first pass at DATA sections

examples/data/asm.go

@@ -0,0 +1,34 @@
+// +build ignore
+
+package main
+
+import (
+	"math"
+
+	. "github.com/mmcloughlin/avo/build"
+	. "github.com/mmcloughlin/avo/operand"
+)
+
+func main() {
+	bytes := GLOBL("bytes")
+	DATA(0, U64(0x0011223344556677))
+	DATA(8, String("strconst"))
+	DATA(16, F32(math.Pi))
+	DATA(24, F64(math.Pi))
+	DATA(32, U32(0x00112233))
+	DATA(36, U16(0x4455))
+	DATA(38, U8(0x66))
+	DATA(39, U8(0x77))
+
+	// TEXT ·DataAt(SB),0,$0-9
+	TEXT("DataAt", "func(i int) byte")
+	i := Load(Param("i"), GP64v()) // MOVQ	i+0(FP), AX
+	ptr := Mem{Base: GP64v()}
+	LEAQ(bytes, ptr.Base) // LEAQ	b<>+0x00(SB), BX
+	b := GP8v()
+	MOVB(ptr.Idx(i, 1), b)   // MOVB	0(BX)(AX*1), CL
+	Store(b, ReturnIndex(0)) // MOVB	CL, ret+8(FP)
+	RET()                    // RET
+
+	Generate()
+}