internal/poly1305: Port sum_amd64.s to Avo

This implementation utilizes the same registers found in the reference
implementation, aiming to produce a minimal semantic diff between the
Avo-generated output and the original hand-written assembly.

To verify the Avo implementation, the reference and Avo-generated
assembly files are fed to `go tool asm`, capturing the debug output into
corresponding temp files. The debug output contains supplementary
metadata (line numbers, instruction offsets, and source file references)
that must be removed in order to obtain a semantic diff of the two
files. This is accomplished via a small utility script written in awk.

Commands used to verify Avo output:

GOROOT=$(go env GOROOT)
ASM_PATH="internal/poly1305/sum_amd64.s"
REFERENCE="b2d3a6a4b4d36521cd7f653879cf6981e7c5c340"

go tool asm -o /dev/null -I "$GOROOT"/src/runtime -debug \
  <(git cat-file -p "$REFERENCE:$ASM_PATH") \
  > /tmp/reference.s

go tool asm -o /dev/null -I "$GOROOT"/src/runtime -debug \
  "$ASM_PATH" \
  > /tmp/avo.s

normalize(){
  awk '{
    $1=$2=$3="";
    print substr($0,4)
  }'
}

diff <(normalize < /tmp/reference.s) <(normalize < /tmp/avo.s)

Change-Id: I80212c95d1b05335d7f6b73a3030b6f812f6105b
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/600035
Reviewed-by: Roland Shoemaker <roland@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

internal/poly1305/_asm/go.mod

@@ -0,0 +1,15 @@
+module internal/poly1305/_asm
+
+go 1.23
+
+require (
+	github.com/mmcloughlin/avo v0.6.0
+	golang.org/x/crypto v0.26.0
+)
+
+require (
+	golang.org/x/mod v0.20.0 // indirect
+	golang.org/x/sync v0.8.0 // indirect
+	golang.org/x/sys v0.24.0 // indirect
+	golang.org/x/tools v0.24.0 // indirect
+)

internal/poly1305/_asm/go.sum

@@ -0,0 +1,12 @@
+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/crypto v0.26.0 h1:RrRspgV4mU+YwB4FYnuBoKsUapNIL5cohGAmSH3azsw=
+golang.org/x/crypto v0.26.0/go.mod h1:GY7jblb9wI+FOo5y8/S2oY4zWP07AkOJ4+jxCqdqn54=
+golang.org/x/mod v0.20.0 h1:utOm6MM3R3dnawAiJgn0y+xvuYRsm1RKM/4giyfDgV0=
+golang.org/x/mod v0.20.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
+golang.org/x/sync v0.8.0 h1:3NFvSEYkUoMifnESzZl15y791HH1qU2xm6eCJU5ZPXQ=
+golang.org/x/sync v0.8.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/sys v0.24.0 h1:Twjiwq9dn6R1fQcyiK+wQyHWfaz/BJB+YIpzU/Cv3Xg=
+golang.org/x/sys v0.24.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/tools v0.24.0 h1:J1shsA93PJUEVaUSaay7UXAyE8aimq3GW0pjlolpa24=
+golang.org/x/tools v0.24.0/go.mod h1:YhNqVBIfWHdzvTLs0d8LCuMhkKUgSUKldakyV7W/WDQ=

