7 files changed, 50 insertions, 9 deletions
diff --git a/internal/rosa/git.go b/internal/rosa/git.go
index 70d5b6f8..19fb6448 100644
--- a/internal/rosa/git.go
+++ b/internal/rosa/git.go
@@ -25,6 +25,7 @@ func (t Toolchain) NewViaGit(
 
 		HostNet: true,
 		Paths:   []pkg.ExecPath{resolvconf()},
+		NoArch:  true,
 	}, &GenericHelper{
 		Build: `
 git \
diff --git a/internal/rosa/meson.go b/internal/rosa/meson.go
index 97262fbb..25291dd0 100644
--- a/internal/rosa/meson.go
+++ b/internal/rosa/meson.go
@@ -65,6 +65,10 @@ func (attr *MesonHelper) isPython() bool {
 
 // script generates the cure script.
 func (attr *MesonHelper) script(t Toolchain, name string) string {
+	if t.cross() {
+		panic(CrossError(name))
+	}
+
 	if attr == nil {
 		attr = new(MesonHelper)
 	}
diff --git a/internal/rosa/package/nss.az b/internal/rosa/package/nss.az
index 115e5667..a7e1b6f1 100644
--- a/internal/rosa/package/nss.az
+++ b/internal/rosa/package/nss.az
@@ -37,4 +37,6 @@ buildcatrust \
 
 		buildcatrust,
 	];
+
+	cross = nil;
 }
diff --git a/internal/rosa/perl.go b/internal/rosa/perl.go
index 705b1b8d..55c17916 100644
--- a/internal/rosa/perl.go
+++ b/internal/rosa/perl.go
@@ -29,7 +29,11 @@ func (*MakeMakerHelper) scriptEarly() string { return "" }
 func (*MakeMakerHelper) wantsDir() (string, bool) { return "", false }
 
 // script generates Makefile.PL-based build and test commands.
-func (attr *MakeMakerHelper) script(t Toolchain, _ string) string {
+func (attr *MakeMakerHelper) script(t Toolchain, name string) string {
+	if t.cross() {
+		panic(CrossError(name))
+	}
+
 	if attr == nil {
 		attr = new(MakeMakerHelper)
 	}
diff --git a/internal/rosa/python.go b/internal/rosa/python.go
index 54022bd7..e97ded49 100644
--- a/internal/rosa/python.go
+++ b/internal/rosa/python.go
@@ -50,6 +50,10 @@ func (*PipHelper) wantsDir() (string, bool) { return `"$(mktemp -d)"`, false }
 
 // script generates the pip3 install command.
 func (attr *PipHelper) script(t Toolchain, name string) string {
+	if t.cross() {
+		panic(CrossError(name))
+	}
+
 	if attr == nil {
 		attr = new(PipHelper)
 	}
diff --git a/internal/rosa/rosa.go b/internal/rosa/rosa.go
index e83d7097..2241788f 100644
--- a/internal/rosa/rosa.go
+++ b/internal/rosa/rosa.go
@@ -267,8 +267,9 @@ function apply {
 	}
 
 	return t.New(name+"-src", Unversioned, nil, &PackageAttr{
-		Paths: paths,
-		Tools: P{_patch},
+		Paths:  paths,
+		Tools:  P{_patch},
+		NoArch: true,
 	}, &GenericHelper{
 		Build: buf.String(),
 	})
@@ -302,7 +303,7 @@ type Helper interface {
 
 // PackageAttr holds build-system-agnostic attributes.
 type PackageAttr struct {
-	// Measure output if populated. Required by [THostNet].
+	// Measure output if populated. Required by HostNet.
 	KnownChecksum *pkg.Checksum
 
 	// Mount the source tree writable.
@@ -337,6 +338,8 @@ type PackageAttr struct {
 	// Whether to create [pkg.KindExecNet] instead of [pkg.KindExec].
 	HostNet bool
 
+	// Whether the [Helper] behaves identically across all architectures.
+	NoArch bool
 	// Inputs added only during cross-compilation.
 	Cross P
 	// Native utilities used by the build process.
@@ -405,6 +408,10 @@ func (t Toolchain) New(
 		attr = new(PackageAttr)
 	}
 
+	if attr.NoArch {
+		t = t.native()
+	}
+
 	if attr.Std && !t.stage.isStd() {
 		panic(BootstrapError(name))
 	}
@@ -640,6 +647,17 @@ ln -s ../bin /usr/`
 	)
 }
 
+// A CrossError refers to a package that does not support cross-compilation and
+// is panicked by the helper implementation.
+type CrossError string
+
+func (e CrossError) Error() string {
+	return "package " + strconv.Quote(string(e)) +
+		" does not support cross-compilation"
+}
+
+var _ error = CrossError("")
+
 // GenericHelper directly passes build script segments for invocations of
 // one-off build scripts too specific to fit into any other [Helper]
 // implementation, but can still benefit from [Toolchain.New].
@@ -677,14 +695,21 @@ func (attr *GenericHelper) wantsDir() (string, bool) {
 }
 
 // script concatenates specified segments.
-func (attr *GenericHelper) script(t Toolchain, _ string) string {
+func (attr *GenericHelper) script(t Toolchain, name string) string {
 	if attr == nil {
 		attr = new(GenericHelper)
 	}
 
 	script := attr.Build
 	if t.cross() {
-		script = attr.Cross + script
+		if attr.Cross == "" {
+			panic(CrossError(name))
+		}
+		cross := attr.Cross
+		if cross == "\x00" {
+			cross = ""
+		}
+		script = cross + script
 	}
 	if t.opts&OptSkipCheck == 0 {
 		script += attr.Check
diff --git a/internal/rosa/state.go b/internal/rosa/state.go
index 18f9a6f3..bda8d32e 100644
--- a/internal/rosa/state.go
+++ b/internal/rosa/state.go
@@ -1100,10 +1100,10 @@ func (ctx *evalContext) pf(
 		overlay string
 		join    bool
 
-		tools, inputs, cross, extra azalea.Array
+		tools, inputs, extra azalea.Array
 
-		runtimes  = azalea.Array{}
-		bootstrap = true
+		cross, runtimes = azalea.Array{}, azalea.Array{}
+		bootstrap       = true
 	)
 	if err = args.Apply(map[unique.Handle[azalea.Ident]]any{
 		k("description"): &meta.Description,
@@ -1144,6 +1144,7 @@ func (ctx *evalContext) pf(
 		return
 	}
 	attr.Std = !bootstrap
+	attr.NoArch = cross == nil
 	var inputsH, extraH P
 	if inputsH, err = toHandles(inputs); err != nil {
 		return