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
initially.

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: Simon Glass <sjg@chromium.org>
Improvements to how the payload is built:
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>

Makefile

@@ -755,6 +755,7 @@ ALL-$(CONFIG_SPL) += $(CONFIG_SPL_TARGET:"%"=%)
 endif
 ALL-$(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)
+
+u-boot-payload.lds: $(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 u-boot-payload.lds \
+      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 u-boot-payload.lds 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)
 

arch/x86/config.mk

@@ -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
+# PLATFORM_LDFLAGS
+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
+EFIPAYLOAD_BFDTARGET = elf32-i386
+
+EFIPAYLOAD_BFDARCH = i386
 
 LDSCRIPT_EFI := $(srctree)/$(CPUDIR)/efi/elf_$(EFIARCH)_efi.lds
 OBJCOPYFLAGS_EFI += --target=efi-app-$(EFIARCH)

include/common.h

@@ -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 */
+#ifdef CONFIG_EFI_STUB
+#define ll_boot_init()	false
+#else
+#define ll_boot_init()	true
+#endif
+
 /* Pull in stuff for the build system */
 #ifdef DO_DEPS_ONLY
 # include <environment.h>

include/efi.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);
 
 /**

lib/efi/Kconfig

@@ -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"
+
+endchoice
+
 config EFI_RAM_SIZE
 	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.
 
+choice
+	prompt "EFI 32/64-bit selection"
+	depends on EFI_STUB
+	help
+	  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"
+
 endchoice

lib/efi/Makefile

@@ -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

lib/efi/efi_stub.c

@@ -0,0 +1,304 @@
+/*
+ * Copyright (c) 2015 Google, Inc
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ *
+ * EFI information obtained here:
+ * http://wiki.phoenix.com/wiki/index.php/EFI_BOOT_SERVICES
+ *
+ * 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>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+#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"
+#endif
+
+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')
+		putc('\r');
+}
+
+void puts(const char *str)
+{
+	while (*str)
+		putc(*str++);
+}
+
+static void _debug_uart_putc(int ch)
+{
+	putc(ch);
+}
+
+DEBUG_UART_FUNCS
+
+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)
+{
+#ifdef CONFIG_EFI_STUB_32BIT
+	/*
+	 * 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)
+		__attribute__((regparm(3)));
+
+	((func_t)addr)(0, 0, info);
+#else
+	/* TODO: Implement this */
+#endif
+}
+
+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) {
+		printhex2(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)
+		return EFI_UNSUPPORTED;
+
+	/* 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) {
+		printhex2(BITS_PER_LONG);
+		printhex2(ret);
+		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) {
+		printhex2(ret);
+		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) {
+		printhex2(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.
+		 */
+		printhex2(ret);
+		puts(" Can't exit boot services\n");
+		size = sizeof(desc);
+		ret = boot->get_memory_map(&size, desc, &key, &desc_size,
+					   &version);
+		if (ret) {
+			printhex2(ret);
+			puts(" Can't get memory map\n");
+			return ret;
+		}
+		ret = boot->exit_boot_services(image, key);
+		if (ret) {
+			printhex2(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 -
+	       (ulong)_binary_u_boot_dtb_bin_start);
+
+#ifdef DEBUG
+	puts("EFI table at ");
+	printhex8((ulong)priv->info);
+	puts(" size ");
+	printhex8(priv->info->total_size);
+#endif
+	putc('\n');
+	jump_to_uboot(cs32, CONFIG_SYS_TEXT_BASE, (ulong)priv->info);
+
+	return EFI_LOAD_ERROR;
+}