feat(asm): emit the arm64 stack-split guard and morestack block

asm/arm64_reloc_test.go

@@ -27,6 +27,8 @@ func parseArm64File(t *testing.T, src string) *Image {
 // TestArm64RelocOffsetsIncludePrologue pins the function-relative relocation
 // offsets of a framed function: the offsets used to exclude the prologue, so
 // every relocation landed on a prologue instruction in the GOOBJ/ELF output.
+// The function calls an external, so it is a non-leaf and carries the
+// stack-split guard (12 bytes, small class) before the prologue.
 func TestArm64RelocOffsetsIncludePrologue(t *testing.T) {
 	img := parseArm64File(t, "TEXT \u00b7f(SB), $16-0\n"+
 		"\tBL ext\u00b7foo(SB)\n"+
@@ -36,8 +38,8 @@ func TestArm64RelocOffsetsIncludePrologue(t *testing.T) {
 		"GLOBL gdata(SB), $8\n")
 	fn := img.Funcs[0]
 
-	// Layout: 12-byte prologue, BL (12), ADRP+ADD (16, 20), ADRP+ADD (24, 28),
-	// 12-byte epilogue with RET.
+	// Layout: 12-byte guard, 12-byte prologue, BL (24), ADRP+ADD (28, 32),
+	// ADRP+ADD (36, 40), 12-byte epilogue with RET, 12-byte morestack block.
 	want := []struct {
 		off      int
 		after    int
@@ -45,11 +47,12 @@ func TestArm64RelocOffsetsIncludePrologue(t *testing.T) {
 		kind     RelocKind
 		external bool
 	}{
-		{12, 16, "foo", RelArm64Branch, true},
-		{16, 16, "gdata", RelArm64Addr, false},
-		{20, 20, "gdata", RelArm64Addr, false},
-		{24, 24, "extsym", RelArm64Addr, true},
-		{28, 28, "extsym", RelArm64Addr, true},
+		{24, 28, "foo", RelArm64Branch, true},
+		{28, 28, "gdata", RelArm64Addr, false},
+		{32, 32, "gdata", RelArm64Addr, false},
+		{36, 36, "extsym", RelArm64Addr, true},
+		{40, 40, "extsym", RelArm64Addr, true},
+		{60, 64, "runtime\u00b7morestack_noctxt", RelArm64Branch, true},
 	}
 	if len(fn.Relocs) != len(want) {
 		t.Fatalf("relocs = %d, want %d", len(fn.Relocs), len(want))
@@ -64,7 +67,7 @@ func TestArm64RelocOffsetsIncludePrologue(t *testing.T) {
 
 	// The BL with a zero offset sits exactly at the first reloc site.
 	code := img.Code[fn.Offset : fn.Offset+fn.Size]
-	if w := binary.LittleEndian.Uint32(code[12:16]); w != 0x94000000 {
+	if w := binary.LittleEndian.Uint32(code[24:28]); w != 0x94000000 {
 		t.Errorf("BL word = %08x, want 94000000", w)
 	}
 }