asm: Add LoadMemSX instruction

ISAv4 adds a new instruction to load a memory value and sign extend it.
To do so a new mode is used. This commit adds a new function to emit
this instruction and adds the logic to print it nicely.

Signed-off-by: Dylan Reimerink <[email protected]>

asm/instruction.go

@@ -308,7 +308,7 @@ func (ins Instruction) Format(f fmt.State, c rune) {
 			fmt.Fprintf(f, "imm: %d", ins.Constant)
 		case IndMode:
 			fmt.Fprintf(f, "dst: %s src: %s imm: %d", ins.Dst, ins.Src, ins.Constant)
-		case MemMode:
+		case MemMode, MemSXMode:
 			fmt.Fprintf(f, "dst: %s src: %s off: %d imm: %d", ins.Dst, ins.Src, ins.Offset, ins.Constant)
 		case XAddMode:
 			fmt.Fprintf(f, "dst: %s src: %s", ins.Dst, ins.Src)

asm/load_store.go

@@ -24,6 +24,8 @@ const (
 	IndMode Mode = 0x40
 	// MemMode - load from memory
 	MemMode Mode = 0x60
+	// MemSXMode - load from memory, sign extension
+	MemSXMode Mode = 0x80
 	// XAddMode - add atomically across processors.
 	XAddMode Mode = 0xc0
 )
@@ -73,6 +75,11 @@ func LoadMemOp(size Size) OpCode {
 	return OpCode(LdXClass).SetMode(MemMode).SetSize(size)
 }
 
+// LoadSXMemOp returns the OpCode to load a value of given size from memory sign extended.
+func LoadSXMemOp(size Size) OpCode {
+	return OpCode(LdXClass).SetMode(MemSXMode).SetSize(size)
+}
+
 // LoadMem emits `dst = *(size *)(src + offset)`.
 func LoadMem(dst, src Register, offset int16, size Size) Instruction {
 	return Instruction{
@@ -83,6 +90,20 @@ func LoadMem(dst, src Register, offset int16, size Size) Instruction {
 	}
 }
 
+// LoadMemSX emits `dst = *(size *)(src + offset)` but sign extends dst.
+func LoadMemSX(dst, src Register, offset int16, size Size) Instruction {
+	if size == DWord {
+		return Instruction{OpCode: InvalidOpCode}
+	}
+
+	return Instruction{
+		OpCode: LoadSXMemOp(size),
+		Dst:    dst,
+		Src:    src,
+		Offset: offset,
+	}
+}
+
 // LoadImmOp returns the OpCode to load an immediate of given size.
 //
 // As of kernel 4.20, only DWord size is accepted.