diff --git a/Makefile b/Makefile
index e591308..278a109 100644
--- a/Makefile
+++ b/Makefile
@@ -32,11 +32,7 @@ build-nocgo:
 cross-build: build-arm build-arm64 build-nocgo
 
 generate:
-	go run sha1cdblock_amd64_asm.go -out sha1cdblock_amd64.s
-	sed -i 's;&\samd64;&\n// +build !noasm,gc,amd64;g' sha1cdblock_amd64.s
-
-	cd ubc && go run ubc_amd64_asm.go -out ubc_amd64.s
-	sed -i 's;&\samd64;&\n// +build !noasm,gc,amd64;g' ubc/ubc_amd64.s
+	go generate -x ./...
 
 verify: generate
 	git diff --exit-code
diff --git a/sha1cdblock_amd64_asm.go b/asm/asm.go
similarity index 93%
rename from sha1cdblock_amd64_asm.go
rename to asm/asm.go
index 9570273..45c5bf1 100644
--- a/sha1cdblock_amd64_asm.go
+++ b/asm/asm.go
@@ -1,6 +1,3 @@
-//go:build ignore
-// +build ignore
-
 package main
 
 import (
@@ -8,10 +5,18 @@ import (
 	"github.com/mmcloughlin/avo/buildtags"
 	. "github.com/mmcloughlin/avo/operand"
 	. "github.com/mmcloughlin/avo/reg"
-	shared "github.com/pjbgf/sha1cd/internal"
 )
 
-//go:generate go run sha1cdblock_amd64_asm.go -out sha1cdblock_amd64.s
+const (
+	// Constants for the SHA-1 hash function.
+	RoundConst0 = 0x5A827999
+	RoundConst1 = 0x6ED9EBA1
+	RoundConst2 = 0x8F1BBCDC
+	RoundConst3 = 0xCA62C1D6
+
+	// SHA1 processes the input data in chunks. Each chunk contains 64 bytes.
+	Chunk = 64
+)
 
 func main() {
 	Constraint(buildtags.Not("noasm").ToConstraint())
@@ -61,7 +66,7 @@ func main() {
 	}
 
 	// Store message values on the stack.
-	w := AllocLocal(shared.Chunk)
+	w := AllocLocal(Chunk)
 	W := func(r int) Mem { return w.Offset((r % 16) * 4) }
 
 	Comment("len(p) >= chunk")
@@ -161,7 +166,7 @@ func main() {
 		Commentf("ROUND1(%d)", index)
 		LOAD(index)
 		FUNC1(a, b, c, d, e)
-		MIX(a, b, c, d, e, shared.K0)
+		MIX(a, b, c, d, e, RoundConst0)
 		LOADM1(index)
 	}
 
@@ -169,7 +174,7 @@ func main() {
 		Commentf("ROUND1x(%d)", index)
 		SHUFFLE(index)
 		FUNC1(a, b, c, d, e)
-		MIX(a, b, c, d, e, shared.K0)
+		MIX(a, b, c, d, e, RoundConst0)
 		LOADM1(index)
 	}
 
@@ -177,7 +182,7 @@ func main() {
 		Commentf("ROUND2(%d)", index)
 		SHUFFLE(index)
 		FUNC2(a, b, c, d, e)
-		MIX(a, b, c, d, e, shared.K1)
+		MIX(a, b, c, d, e, RoundConst1)
 		LOADM1(index)
 	}
 
@@ -185,7 +190,7 @@ func main() {
 		Commentf("ROUND3(%d)", index)
 		SHUFFLE(index)
 		FUNC3(a, b, c, d, e)
-		MIX(a, b, c, d, e, shared.K2)
+		MIX(a, b, c, d, e, RoundConst2)
 		LOADM1(index)
 	}
 
@@ -193,7 +198,7 @@ func main() {
 		Commentf("ROUND4(%d)", index)
 		SHUFFLE(index)
 		FUNC4(a, b, c, d, e)
-		MIX(a, b, c, d, e, shared.K3)
+		MIX(a, b, c, d, e, RoundConst3)
 		LOADM1(index)
 	}
 
