?

> The mininum size of the generated binaries is still rather large, but
> this will improve in Go 1.8: https://blog.golang.org/go1.7-binary-size
> (At the moment, my hello world example is 927KB if stripped, as it
> includes the statically linked runtime)
> I probably would not use it for small little tools running only for
> short time periods, but for long-running server software, it's fine.

Michael

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