gasm-sdk/lint/liveness_test.go

// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: BSD-3-Clause

package lint

import "testing"

// TestRegisterClobber checks the register-clobber audit is calibrated to the
// Go ABI (cmd/compile/abi-internal.md), not the platform ABI: Go's
// stack-based ABI0 — which hand-written assembly uses — has no System V
// style callee-saved registers, so argument and scratch registers may be
// clobbered freely.  Only the registers the ABI fixes across calls (the
// frame pointer, the goroutine pointer, OS-reserved registers) are audited.
func TestRegisterClobber(t *testing.T) {
	// amd64: BX, R12, R13 and R15 are argument/permanent-scratch registers in
	// Go ABI0 — writing them unsaved is legal (a System V calibration would
	// report all of these).
	scratch := lintSrc(t, "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tMOVQ CX, BX\n"+
		"\tXORL R12, R12\n"+
		"\tXORL R13, R13\n"+
		"\tXORL R15, R15\n"+
		"\tRET\n")
	if codes(scratch)[CodeRegisterClobber] != 0 {
		t.Fatalf("Go ABI0 scratch registers must not be flagged: %+v", scratch)
	}

	// amd64: R14 (the goroutine pointer) in a NOSPLIT function without calls
	// is the runtime's own pattern — the ABI0 transition restores it — so it
	// is not flagged.
	leaf := lintSrc(t, "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tXORL R14, R14\n"+
		"\tRET\n")
	if codes(leaf)[CodeRegisterClobber] != 0 {
		t.Fatalf("R14 in a NOSPLIT leaf must not be flagged: %+v", leaf)
	}

	// amd64: R14 in a function that makes a call is a genuine hazard.
	withCall := lintSrc(t, "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tXORL R14, R14\n"+
		"\tCALL ·g(SB)\n"+
		"\tRET\n")
	if codes(withCall)[CodeRegisterClobber] != 1 {
		t.Fatalf("unsaved R14 with a call should be flagged: %+v", withCall)
	}

	// amd64: R14 in a non-NOSPLIT function is a hazard regardless of calls.
	split := lintSrc(t, "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), $0\n"+
		"\tMOVQ CX, R14\n"+
		"\tRET\n")
	if codes(split)[CodeRegisterClobber] != 1 {
		t.Fatalf("unsaved R14 in a non-NOSPLIT function should be flagged: %+v", split)
	}

	// amd64: R14 saved and restored around the call is preserved.
	saved := lintSrc(t, "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $8\n"+
		"\tPUSHQ R14\n"+
		"\tXORL R14, R14\n"+
		"\tCALL ·g(SB)\n"+
		"\tPOPQ R14\n"+
		"\tRET\n")
	if codes(saved)[CodeRegisterClobber] != 0 {
		t.Fatalf("saved/restored R14 must not be flagged: %+v", saved)
	}

	// amd64: BP maintains the frame chain and is always audited.
	bp := lintSrc(t, "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tMOVQ CX, BP\n"+
		"\tRET\n")
	if codes(bp)[CodeRegisterClobber] != 1 {
		t.Fatalf("unsaved BP write should be flagged: %+v", bp)
	}

	// arm64: R20 is scratch; R28 (goroutine pointer) and R18 (OS-reserved)
	// are fixed by the Go ABI.
	armScratch := lintSrcArch(t, "t_arm64.s", "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tMOVD R0, R20\n"+
		"\tRET\n")
	if codes(armScratch)[CodeRegisterClobber] != 0 {
		t.Fatalf("arm64 scratch register must not be flagged: %+v", armScratch)
	}
	armG := lintSrcArch(t, "t_arm64.s", "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tMOVD R0, R28\n"+
		"\tRET\n")
	if codes(armG)[CodeRegisterClobber] != 1 {
		t.Fatalf("unsaved arm64 R28 write should be flagged: %+v", armG)
	}
	armReserved := lintSrcArch(t, "t_arm64.s", "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tMOVD R0, R18\n"+
		"\tRET\n")
	if codes(armReserved)[CodeRegisterClobber] != 1 {
		t.Fatalf("arm64 R18 write should be flagged: %+v", armReserved)
	}

	// riscv64: X27 holds the goroutine; X5–X7 are scratch.
	riscScratch := lintSrcArch(t, "t_riscv64.s", "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tMOV X5, X6\n"+
		"\tRET\n")
	if codes(riscScratch)[CodeRegisterClobber] != 0 {
		t.Fatalf("riscv64 scratch register must not be flagged: %+v", riscScratch)
	}
	riscG := lintSrcArch(t, "t_riscv64.s", "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tMOV X5, X27\n"+
		"\tRET\n")
	if codes(riscG)[CodeRegisterClobber] != 1 {
		t.Fatalf("unsaved riscv64 X27 write should be flagged: %+v", riscG)
	}

	// loong64: R22 holds the goroutine; R5–R19 are argument/scratch.
	loongScratch := lintSrcArch(t, "t_loong64.s", "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tMOVV R5, R6\n"+
		"\tRET\n")
	if codes(loongScratch)[CodeRegisterClobber] != 0 {
		t.Fatalf("loong64 scratch register must not be flagged: %+v", loongScratch)
	}
	loongG := lintSrcArch(t, "t_loong64.s", "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tMOVV R5, R22\n"+
		"\tRET\n")
	if codes(loongG)[CodeRegisterClobber] != 1 {
		t.Fatalf("unsaved loong64 R22 write should be flagged: %+v", loongG)
	}
}

// TestFuncdata validates the FUNCDATA/PCDATA structural checks.
func TestFuncdata(t *testing.T) {
	// Well formed: no findings.
	good := lintSrc(t, "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tFUNCDATA $0, gclocals·abc(SB)\n"+
		"\tPCDATA $1, $0\n"+
		"\tRET\n")
	if codes(good)[CodeFuncdata] != 0 {
		t.Fatalf("well-formed FUNCDATA/PCDATA must not be flagged: %+v", good)
	}

	// FUNCDATA with one operand.
	bad1 := lintSrc(t, "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tFUNCDATA $0\n"+
		"\tRET\n")
	if codes(bad1)[CodeFuncdata] == 0 {
		t.Fatal("FUNCDATA with one operand should be flagged")
	}

	// PCDATA with a non-immediate value.
	bad2 := lintSrc(t, "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tPCDATA $0, AX\n"+
		"\tRET\n")
	if codes(bad2)[CodeFuncdata] == 0 {
		t.Fatal("PCDATA with a register value should be flagged")
	}

	// FUNCDATA index out of range.
	bad3 := lintSrc(t, "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tFUNCDATA $99, gclocals·abc(SB)\n"+
		"\tRET\n")
	if codes(bad3)[CodeFuncdata] == 0 {
		t.Fatal("out-of-range FUNCDATA index should be flagged")
	}
}