feat(lint): flag writes to the platform-reserved register

2026-08-30 21:42:12 +02:00
parent 62f6fb4faf
commit 75bd83fd52
4 changed files with 126 additions and 0 deletions
@@ -436,3 +436,62 @@ TEXT ·f(SB), NOSPLIT, $0
 		t.Fatalf("canonical names must not be flagged: %+v", diags)
 	}
 }
+
+func TestReservedRegisterWrite(t *testing.T) {
+	// A write to R18, the arm64 platform register, is flagged.
+	diags := lintSrcArch(t, "k_arm64.s", `
+#include "textflag.h"
+TEXT ·f(SB), NOSPLIT, $0
+	MOVD $1, R18
+	RET
+`)
+	if codes(diags)[CodeReservedRegister] != 1 {
+		t.Fatalf("want one reserved-register-write, got %+v", diags)
+	}
+
+	// Reading R18 (as a base address) is legitimate.
+	diags = lintSrcArch(t, "k_arm64.s", `
+#include "textflag.h"
+TEXT ·f(SB), NOSPLIT, $0
+	MOVD (R18), R0
+	RET
+`)
+	if codes(diags)[CodeReservedRegister] != 0 {
+		t.Fatalf("reads must not be flagged: %+v", diags)
+	}
+
+	// Other registers are unaffected.
+	diags = lintSrcArch(t, "k_arm64.s", `
+#include "textflag.h"
+TEXT ·f(SB), NOSPLIT, $0
+	MOVD $1, R19
+	RET
+`)
+	if codes(diags)[CodeReservedRegister] != 0 {
+		t.Fatalf("R19 must not be flagged: %+v", diags)
+	}
+
+	// Macro-using files are exempt: an opaque macro may save and restore R18.
+	diags = lintSrcArch(t, "k_arm64.s", `
+#include "textflag.h"
+#define SAVE_R18 MOVD R18, R4
+TEXT ·f(SB), NOSPLIT, $0
+	SAVE_R18
+	MOVD $1, R18
+	RET
+`)
+	if codes(diags)[CodeReservedRegister] != 0 {
+		t.Fatalf("macro-using files must be exempt: %+v", diags)
+	}
+
+	// The rule is arm64-only: an amd64 file has no reserved register.
+	diags = lintSrc(t, `
+#include "textflag.h"
+TEXT ·f(SB), NOSPLIT, $0
+	MOVQ $1, AX
+	RET
+`)
+	if codes(diags)[CodeReservedRegister] != 0 {
+		t.Fatalf("amd64 must not be flagged: %+v", diags)
+	}
+}