internal/rosa: configurable architecture

This enables curing via binfmt.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/rosa.go

@@ -4,7 +4,6 @@ package rosa
 import (
 	"errors"
 	"path"
-	"runtime"
 	"slices"
 	"strconv"
 	"strings"
@@ -54,10 +53,9 @@ var (
 	AbsSystem = fhs.AbsRoot.Append("system")
 )
 
-// linuxArch returns the architecture name used by linux corresponding to
-// [runtime.GOARCH].
+// linuxArch returns the architecture name used by linux corresponding to arch.
 func linuxArch() string {
-	switch runtime.GOARCH {
+	switch arch {
 	case "amd64":
 		return "x86_64"
 	case "arm64":
@@ -66,11 +64,11 @@ func linuxArch() string {
 		return "riscv64"
 
 	default:
-		panic("unsupported target " + runtime.GOARCH)
+		panic("unsupported target " + arch)
 	}
 }
 
-// triplet returns the Rosa OS host triple corresponding to [runtime.GOARCH].
+// triplet returns the Rosa OS host triple corresponding to arch.
 func triplet() string {
 	return linuxArch() + "-rosa-linux-musl"
 }
@@ -80,9 +78,9 @@ type perArch[T any] map[string]T
 
 // unwrap returns the value for the current architecture.
 func (p perArch[T]) unwrap() T {
-	v, ok := p[runtime.GOARCH]
+	v, ok := p[arch]
 	if !ok {
-		panic("unsupported target " + runtime.GOARCH)
+		panic("unsupported target " + arch)
 	}
 	return v
 }
@@ -268,7 +266,7 @@ func (t Toolchain) New(
 		support = append(support, extra...)
 		support = append(support, cureEtc{})
 		if t == toolchainStage0 {
-			support = append(support, NewStage0())
+			support = append(support, t.Load(stage0Dist))
 		} else {
 			support = append(support, _toolchainBusybox.New("gentoo", 0, nil, nil, nil, `
 tar -C /work -xf /usr/src/stage3.tar.xz