feat(asm): encode indirect JMP and CALL on all four architectures

Assisted-by: GLM 5.3 Flash

asm/arm64_encode_test.go

@@ -572,3 +572,42 @@ func leWords(b []byte) []uint32 {
 	}
 	return w
 }
+
+// TestArm64IndirectBranch pins the indirect branch forms in a leaf function:
+// JMP (Rn) lowers to BR Rn, matching the toolchain's spelling, and the raw
+// BR/BLR mnemonics encode directly (a gasm superset the toolchain's front
+// end does not accept).  CALL (Rn) shares the BLR path and its non-leaf
+// prologue parity is covered by the ground-truth kernel.
+func TestArm64IndirectBranch(t *testing.T) {
+	src := `#include "textflag.h"
+
+TEXT ·f(SB), NOSPLIT, $0-0
+	JMP (R0)
+	BR R5
+	BLR R6
+	RET
+`
+	f, errs := parser.Parse("test_arm64.s", src)
+	if len(errs) > 0 {
+		t.Fatalf("parse: %v", errs)
+	}
+	img, err := AssembleFileARM64(f)
+	if err != nil {
+		t.Fatalf("AssembleFileARM64: %v", err)
+	}
+	want := []uint32{
+		0xd61f0000, // BR R0
+		0xd61f00a0, // BR R5
+		0xd63f00c0, // BLR R6
+		0xd65f03c0, // RET (BR LR)
+	}
+	got := leWords(img.Code)
+	if len(got) != len(want) {
+		t.Fatalf("word count = %d, want %d", len(got), len(want))
+	}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Errorf("word %d = %08x, want %08x", i, got[i], want[i])
+		}
+	}
+}