arch/arm64/kernel/boot.S


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/* SPDX-License-Identifier: GPL-2.0+ */
/*
 * boot.S - the final jump to the payload. x0 = dtb, x1 = x2 = x3 = 0,
 * MMU and caches off, D cache flushed, I cache invalidated. that is
 * the whole contract from Documentation/arch/arm64/booting.rst.
 *
 * Copyright (C) 2026 Bradley Morgan <brads@mainlining.org>
 */

#include <asm/linkage.h>

.pushsection .text.tb_boot_linux, "ax"
ENTRY(tb_boot_linux)
	/* ep in x0, dtb in x1, per the kernel boot protocol */
	mov	x8, x0
	mov	x0, x1
	mov	x1, xzr
	mov	x2, xzr
	mov	x3, xzr

	/* clean the caches so the kernel reads the image from RAM */
	bl	tb_flush_dcache_all
	bl	tb_invalidate_icache_all

	/* MMU off, caches off, the kernel sets up its own state */
	mrs	x9, sctlr_el1
	bic	x9, x9, #(1 << 0)	/* M, MMU */
	bic	x9, x9, #(1 << 2)	/* C, D-cache */
	bic	x9, x9, #(1 << 12)	/* I, I-cache */
	msr	sctlr_el1, x9
	isb

	br	x8
ENDPROC(tb_boot_linux)
.popsection