Commit 476476e7 authored by Simon Glass's avatar Simon Glass

efi: Add support for loading U-Boot through an EFI stub

It is useful to be able to load U-Boot onto a board even if is it already
running EFI. This can allow access to the U-Boot command interface, flexible
booting options and easier development.

The easiest way to do this is to build U-Boot as a binary blob and have an
EFI stub copy it into RAM. Add support for this feature, targeting 32-bit

Also add a way to detect when U-Boot has been loaded via a stub. This goes
in common.h since it needs to be widely available so that we avoid redoing
initialisation that should be skipped.
Signed-off-by: default avatarSimon Glass <>
Improvements to how the payload is built:
Signed-off-by: default avatarBin Meng <>
Reviewed-by: default avatarBin Meng <>
Tested-by: default avatarBin Meng <>
parent 465a67cf
......@@ -755,6 +755,7 @@ ALL-$(CONFIG_SPL) += $(CONFIG_SPL_TARGET:"%"=%)
ALL-$(CONFIG_REMAKE_ELF) += u-boot.elf
ALL-$(CONFIG_EFI_APP) += u-boot-app.efi
ALL-$(CONFIG_EFI_STUB) += u-boot-payload.efi
ifneq ($(BUILD_ROM),)
ALL-$(CONFIG_X86_RESET_VECTOR) += u-boot.rom
......@@ -790,6 +791,9 @@ cmd_objcopy = $(OBJCOPY) --gap-fill=0xff $(OBJCOPYFLAGS) \
quiet_cmd_zobjcopy = OBJCOPY $@
cmd_zobjcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@
quiet_cmd_efipayload = OBJCOPY $@
cmd_efipayload = $(OBJCOPY) -I binary -O $(EFIPAYLOAD_BFDTARGET) -B $(EFIPAYLOAD_BFDARCH) $< $@
quiet_cmd_mkimage = MKIMAGE $@
cmd_mkimage = $(objtree)/tools/mkimage $(MKIMAGEFLAGS_$(@F)) -d $< $@ \
$(if $(KBUILD_VERBOSE:1=), >/dev/null)
......@@ -1087,6 +1091,26 @@ OBJCOPYFLAGS_u-boot-app.efi := $(OBJCOPYFLAGS_EFI)
u-boot-app.efi: u-boot FORCE
$(call if_changed,zobjcopy)
u-boot-dtb.bin.o: u-boot-dtb.bin FORCE
$(call if_changed,efipayload) $(LDSCRIPT_EFI) FORCE
$(call if_changed_dep,cpp_lds)
# Rule to link the EFI payload which contains a stub and a U-Boot binary
quiet_cmd_u-boot_payload ?= LD $@
cmd_u-boot_payload ?= $(LD) $(LDFLAGS_EFI_PAYLOAD) -o $@ \
-T \
lib/efi/efi.o lib/efi/efi_stub.o u-boot-dtb.bin.o \
$(addprefix arch/$(ARCH)/lib/efi/,$(EFISTUB))
u-boot-payload: u-boot-dtb.bin.o FORCE
$(call if_changed,u-boot_payload)
OBJCOPYFLAGS_u-boot-payload.efi := $(OBJCOPYFLAGS_EFI)
u-boot-payload.efi: u-boot-payload FORCE
$(call if_changed,zobjcopy)
u-boot-img.bin: spl/u-boot-spl.bin u-boot.img FORCE
$(call if_changed,cat)
......@@ -24,6 +24,10 @@ PLATFORM_LDFLAGS += -Bsymbolic -Bsymbolic-functions -m elf_i386
LDFLAGS_FINAL += --wrap=__divdi3 --wrap=__udivdi3
LDFLAGS_FINAL += --wrap=__moddi3 --wrap=__umoddi3
# This is used in the top-level Makefile which does not include
LDFLAGS_EFI_PAYLOAD := -Bsymbolic -Bsymbolic-functions -shared --no-undefined
OBJCOPYFLAGS_EFI := -j .text -j .sdata -j .data -j .dynamic -j .dynsym \
-j .rel -j .rela -j .reloc
......@@ -31,6 +35,9 @@ CFLAGS_NON_EFI := -mregparm=3
CFLAGS_EFI := -fpic -fshort-wchar
EFIARCH = ia32
LDSCRIPT_EFI := $(srctree)/$(CPUDIR)/efi/elf_$(EFIARCH)
OBJCOPYFLAGS_EFI += --target=efi-app-$(EFIARCH)
......@@ -1021,6 +1021,13 @@ int cpu_release(int nr, int argc, char * const argv[]);
offsetof(struct structure, member) == offset, \
"`struct " #structure "` offset for `" #member "` is not " #offset)
/* Avoid using CONFIG_EFI_STUB directly as we may boot from other loaders */
#define ll_boot_init() false
#define ll_boot_init() true
/* Pull in stuff for the build system */
# include <environment.h>
......@@ -268,11 +268,15 @@ struct efi_priv {
/* Base address of the EFI image */
extern char image_base[];
/* Start and end of U-Boot image (for payload) */
extern char _binary_u_boot_dtb_bin_start[], _binary_u_boot_dtb_bin_end[];
* efi_get_sys_table() - Get access to the main EFI system table
* @return pointer to EFI system table
struct efi_system_table *efi_get_sys_table(void);
......@@ -20,6 +20,11 @@ config EFI_APP
command prompt and memory and I/O functions. Use 'reset' to return
to EFI.
