feat(asm): emit the riscv64 stack-split guard and fix large-frame addressing

asm/guard_test.go

@@ -143,3 +143,45 @@ func TestStackGuardBytesARM64(t *testing.T) {
 		}
 	}
 }
+
+// The riscv64 stack-split guard, pinned from `go tool asm` (Go 1.27,
+// riscv64): the morestack call sits between the guard and the body, and the
+// guard branches forward over it.  Relocation fields are masked.
+func TestStackGuardBytesRISCV64(t *testing.T) {
+	for _, tt := range []struct {
+		name string
+		src  string
+		want string
+	}{
+		{"leafsmall", "TEXT \u00b7leafsmall(SB), $16-0\n\tRET\n",
+			"03b30d0163662300000000006ff05fff233411fe211106e08260610167800000"},
+		{"leafmed", "TEXT \u00b7leafmed(SB), $256-0\n\tRET\n",
+			"03b30d01930381f763667300000000006ff01fff233c11ee130181ef06e082601301811067800000"},
+		{"leafbig", "TEXT \u00b7leafbig(SB), $8192-0\n\tRET\n",
+			"03b30d0189639b8383f863697100f97f9b8f8f07b303f10163667300000000006ff01ffef97f8a9f23bc1ffef97fe13f7e9106e08260896fa12f7e9167800000"},
+		{"frameless", "TEXT \u00b7frameless(SB), $0-0\n\tCALL \u00b7other(SB)\n\tRET\nTEXT \u00b7other(SB), NOSPLIT, $0\n\tRET\n",
+			"03b30d0163662300000000006ff05fff233c11fe611106e0000000008260210167800000"},
+		{"nosplit", "TEXT \u00b7nosplit(SB), NOSPLIT, $16-0\n\tRET\n",
+			"233411fe211106e08260610167800000"},
+	} {
+		f, errs := parser.Parse("g_riscv64.s", tt.src)
+		if len(errs) > 0 {
+			t.Fatalf("%s: parse: %v", tt.name, errs)
+		}
+		img, err := AssembleFileRISCV(f)
+		if err != nil {
+			t.Fatalf("%s: assemble: %v", tt.name, err)
+		}
+		fn := img.Funcs[0]
+		code := append([]byte(nil), img.Code[fn.Offset:fn.Offset+fn.Size]...)
+		for _, r := range fn.Relocs {
+			for j := r.Off; j < r.Off+4 && j < len(code); j++ {
+				code[j] = 0
+			}
+		}
+		got := hex.EncodeToString(code)
+		if got != tt.want {
+			t.Errorf("%s:\n  got  %s\n  want %s", tt.name, got, tt.want)
+		}
+	}
+}