cmd/internal/obj: make x86's asmbuf a local variable

The x86 assembler requires a buffer to build
variable-length instructions.
It used to be an obj.Link field.
That doesn't play nicely with concurrent assembly.
Move the AsmBuf type to the x86 package,
where it belongs anyway,
and make it a local variable.

Passes toolstash-check -all.
No compiler performance impact.

Updates #15756

Change-Id: I8014e52145380bfd378ee374a0c971ee5bada917
Reviewed-on: https://go-review.googlesource.com/38663
Run-TryBot: Josh Bleecher Snyder <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: josharian

src/cmd/internal/obj/link.go

@@ -740,7 +740,6 @@ type Link struct {
 	Rep           int
 	Repn          int
 	Lock          int
-	AsmBuf        AsmBuf // instruction buffer for x86
 	Instoffset    int64
 	Autosize      int32
 	Armsize       int32
@@ -878,96 +877,3 @@ func (h *HeadType) String() string {
 	}
 	return fmt.Sprintf("HeadType(%d)", *h)
 }
-
-// AsmBuf is a simple buffer to assemble variable-length x86 instructions into.
-type AsmBuf struct {
-	buf [100]byte
-	off int
-}
-
-// Put1 appends one byte to the end of the buffer.
-func (a *AsmBuf) Put1(x byte) {
-	a.buf[a.off] = x
-	a.off++
-}
-
-// Put2 appends two bytes to the end of the buffer.
-func (a *AsmBuf) Put2(x, y byte) {
-	a.buf[a.off+0] = x
-	a.buf[a.off+1] = y
-	a.off += 2
-}
-
-// Put3 appends three bytes to the end of the buffer.
-func (a *AsmBuf) Put3(x, y, z byte) {
-	a.buf[a.off+0] = x
-	a.buf[a.off+1] = y
-	a.buf[a.off+2] = z
-	a.off += 3
-}
-
-// Put4 appends four bytes to the end of the buffer.
-func (a *AsmBuf) Put4(x, y, z, w byte) {
-	a.buf[a.off+0] = x
-	a.buf[a.off+1] = y
-	a.buf[a.off+2] = z
-	a.buf[a.off+3] = w
-	a.off += 4
-}
-
-// PutInt16 writes v into the buffer using little-endian encoding.
-func (a *AsmBuf) PutInt16(v int16) {
-	a.buf[a.off+0] = byte(v)
-	a.buf[a.off+1] = byte(v >> 8)
-	a.off += 2
-}
-
-// PutInt32 writes v into the buffer using little-endian encoding.
-func (a *AsmBuf) PutInt32(v int32) {
-	a.buf[a.off+0] = byte(v)
-	a.buf[a.off+1] = byte(v >> 8)
-	a.buf[a.off+2] = byte(v >> 16)
-	a.buf[a.off+3] = byte(v >> 24)
-	a.off += 4
-}
-
-// PutInt64 writes v into the buffer using little-endian encoding.
-func (a *AsmBuf) PutInt64(v int64) {
-	a.buf[a.off+0] = byte(v)
-	a.buf[a.off+1] = byte(v >> 8)
-	a.buf[a.off+2] = byte(v >> 16)
-	a.buf[a.off+3] = byte(v >> 24)
-	a.buf[a.off+4] = byte(v >> 32)
-	a.buf[a.off+5] = byte(v >> 40)
-	a.buf[a.off+6] = byte(v >> 48)
-	a.buf[a.off+7] = byte(v >> 56)
-	a.off += 8
-}
-
-// Put copies b into the buffer.
-func (a *AsmBuf) Put(b []byte) {
-	copy(a.buf[a.off:], b)
-	a.off += len(b)
-}
-
-// Insert inserts b at offset i.
-func (a *AsmBuf) Insert(i int, b byte) {
-	a.off++
-	copy(a.buf[i+1:a.off], a.buf[i:a.off-1])
-	a.buf[i] = b
-}
-
-// Last returns the byte at the end of the buffer.
-func (a *AsmBuf) Last() byte { return a.buf[a.off-1] }
-
-// Len returns the length of the buffer.
-func (a *AsmBuf) Len() int { return a.off }
-
-// Bytes returns the contents of the buffer.
-func (a *AsmBuf) Bytes() []byte { return a.buf[:a.off] }
-
-// Reset empties the buffer.
-func (a *AsmBuf) Reset() { a.off = 0 }
-
-// Peek returns the byte at offset i.
-func (a *AsmBuf) Peek(i int) byte { return a.buf[i] }