internal/poly1305/_asm/sum_amd64_asm.go

@@ -0,0 +1,126 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	. "github.com/mmcloughlin/avo/build"
+	. "github.com/mmcloughlin/avo/operand"
+	. "github.com/mmcloughlin/avo/reg"
+	_ "golang.org/x/crypto/sha3"
+)
+
+//go:generate go run . -out ../sum_amd64.s -pkg poly1305
+
+func main() {
+	Package("golang.org/x/crypto/internal/poly1305")
+	ConstraintExpr("gc,!purego")
+	update()
+	Generate()
+}
+
+func update() {
+	Implement("update")
+
+	Load(Param("state"), RDI)
+	MOVQ(NewParamAddr("msg_base", 8), RSI)
+	MOVQ(NewParamAddr("msg_len", 16), R15)
+
+	MOVQ(Mem{Base: DI}.Offset(0), R8)   // h0
+	MOVQ(Mem{Base: DI}.Offset(8), R9)   // h1
+	MOVQ(Mem{Base: DI}.Offset(16), R10) // h2
+	MOVQ(Mem{Base: DI}.Offset(24), R11) // r0
+	MOVQ(Mem{Base: DI}.Offset(32), R12) // r1
+
+	CMPQ(R15, Imm(16))
+	JB(LabelRef("bytes_between_0_and_15"))
+
+	Label("loop")
+	POLY1305_ADD(RSI, R8, R9, R10)
+
+	Label("multiply")
+	POLY1305_MUL(R8, R9, R10, R11, R12, RBX, RCX, R13, R14)
+	SUBQ(Imm(16), R15)
+	CMPQ(R15, Imm(16))
+	JAE(LabelRef("loop"))
+
+	Label("bytes_between_0_and_15")
+	TESTQ(R15, R15)
+	JZ(LabelRef("done"))
+	MOVQ(U32(1), RBX)
+	XORQ(RCX, RCX)
+	XORQ(R13, R13)
+	ADDQ(R15, RSI)
+
+	Label("flush_buffer")
+	SHLQ(Imm(8), RBX, RCX)
+	SHLQ(Imm(8), RBX)
+	MOVB(Mem{Base: SI}.Offset(-1), R13B)
+	XORQ(R13, RBX)
+	DECQ(RSI)
+	DECQ(R15)
+	JNZ(LabelRef("flush_buffer"))
+
+	ADDQ(RBX, R8)
+	ADCQ(RCX, R9)
+	ADCQ(Imm(0), R10)
+	MOVQ(U32(16), R15)
+	JMP(LabelRef("multiply"))
+
+	Label("done")
+	MOVQ(R8, Mem{Base: DI}.Offset(0))
+	MOVQ(R9, Mem{Base: DI}.Offset(8))
+	MOVQ(R10, Mem{Base: DI}.Offset(16))
+	RET()
+}
+
+func POLY1305_ADD(msg, h0, h1, h2 GPPhysical) {
+	ADDQ(Mem{Base: msg}.Offset(0), h0)
+	ADCQ(Mem{Base: msg}.Offset(8), h1)
+	ADCQ(Imm(1), h2)
+	LEAQ(Mem{Base: msg}.Offset(16), msg)
+}
+
+func POLY1305_MUL(h0, h1, h2, r0, r1, t0, t1, t2, t3 GPPhysical) {
+	MOVQ(r0, RAX)
+	MULQ(h0)
+	MOVQ(RAX, t0)
+	MOVQ(RDX, t1)
+	MOVQ(r0, RAX)
+	MULQ(h1)
+	ADDQ(RAX, t1)
+	ADCQ(Imm(0), RDX)
+	MOVQ(r0, t2)
+	IMULQ(h2, t2)
+	ADDQ(RDX, t2)
+
+	MOVQ(r1, RAX)
+	MULQ(h0)
+	ADDQ(RAX, t1)
+	ADCQ(Imm(0), RDX)
+	MOVQ(RDX, h0)
+	MOVQ(r1, t3)
+	IMULQ(h2, t3)
+	MOVQ(r1, RAX)
+	MULQ(h1)
+	ADDQ(RAX, t2)
+	ADCQ(RDX, t3)
+	ADDQ(h0, t2)
+	ADCQ(Imm(0), t3)
+
+	MOVQ(t0, h0)
+	MOVQ(t1, h1)
+	MOVQ(t2, h2)
+	ANDQ(Imm(3), h2)
+	MOVQ(t2, t0)
+	ANDQ(I32(-4), t0)
+	ADDQ(t0, h0)
+	ADCQ(t3, h1)
+	ADCQ(Imm(0), h2)
+	SHRQ(Imm(2), t3, t2)
+	SHRQ(Imm(2), t3)
+	ADDQ(t2, h0)
+	ADCQ(t3, h1)
+	ADCQ(Imm(0), h2)
+}