config EFI_STUB
bool "Support running as an EFI payload"
hex "Amount of EFI RAM for U-Boot"
depends on EFI_APP
......@@ -30,4 +35,20 @@ config EFI_RAM_SIZE
other smaller amounts) and it can never be increased after that.
It is used as the RAM size in with U-Boot.
prompt "EFI 32/64-bit selection"
depends on EFI_STUB
EFI does not support mixing 32-bit and 64-bit modes. This is a
significant problem because it means that you must build a stub with
the correct type for EFI to load it correctly. If you are using
32-bit EFI, select 32-bit here, else select 64-bit. Failure to do
this may produce no error message - it just won't start!
config EFI_STUB_32BIT
bool "Produce a stub for running with 32-bit EFI"
config EFI_STUB_64BIT
bool "Produce a stub for running with 64-bit EFI"
......@@ -5,3 +5,12 @@
obj-$(CONFIG_EFI_APP) += efi_app.o efi.o
CFLAGS_REMOVE_efi_stub.o := -mregparm=3 \
$(if $(CONFIG_EFI_STUB_64BIT),-march=i386 -m32)
CFLAGS_efi_stub.o := -fpic -fshort-wchar
CFLAGS_REMOVE_efi.o := -mregparm=3 \
$(if $(CONFIG_EFI_STUB_64BIT),-march=i386 -m32)
CFLAGS_efi.o := -fpic -fshort-wchar
extra-$(CONFIG_EFI_STUB) += efi_stub.o efi.o
* Copyright (c) 2015 Google, Inc
* SPDX-License-Identifier: GPL-2.0+
* EFI information obtained here:
* Loads a payload (U-Boot) within the EFI environment. This is built as a
* 32-bit EFI application.
#include <common.h>
#include <debug_uart.h>
#include <efi.h>
#include <efi_api.h>
#include <errno.h>
#include <ns16550.h>
#include <asm/cpu.h>
#include <asm/io.h>
#include <linux/err.h>
#include <linux/types.h>
#ifndef CONFIG_X86
* Problem areas:
* - putc() uses the ns16550 address directly and assumed I/O access. Many
* platforms will use memory access
* get_codeseg32() is only meaningful on x86
#error "This file needs to be ported for use on architectures"
static struct efi_priv *global_priv;
static bool use_uart;
struct __packed desctab_info {
uint16_t limit;
uint64_t addr;
uint16_t pad;
* EFI uses Unicode and we don't. The easiest way to get a sensible output
* function is to use the U-Boot debug UART. We use EFI's console output
* function where available, and assume the built-in UART after that. We rely
* on EFI to set up the UART for us and just bring in the functions here.
* This last bit is a bit icky, but it's only for debugging anyway. We could
* build in ns16550.c with some effort, but this is a payload loader after
* all.
* Note: We avoid using printf() so we don't need to bring in lib/vsprintf.c.
* That would require some refactoring since we already build this for U-Boot.
* Building an EFI shared library version would have to be a separate stem.
* That might push us to using the SPL framework to build this stub. However
* that would involve a round of EFI-specific changes in SPL. Worth
* considering if we start needing more U-Boot functionality. Note that we
* could then move get_codeseg32() to arch/x86/cpu/cpu.c.
void debug_uart_init(void)
void putc(const char ch)
if (use_uart) {
NS16550_t com_port = (NS16550_t)0x3f8;
while ((inb((ulong)&com_port->lsr) & UART_LSR_THRE) == 0)
outb(ch, (ulong)&com_port->thr);
} else {
efi_putc(global_priv, ch);
if (ch == '\n')
void puts(const char *str)
while (*str)
static void _debug_uart_putc(int ch)
void *memcpy(void *dest, const void *src, size_t size)
unsigned char *dptr = dest;
const unsigned char *ptr = src;
const unsigned char *end = src + size;
while (ptr < end)
*dptr++ = *ptr++;
return dest;
void *memset(void *inptr, int ch, size_t size)
char *ptr = inptr;
char *end = ptr + size;
while (ptr < end)
*ptr++ = ch;
return ptr;
static void jump_to_uboot(ulong cs32, ulong addr, ulong info)
* U-Boot requires these parameters in registers, not on the stack.
