common/main.c


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/*
 * main.c - the C entry. console up first, then the board from the dtb,
 * then find a payload and jump. called from start.S with x0 = dtb.
 *
 * Copyright (c) 2026 Bradley Morgan <brads@mainlining.org>
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files
 * (the "Software"), to deal in the Software without restriction,
 * including without limitation the rights to use, copy, modify, merge,
 * publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#include <string.h>
#include <stdio.h>
#include <sys/types.h>
#include <stdint.h>
#include <libfdt.h>
#include <debug.h>
#include <semihosting.h>
#include <boot.h>

#define TB_VERSION "0.1"

extern int tb_console_init(const void *dtb);
extern void __NO_RETURN tb_boot_linux(uintptr_t ep, const void *dtb);

/*
 * staging area for the payload. past the bootloader at the bottom of
 * RAM, the image header decides its final resting place.
 */
#define TB_LOAD_ADDR	0x40200000

static int tb_read_memory(const void *dtb, uintptr_t *base, uint32 *size)
{
	const fdt32_t *prop;
	int len;
	int node;

	node = fdt_path_offset(dtb, "/memory@40000000");
	if (node < 0)
		node = fdt_path_offset(dtb, "/memory");
	if (node < 0)
		return -1;

	prop = fdt_getprop(dtb, node, "reg", &len);
	if (!prop || len < 12)
		return -1;

	*base = ((uintptr_t)fdt32_to_cpu(prop[0]) << 32) |
		fdt32_to_cpu(prop[1]);
	*size = fdt32_to_cpu(prop[2]);
	return 0;
}

/*
 * bootargs from chosen. passed straight through, tashaboot does not
 * rewrite the kernel command line.
 */
static const char *tb_get_cmdline(const void *dtb)
{
	const char *cmdline;
	int len;
	int node;

	node = fdt_path_offset(dtb, "/chosen");
	if (node < 0)
		return NULL;

	cmdline = fdt_getprop(dtb, node, "bootargs", &len);
	if (!cmdline || len <= 0)
		return NULL;
	return cmdline;
}

/*
 * tashaboot,bootfile in chosen overrides the default image name. the
 * host file that semihosting serves is what gets loaded.
 */
static const char *tb_get_bootfile(const void *dtb)
{
	const char *bootfile;
	int len;
	int node;

	node = fdt_path_offset(dtb, "/chosen");
	if (node < 0)
		return NULL;

	bootfile = fdt_getprop(dtb, node, "tashaboot,bootfile", &len);
	if (!bootfile || len <= 0)
		return NULL;
	return bootfile;
}

void tashaboot_main(const void *dtb)
{
	struct tb_image img;
	uintptr_t mem_base = 0;
	uint32 mem_size = 0;
	const char *cmdline;
	const char *bootfile;
	int ret;

	if (tb_console_init(dtb))
		return;

	dprintf(ALWAYS, "tashaboot " TB_VERSION "\n");
	dprintf(ALWAYS, "dtb at %p\n", dtb);

	if (fdt_check_header(dtb)) {
		dprintf(ALWAYS, "bad dtb header, halting\n");
		platform_halt();
	}

	if (tb_read_memory(dtb, &mem_base, &mem_size)) {
		dprintf(ALWAYS, "no usable memory node, halting\n");
		platform_halt();
	}
	dprintf(ALWAYS, "memory %lx-%lx\n", mem_base, mem_base + mem_size);

	cmdline = tb_get_cmdline(dtb);
	if (cmdline)
		dprintf(ALWAYS, "cmdline: %s\n", cmdline);

	/*
	 * semihosting first, it is the qemu development path. a real board
	 * boots from flash or block storage, those loaders come later and
	 * slot in right here.
	 */
	if (!smh_probe()) {
		dprintf(ALWAYS, "no semihosting host, halting\n");
		platform_halt();
	}

	bootfile = tb_get_bootfile(dtb);
	if (!bootfile)
		bootfile = "Image";

	ret = tb_load_semihosting(bootfile, TB_LOAD_ADDR, mem_base, mem_size, &img);
	if (ret) {
		dprintf(ALWAYS, "load failed (%d), halting\n", ret);
		platform_halt();
	}

	dprintf(ALWAYS, "loaded %llu bytes at %lx, entry %lx\n",
		(unsigned long long)img.size, img.load, img.ep);
	dprintf(ALWAYS, "jumping\n");

	tb_boot_linux(img.ep, dtb);
}