Use mod vendor for vendored directory (backwards compatible)

vendor/golang.org/x/crypto/salsa20/salsa/LICENSE

@@ -1,27 +0,0 @@
-Copyright (c) 2009 The Go Authors. All rights reserved.
-
-Redistribution and use in source and binary forms, with or without
-modification, are permitted provided that the following conditions are
-met:
-
-   * Redistributions of source code must retain the above copyright
-notice, this list of conditions and the following disclaimer.
-   * Redistributions in binary form must reproduce the above
-copyright notice, this list of conditions and the following disclaimer
-in the documentation and/or other materials provided with the
-distribution.
-   * Neither the name of Google Inc. nor the names of its
-contributors may be used to endorse or promote products derived from
-this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

vendor/golang.org/x/crypto/salsa20/salsa/salsa2020_amd64.s

@@ -5,29 +5,23 @@
 // +build amd64,!appengine,!gccgo
 
 // This code was translated into a form compatible with 6a from the public
-// domain sources in SUPERCOP: http://bench.cr.yp.to/supercop.html
+// domain sources in SUPERCOP: https://bench.cr.yp.to/supercop.html
 
 // func salsa2020XORKeyStream(out, in *byte, n uint64, nonce, key *byte)
-TEXT ·salsa2020XORKeyStream(SB),0,$512-40
+// This needs up to 64 bytes at 360(SP); hence the non-obvious frame size.
+TEXT ·salsa2020XORKeyStream(SB),0,$456-40 // frame = 424 + 32 byte alignment
 	MOVQ out+0(FP),DI
 	MOVQ in+8(FP),SI
 	MOVQ n+16(FP),DX
 	MOVQ nonce+24(FP),CX
 	MOVQ key+32(FP),R8
 
-	MOVQ SP,R11
-	MOVQ $31,R9
-	NOTQ R9
-	ANDQ R9,SP
-	ADDQ $32,SP
+	MOVQ SP,R12
+	MOVQ SP,R9
+	ADDQ $31, R9
+	ANDQ $~31, R9
+	MOVQ R9, SP
 
-	MOVQ R11,352(SP)
-	MOVQ R12,360(SP)
-	MOVQ R13,368(SP)
-	MOVQ R14,376(SP)
-	MOVQ R15,384(SP)
-	MOVQ BX,392(SP)
-	MOVQ BP,400(SP)
 	MOVQ DX,R9
 	MOVQ CX,DX
 	MOVQ R8,R10
@@ -133,7 +127,7 @@ TEXT ·salsa2020XORKeyStream(SB),0,$512-40
 	SHRQ $32,CX
 	MOVL DX,16(SP)
 	MOVL CX, 36 (SP)
-	MOVQ R9,408(SP)
+	MOVQ R9,352(SP)
 	MOVQ $20,DX
 	MOVOA 64(SP),X0
 	MOVOA 80(SP),X1
@@ -650,7 +644,7 @@ TEXT ·salsa2020XORKeyStream(SB),0,$512-40
 	MOVL CX,244(DI)
 	MOVL R8,248(DI)
 	MOVL R9,252(DI)
-	MOVQ 408(SP),R9
+	MOVQ 352(SP),R9
 	SUBQ $256,R9
 	ADDQ $256,SI
 	ADDQ $256,DI
@@ -662,13 +656,13 @@ TEXT ·salsa2020XORKeyStream(SB),0,$512-40
 	CMPQ R9,$64
 	JAE NOCOPY
 	MOVQ DI,DX
-	LEAQ 416(SP),DI
+	LEAQ 360(SP),DI
 	MOVQ R9,CX
 	REP; MOVSB
-	LEAQ 416(SP),DI
-	LEAQ 416(SP),SI
+	LEAQ 360(SP),DI
+	LEAQ 360(SP),SI
 	NOCOPY:
-	MOVQ R9,408(SP)
+	MOVQ R9,352(SP)
 	MOVOA 48(SP),X0
 	MOVOA 0(SP),X1
 	MOVOA 16(SP),X2
@@ -867,7 +861,7 @@ TEXT ·salsa2020XORKeyStream(SB),0,$512-40
 	MOVL R8,44(DI)
 	MOVL R9,28(DI)
 	MOVL AX,12(DI)
-	MOVQ 408(SP),R9
+	MOVQ 352(SP),R9
 	MOVL 16(SP),CX
 	MOVL  36 (SP),R8
 	ADDQ $1,CX
@@ -886,14 +880,7 @@ TEXT ·salsa2020XORKeyStream(SB),0,$512-40
 	REP; MOVSB
 	BYTESATLEAST64:
 	DONE:
-	MOVQ 352(SP),R11
-	MOVQ 360(SP),R12
-	MOVQ 368(SP),R13
-	MOVQ 376(SP),R14
-	MOVQ 384(SP),R15
-	MOVQ 392(SP),BX
-	MOVQ 400(SP),BP
-	MOVQ R11,SP
+	MOVQ R12,SP
 	RET
 	BYTESATLEAST65:
 	SUBQ $64,R9

vendor/golang.org/x/crypto/salsa20/salsa/salsa20_amd64.go

@@ -13,11 +13,12 @@ package salsa
 func salsa2020XORKeyStream(out, in *byte, n uint64, nonce, key *byte)
 
 // XORKeyStream crypts bytes from in to out using the given key and counters.
-// In and out may be the same slice but otherwise should not overlap. Counter
+// In and out must overlap entirely or not at all. Counter
 // contains the raw salsa20 counter bytes (both nonce and block counter).
 func XORKeyStream(out, in []byte, counter *[16]byte, key *[32]byte) {
 	if len(in) == 0 {
 		return
 	}
+	_ = out[len(in)-1]
 	salsa2020XORKeyStream(&out[0], &in[0], uint64(len(in)), &counter[0], &key[0])
 }

vendor/golang.org/x/crypto/salsa20/salsa/salsa20_ref.go

@@ -203,7 +203,7 @@ func core(out *[64]byte, in *[16]byte, k *[32]byte, c *[16]byte) {
 }
 
 // XORKeyStream crypts bytes from in to out using the given key and counters.
-// In and out may be the same slice but otherwise should not overlap. Counter
+// In and out must overlap entirely or not at all. Counter
 // contains the raw salsa20 counter bytes (both nonce and block counter).
 func XORKeyStream(out, in []byte, counter *[16]byte, key *[32]byte) {
 	var block [64]byte