* See _x86boot_start() for this code.
typedef void (*func_t)(int bist, int unused, ulong info)
((func_t)addr)(0, 0, info);
/* TODO: Implement this */
static void get_gdt(struct desctab_info *info)
asm volatile ("sgdt %0" : : "m"(*info) : "memory");
static inline unsigned long read_cr3(void)
unsigned long val;
asm volatile("mov %%cr3,%0" : "=r" (val) : : "memory");
return val;
* get_codeseg32() - Find the code segment to use for 32-bit code
* U-Boot only works in 32-bit mode at present, so when booting from 64-bit
* EFI we must first change to 32-bit mode. To do this we need to find the
* correct code segment to use (an entry in the Global Descriptor Table).
* @return code segment GDT offset, or 0 for 32-bit EFI, -ENOENT if not found
static int get_codeseg32(void)
int cs32 = 0;
/* TODO(sjg): Implement this for 64-bit mode */
return cs32;
static int setup_info_table(struct efi_priv *priv, int size)
struct efi_info_hdr *info;
efi_status_t ret;
/* Get some memory for our info table */
priv->info_size = size;
info = efi_malloc(priv, priv->info_size, &ret);
if (ret) {
puts(" No memory for info table: ");
return ret;
memset(info, '\0', sizeof(*info));
info->version = EFI_TABLE_VERSION;
info->hdr_size = sizeof(*info);
priv->info = info;
priv->next_hdr = (char *)info + info->hdr_size;
return 0;
static void add_entry_addr(struct efi_priv *priv, enum efi_entry_t type,
void *ptr1, int size1, void *ptr2, int size2)
struct efi_entry_hdr *hdr = priv->next_hdr;
hdr->type = type;
hdr->size = size1 + size2;
hdr->addr = 0;
hdr->link = ALIGN(sizeof(*hdr) + hdr->size, 16);
priv->next_hdr += hdr->link;
memcpy(hdr + 1, ptr1, size1);
memcpy((void *)(hdr + 1) + size1, ptr2, size2);
priv->info->total_size = (ulong)priv->next_hdr - (ulong)priv->info;
* efi_main() - Start an EFI image
* This function is called by our EFI start-up code. It handles running
* U-Boot. If it returns, EFI will continue.
efi_status_t efi_main(efi_handle_t image, struct efi_system_table *sys_table)
struct efi_priv local_priv, *priv = &local_priv;
struct efi_boot_services *boot = sys_table->boottime;
struct efi_mem_desc *desc;
struct efi_entry_memmap map;
ulong key, desc_size, size;
efi_status_t ret;
u32 version;
int cs32;
ret = efi_init(priv, "Payload", image, sys_table);
if (ret) {
printhex2(ret); puts(" efi_init() failed\n");
return ret;
global_priv = priv;
cs32 = get_codeseg32();
if (cs32 < 0)
/* Get the memory map so we can switch off EFI */
size = 0;
ret = boot->get_memory_map(&size, NULL, &key, &desc_size, &version);
if (ret != EFI_BUFFER_TOO_SMALL) {
puts(" No memory map\n");
return ret;
size += 1024; /* Since doing a malloc() may change the memory map! */
desc = efi_malloc(priv, size, &ret);
if (!desc) {
puts(" No memory for memory descriptor: ");
return ret;
ret = setup_info_table(priv, size + 128);
if (ret)
return ret;
ret = boot->get_memory_map(&size, desc, &key, &desc_size, &version);
if (ret) {
puts(" Can't get memory map\n");
return ret;
ret = boot->exit_boot_services(image, key);
if (ret) {
* Unfortunately it happens that we cannot exit boot services
* the first time. But the second time it work. I don't know
* why but this seems to be a repeatable problem. To get
* around it, just try again.
puts(" Can't exit boot services\n");
size = sizeof(desc);
ret = boot->get_memory_map(&size, desc, &key, &desc_size,
if (ret) {
puts(" Can't get memory map\n");
return ret;
ret = boot->exit_boot_services(image, key);
if (ret) {
puts(" Can't exit boot services 2\n");
return ret;
map.version = version;
map.desc_size = desc_size;
add_entry_addr(priv, EFIET_MEMORY_MAP, &map, sizeof(map), desc, size);
add_entry_addr(priv, EFIET_END, NULL, 0, 0, 0);
/* The EFI UART won't work now, switch to a debug one */
use_uart = true;
memcpy((void *)CONFIG_SYS_TEXT_BASE, _binary_u_boot_dtb_bin_start,
(ulong)_binary_u_boot_dtb_bin_end -
#ifdef DEBUG
puts("EFI table at ");
puts(" size ");
jump_to_uboot(cs32, CONFIG_SYS_TEXT_BASE, (ulong)priv->info);
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