U-Boot

// SPDX-License-Identifier: GPL-2.0+
/*
 * Hello world EFI application
 *
 * Copyright 2020, Heinrich Schuchardt <xypron.glpk@gmx.de>
 *
 * This test program is used to test the invocation of an EFI application.
 * It writes
 *
 * * a greeting
 * * the firmware's UEFI version
 * * the installed configuration tables
 * * the boot device's device path and the file path
 *
 * to the console.
 */

#include <efi_api.h>

static const efi_guid_t loaded_image_guid = EFI_LOADED_IMAGE_PROTOCOL_GUID;
static const efi_guid_t device_path_to_text_protocol_guid =
	EFI_DEVICE_PATH_TO_TEXT_PROTOCOL_GUID;
static const efi_guid_t device_path_guid = EFI_DEVICE_PATH_PROTOCOL_GUID;
static const efi_guid_t fdt_guid = EFI_FDT_GUID;
static const efi_guid_t acpi_guid = EFI_ACPI_TABLE_GUID;
static const efi_guid_t smbios_guid = SMBIOS_TABLE_GUID;

static struct efi_system_table *systable;
static struct efi_boot_services *boottime;
static struct efi_simple_text_output_protocol *con_out;

/**
 * print_uefi_revision() - print UEFI revision number
 */
static void print_uefi_revision(void)
{
	u16 rev[] = L"0.0.0";

	rev[0] = (systable->hdr.revision >> 16) + '0';
	rev[4] = systable->hdr.revision & 0xffff;
	for (; rev[4] >= 10;) {
		rev[4] -= 10;
		++rev[2];
	}
	/* Third digit is only to be shown if non-zero */
	if (rev[4])
		rev[4] += '0';
	else
		rev[3] = 0;

	con_out->output_string(con_out, L"Running on UEFI ");
	con_out->output_string(con_out, rev);
	con_out->output_string(con_out, L"\r\n");
}

/**
 * print_config_tables() - print configuration tables
 */
static void print_config_tables(void)
{
	efi_uintn_t i;

	/* Find configuration tables */
	for (i = 0; i < systable->nr_tables; ++i) {
		if (!memcmp(&systable->tables[i].guid, &fdt_guid,
			    sizeof(efi_guid_t)))
			con_out->output_string
					(con_out, L"Have device tree\r\n");
		if (!memcmp(&systable->tables[i].guid, &acpi_guid,
			    sizeof(efi_guid_t)))
			con_out->output_string
					(con_out, L"Have ACPI 2.0 table\r\n");
		if (!memcmp(&systable->tables[i].guid, &smbios_guid,
			    sizeof(efi_guid_t)))
			con_out->output_string
					(con_out, L"Have SMBIOS table\r\n");
	}
}

/**
 * print_load_options() - print load options
 *
 * @systable:	system table
 * @con_out:	simple text output protocol
 */
void print_load_options(struct efi_loaded_image *loaded_image)
{
	/* Output the load options */
	con_out->output_string(con_out, L"Load options: ");
	if (loaded_image->load_options_size && loaded_image->load_options)
		con_out->output_string(con_out,
				       (u16 *)loaded_image->load_options);
	else
		con_out->output_string(con_out, L"<none>");
	con_out->output_string(con_out, L"\r\n");
}

/**
 * print_device_path() - print device path
 *
 * @device_path:	device path to print
 * @dp2txt:		device path to text protocol
 */
efi_status_t print_device_path(struct efi_device_path *device_path,
			       struct efi_device_path_to_text_protocol *dp2txt)
{
	u16 *string;
	efi_status_t ret;

	if (!device_path) {
		con_out->output_string(con_out, L"<none>\r\n");
		return EFI_SUCCESS;
	}

	string = dp2txt->convert_device_path_to_text(device_path, true, false);
	if (!string) {
		con_out->output_string
			(con_out, L"Cannot convert device path to text\r\n");
		return EFI_OUT_OF_RESOURCES;
	}
	con_out->output_string(con_out, string);
	con_out->output_string(con_out, L"\r\n");
	ret = boottime->free_pool(string);
	if (ret != EFI_SUCCESS) {
		con_out->output_string(con_out, L"Cannot free pool memory\r\n");
		return ret;
	}
	return EFI_SUCCESS;
}

/**
 * efi_main() - entry point of the EFI application.
 *
 * @handle:	handle of the loaded image
 * @systab:	system table
 * @return:	status code
 */
efi_status_t EFIAPI efi_main(efi_handle_t handle,
			     struct efi_system_table *systab)
{
	struct efi_loaded_image *loaded_image;
	struct efi_device_path_to_text_protocol *device_path_to_text;
	struct efi_device_path *device_path;
	efi_status_t ret;

	systable = systab;
	boottime = systable->boottime;
	con_out = systable->con_out;

	/* UEFI requires CR LF */
	con_out->output_string(con_out, L"Hello, world!\r\n");

	print_uefi_revision();
	print_config_tables();

	/* Get the loaded image protocol */
	ret = boottime->handle_protocol(handle, &loaded_image_guid,
					(void **)&loaded_image);
	if (ret != EFI_SUCCESS) {
		con_out->output_string
			(con_out, L"Cannot open loaded image protocol\r\n");
		goto out;
	}
	print_load_options(loaded_image);

	/* Get the device path to text protocol */
	ret = boottime->locate_protocol(&device_path_to_text_protocol_guid,
					NULL, (void **)&device_path_to_text);
	if (ret != EFI_SUCCESS) {
		con_out->output_string
			(con_out, L"Cannot open device path to text protocol\r\n");
		goto out;
	}
	if (!loaded_image->device_handle) {
		con_out->output_string
			(con_out, L"Missing device handle\r\n");
		goto out;
	}
	ret = boottime->handle_protocol(loaded_image->device_handle,
					&device_path_guid,
					(void **)&device_path);
	if (ret != EFI_SUCCESS) {
		con_out->output_string
			(con_out, L"Missing device path for device handle\r\n");
		goto out;
	}
	con_out->output_string(con_out, L"Boot device: ");
	ret = print_device_path(device_path, device_path_to_text);
	if (ret != EFI_SUCCESS)
		goto out;
	con_out->output_string(con_out, L"File path: ");
	ret = print_device_path(loaded_image->file_path, device_path_to_text);
	if (ret != EFI_SUCCESS)
		goto out;

out:
	boottime->exit(handle, ret, 0, NULL);

	/* We should never arrive here */
	return ret;
}