@@ -297,7 +302,7 @@ func main() {
 		ADDL(r, hash[i])
 	}
 
-	ADDQ(I8(shared.Chunk), p_base)
+	ADDQ(I8(Chunk), p_base)
 	CMPQ(p_base, di64)
 	JB(LabelRef("loop"))
 
diff --git a/asm/go.mod b/asm/go.mod
new file mode 100644
index 0000000..5e3fdda
--- /dev/null
+++ b/asm/go.mod
@@ -0,0 +1,15 @@
+module github.com/pjbgf/sha1cd/asm
+
+go 1.21
+
+require (
+	github.com/mmcloughlin/avo v0.6.0
+	github.com/pjbgf/sha1cd v0.0.0-local
+)
+
+require (
+	golang.org/x/mod v0.14.0 // indirect
+	golang.org/x/tools v0.16.1 // indirect
+)
+
+replace github.com/pjbgf/sha1cd => ..
diff --git a/asm/go.sum b/asm/go.sum
new file mode 100644
index 0000000..483bba8
--- /dev/null
+++ b/asm/go.sum
@@ -0,0 +1,8 @@
+github.com/mmcloughlin/avo v0.6.0 h1:QH6FU8SKoTLaVs80GA8TJuLNkUYl4VokHKlPhVDg4YY=
+github.com/mmcloughlin/avo v0.6.0/go.mod h1:8CoAGaCSYXtCPR+8y18Y9aB/kxb8JSS6FRI7mSkvD+8=
+golang.org/x/mod v0.14.0 h1:dGoOF9QVLYng8IHTm7BAyWqCqSheQ5pYWGhzW00YJr0=
+golang.org/x/mod v0.14.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
+golang.org/x/sync v0.5.0 h1:60k92dhOjHxJkrqnwsfl8KuaHbn/5dl0lUPUklKo3qE=
+golang.org/x/sync v0.5.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/tools v0.16.1 h1:TLyB3WofjdOEepBHAU20JdNC1Zbg87elYofWYAY5oZA=
+golang.org/x/tools v0.16.1/go.mod h1:kYVVN6I1mBNoB1OX+noeBjbRk4IUEPa7JJ+TJMEooJ0=
diff --git a/go.mod b/go.mod
index fd5fb11..cd8d1f3 100644
--- a/go.mod
+++ b/go.mod
@@ -1,11 +1,3 @@
 module github.com/pjbgf/sha1cd
 
 go 1.21
-
-require github.com/mmcloughlin/avo v0.6.0
-
-require (
-	golang.org/x/mod v0.17.0 // indirect
-	golang.org/x/sync v0.7.0 // indirect
-	golang.org/x/tools v0.20.0 // indirect
-)
diff --git a/go.sum b/go.sum
index 4dd7891..e69de29 100644
--- a/go.sum
+++ b/go.sum
@@ -1,13 +0,0 @@
-github.com/mmcloughlin/avo v0.6.0 h1:QH6FU8SKoTLaVs80GA8TJuLNkUYl4VokHKlPhVDg4YY=
-github.com/mmcloughlin/avo v0.6.0/go.mod h1:8CoAGaCSYXtCPR+8y18Y9aB/kxb8JSS6FRI7mSkvD+8=
-golang.org/x/mod v0.14.0 h1:dGoOF9QVLYng8IHTm7BAyWqCqSheQ5pYWGhzW00YJr0=
-golang.org/x/mod v0.14.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
-golang.org/x/mod v0.17.0 h1:zY54UmvipHiNd+pm+m0x9KhZ9hl1/7QNMyxXbc6ICqA=
-golang.org/x/mod v0.17.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
-golang.org/x/sync v0.5.0 h1:60k92dhOjHxJkrqnwsfl8KuaHbn/5dl0lUPUklKo3qE=
-golang.org/x/sync v0.7.0 h1:YsImfSBoP9QPYL0xyKJPq0gcaJdG3rInoqxTWbfQu9M=
-golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
-golang.org/x/tools v0.16.1 h1:TLyB3WofjdOEepBHAU20JdNC1Zbg87elYofWYAY5oZA=
-golang.org/x/tools v0.16.1/go.mod h1:kYVVN6I1mBNoB1OX+noeBjbRk4IUEPa7JJ+TJMEooJ0=
-golang.org/x/tools v0.20.0 h1:hz/CVckiOxybQvFw6h7b/q80NTr9IUQb4s1IIzW7KNY=
-golang.org/x/tools v0.20.0/go.mod h1:WvitBU7JJf6A4jOdg4S1tviW9bhUxkgeCui/0JHctQg=
diff --git a/sha1cd.go b/sha1cd.go
index 17f6f84..509569f 100644
--- a/sha1cd.go
+++ b/sha1cd.go
@@ -17,10 +17,11 @@ import (
 	"errors"
 	"hash"
 
-	_ "github.com/mmcloughlin/avo/build"
 	shared "github.com/pjbgf/sha1cd/internal"
 )
 
+//go:generate go run -C asm . -out ../sha1cdblock_amd64.s -pkg $GOPACKAGE
+
 func init() {
 	crypto.RegisterHash(crypto.SHA1, New)
 }
diff --git a/sha1cdblock_amd64.s b/sha1cdblock_amd64.s
index 86f9821..e5e213a 100644
--- a/sha1cdblock_amd64.s
+++ b/sha1cdblock_amd64.s
@@ -1,7 +1,6 @@
-// Code generated by command: go run sha1cdblock_amd64_asm.go -out sha1cdblock_amd64.s. DO NOT EDIT.
+// Code generated by command: go run asm.go -out ../sha1cdblock_amd64.s -pkg sha1cd. DO NOT EDIT.
 
