cregit-Linux how code gets into the kernel

Release 4.7 drivers/tty/serial/earlycon-arm-semihost.c

/*
 * Copyright (C) 2012 ARM Ltd.
 * Author: Marc Zyngier <marc.zyngier@arm.com>
 *
 * Adapted for ARM and earlycon:
 * Copyright (C) 2014 Linaro Ltd.
 * Author: Rob Herring <robh@kernel.org>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#include <linux/kernel.h>
#include <linux/console.h>
#include <linux/init.h>
#include <linux/serial_core.h>

#ifdef CONFIG_THUMB2_KERNEL

#define SEMIHOST_SWI	"0xab"
#else

#define SEMIHOST_SWI	"0x123456"
#endif

/*
 * Semihosting-based debug console
 */

static void smh_putc(struct uart_port *port, int c) { #ifdef CONFIG_ARM64 asm volatile("mov x1, %0\n" "mov x0, #3\n" "hlt 0xf000\n" : : "r" (&c) : "x0", "x1", "memory"); #else asm volatile("mov r1, %0\n" "mov r0, #3\n" "svc " SEMIHOST_SWI "\n" : : "r" (&c) : "r0", "r1", "memory"); #endif }

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static void smh_write(struct console *con, const char *s, unsigned n) { struct earlycon_device *dev = con->data; uart_console_write(&dev->port, s, n, smh_putc); }

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int __init early_smh_setup(struct earlycon_device *device, const char *opt) { device->con->write = smh_write; return 0; }

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EARLYCON_DECLARE(smh, early_smh_setup);

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