cmd/dist: GOHOSTARCH defaults to kernel arch even when it does not match userspace arch

[jefferyto]

What version of Go are you using (go version)?

$ go version
go version go1.15.15 linux/arm

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="arm"
GOBIN=""
GOCACHE="/home/jeff/.cache/go-build"
GOENV="/home/jeff/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="arm"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/jeff/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/jeff/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go-1.15"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go-1.15/pkg/tool/linux_arm"
GCCGO="gccgo"
GOARM="6"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -marm -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build431512454=/tmp/go-build -gno-record-gcc-switches"

What did you do?

This was first raised in openwrt/packages#18584.

With Raspbian / Raspberry Pi OS and later models of Raspberry Pi, it is possible to boot a 64-bit kernel with an otherwise completely 32-bit userland (by setting arm_64bit=1 in config.txt).

I have replicated this setup with a Raspberry Pi 3 Model B and Raspberry Pi OS Lite (32-bit, based on Debian 11 bullseye):

$ uname -a
Linux raspberrypi 5.15.32-v8+ #1538 SMP PREEMPT Thu Mar 31 19:40:39 BST 2022 aarch64 GNU/Linux

And I am trying to compile the latest release of Go (1.18.2) using the distro packaged Go (1.15.15) as bootstrap.

What did you expect to see?

Go compiled with no extra flags/environment variables needed.

What did you see instead?

A build error always occurs:

$ ./make.bash
Building Go cmd/dist using /usr/lib/go-1.15. (go1.15.15 linux/arm)
Building Go toolchain1 using /usr/lib/go-1.15.
Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.
Building Go toolchain2 using go_bootstrap and Go toolchain1.
Building Go toolchain3 using go_bootstrap and Go toolchain2.
Building packages and commands for linux/arm64.
# runtime/cgo
In file included from _cgo_export.c:4:
cgo-gcc-export-header-prolog:25:14: error: size of array '_check_for_64_bit_pointer_matching_GoInt' is negative
go tool dist: FAILED: /media/Downloads/go/pkg/tool/linux_arm64/go_bootstrap install -gcflags=all= -ldflags=all= std cmd: exit status 2

Compilation continues for a while after the runtime/cgo error; it does not appear to be the direct cause of the go tool dist error.

(I have also seen compilation exit earlier due to an error occurring at the Building Go toolchain3 using go_bootstrap and Go toolchain2. stage, though I have not been able to replicate this consistently and am not certain it is related to this issue.)

This error appears to be caused by GOHOSTARCH defaulting to arm64 (based on the output of uname -m) even though the userspace is 32-bit only. If I set GOHOSTARCH=arm, then compilation succeeds.

From the installation documentation it appears that explicitly setting GOHOSTARCH is probably necessary/correct, but I wonder: why base GOHOSTARCH on the kernel arch when GOHOSTARCH from bootstrap Go appears to be a safer default value?