 //go:build !noasm && gc && amd64
-// +build !noasm,gc,amd64
 
 #include "textflag.h"
 
diff --git a/ubc/ubc_amd64_asm.go b/ubc/asm/asm.go
similarity index 99%
rename from ubc/ubc_amd64_asm.go
rename to ubc/asm/asm.go
index b2ba70c..c639c19 100644
--- a/ubc/ubc_amd64_asm.go
+++ b/ubc/asm/asm.go
@@ -1,6 +1,3 @@
-//go:build ignore
-// +build ignore
-
 package main
 
 import (
@@ -10,8 +7,6 @@ import (
 	"github.com/pjbgf/sha1cd/ubc"
 )
 
-//go:generate go run ubc_amd64_asm.go -out ubc_amd64.s
-
 const (
 	DvTypeOffset = 0
 	DvKOffset    = 4
diff --git a/ubc/asm/go.mod b/ubc/asm/go.mod
new file mode 100644
index 0000000..cec3bb4
--- /dev/null
+++ b/ubc/asm/go.mod
@@ -0,0 +1,16 @@
+module github.com/pjbgf/sha1cd/ubc/asm
+
+go 1.21
+
+require (
+	github.com/mmcloughlin/avo v0.6.0
+	github.com/pjbgf/sha1cd v0.0.0-local
+)
+
+require (
+	golang.org/x/mod v0.17.0 // indirect
+	golang.org/x/sync v0.7.0 // indirect
+	golang.org/x/tools v0.20.0 // indirect
+)
+
+replace github.com/pjbgf/sha1cd => ../..
diff --git a/ubc/asm/go.sum b/ubc/asm/go.sum
new file mode 100644
index 0000000..487ec7d
--- /dev/null
+++ b/ubc/asm/go.sum
@@ -0,0 +1,8 @@
+github.com/mmcloughlin/avo v0.6.0 h1:QH6FU8SKoTLaVs80GA8TJuLNkUYl4VokHKlPhVDg4YY=
+github.com/mmcloughlin/avo v0.6.0/go.mod h1:8CoAGaCSYXtCPR+8y18Y9aB/kxb8JSS6FRI7mSkvD+8=
+golang.org/x/mod v0.17.0 h1:zY54UmvipHiNd+pm+m0x9KhZ9hl1/7QNMyxXbc6ICqA=
+golang.org/x/mod v0.17.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
+golang.org/x/sync v0.7.0 h1:YsImfSBoP9QPYL0xyKJPq0gcaJdG3rInoqxTWbfQu9M=
+golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/tools v0.20.0 h1:hz/CVckiOxybQvFw6h7b/q80NTr9IUQb4s1IIzW7KNY=
+golang.org/x/tools v0.20.0/go.mod h1:WvitBU7JJf6A4jOdg4S1tviW9bhUxkgeCui/0JHctQg=
diff --git a/ubc/doc.go b/ubc/ubc.go
similarity index 68%
rename from ubc/doc.go
rename to ubc/ubc.go
index 0090e36..b0b4d76 100644
--- a/ubc/doc.go
+++ b/ubc/ubc.go
@@ -1,3 +1,5 @@
 // ubc package provides ways for SHA1 blocks to be checked for
 // Unavoidable Bit Conditions that arise from crypto analysis attacks.
 package ubc
+
+//go:generate go run -C asm . -out ../ubc_amd64.s -pkg $GOPACKAGE
diff --git a/ubc/ubc_amd64.s b/ubc/ubc_amd64.s
index 0c0f4e4..c77ea77 100644
--- a/ubc/ubc_amd64.s
+++ b/ubc/ubc_amd64.s
@@ -1,7 +1,6 @@
-// Code generated by command: go run ubc_amd64_asm.go -out ubc_amd64.s. DO NOT EDIT.
+// Code generated by command: go run asm.go -out ../ubc_amd64.s -pkg ubc. DO NOT EDIT.
 
 //go:build !noasm && gc && amd64
-// +build !noasm,gc,amd64
 
 #include "textflag.h"