Re: [PATCH 15/16] Add EFI stub for ARM

Dave Martin
2013-08-13T14:19:48Z

On Fri, Aug 09, 2013 at 04:26:16PM -0700, Roy Franz wrote:
> This patch adds EFI stub support for the ARM Linux kernel. The EFI stub
> operations similarly to the x86 stub: it is a shim between the EFI firmware
> and the normal zImage entry point, and sets up the environment that the
> zImage is expecting. This includes loading the initrd (optionaly) and
> device tree from the system partition based on the kernel command line.
> The stub updates the device tree as necessary, including adding reserved
> memory regions and adding entries for EFI runtime services. The PE/COFF
> "MZ" header at offset 0 results in the first instruction being an add
> that corrupts r5, which is not used by the zImage interface.

Thanks for the update -- a few more comments, nothing major.

> Signed-off-by: Roy Franz <roy.franz-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> ---
> arch/arm/boot/compressed/Makefile | 15 +-
> arch/arm/boot/compressed/efi-header.S | 111 ++++++++
> arch/arm/boot/compressed/efi-stub.c | 448 +++++++++++++++++++++++++++++++++
> arch/arm/boot/compressed/efi-stub.h | 5 +
> arch/arm/boot/compressed/head.S | 90 ++++++-
> 5 files changed, 661 insertions(+), 8 deletions(-)
> create mode 100644 arch/arm/boot/compressed/efi-header.S
> create mode 100644 arch/arm/boot/compressed/efi-stub.c
> create mode 100644 arch/arm/boot/compressed/efi-stub.h
>
> diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> index 7ac1610..5fad8bd 100644
> --- a/arch/arm/boot/compressed/Makefile
> +++ b/arch/arm/boot/compressed/Makefile
> @@ -103,11 +103,22 @@ libfdt_objs := $(addsuffix .o, $(basename $(libfdt)))
> $(addprefix $(obj)/,$(libfdt) $(libfdt_hdrs)): $(obj)/%: $(srctree)/scripts/dtc/libfdt/%
> $(call cmd,shipped)
>
> -$(addprefix $(obj)/,$(libfdt_objs) atags_to_fdt.o): \
> +$(addprefix $(obj)/,$(libfdt_objs) atags_to_fdt.o efi-stub.o): \
> $(addprefix $(obj)/,$(libfdt_hdrs))
>
> ifeq ($(CONFIG_ARM_ATAG_DTB_COMPAT),y)
> -OBJS += $(libfdt_objs) atags_to_fdt.o
> +OBJS += atags_to_fdt.o
> +USE_LIBFDT = y
> +endif
> +
> +ifeq ($(CONFIG_EFI_STUB),y)
> +CFLAGS_efi-stub.o += -DTEXT_OFFSET=$(TEXT_OFFSET)
> +OBJS += efi-stub.o
> +USE_LIBFDT = y
> +endif
> +
> +ifeq ($(USE_LIBFDT),y)
> +OBJS += $(libfdt_objs)
> endif
>
> targets := vmlinux vmlinux.lds \
> diff --git a/arch/arm/boot/compressed/efi-header.S b/arch/arm/boot/compressed/efi-header.S
> new file mode 100644
> index 0000000..6965e0f
> --- /dev/null
> +++ b/arch/arm/boot/compressed/efi-header.S
> @@ -0,0 +1,111 @@
> +@ Copyright (C) 2013 Linaro Ltd; <roy.franz-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> +@
> +@ This file contains the PE/COFF header that is part of the
> +@ EFI stub.
> +@
> +
> + .org 0x3c
> + @
> + @ The PE header can be anywhere in the file, but for
> + @ simplicity we keep it together with the MSDOS header
> + @ The offset to the PE/COFF header needs to be at offset
> + @ 0x3C in the MSDOS header.
> + @ The only 2 fields of the MSDOS header that are used are this
> + @ PE/COFF offset, and the "MZ" bytes at offset 0x0.
> + @
> + .long pe_header @ Offset to the PE header.
> +
> + .align 3
> +pe_header:
> + .ascii "PE"
> + .short 0
> +
> +coff_header:
> + .short 0x01c2 @ ARM or Thumb
> + .short 2 @ nr_sections
> + .long 0 @ TimeDateStamp
> + .long 0 @ PointerToSymbolTable
> + .long 1 @ NumberOfSymbols
> + .short section_table - optional_header @ SizeOfOptionalHeader
> + .short 0x306 @ Characteristics.
> + @ IMAGE_FILE_32BIT_MACHINE |
> + @ IMAGE_FILE_DEBUG_STRIPPED |
> + @ IMAGE_FILE_EXECUTABLE_IMAGE |
> + @ IMAGE_FILE_LINE_NUMS_STRIPPED
> +
> +optional_header:
> + .short 0x10b @ PE32 format
> + .byte 0x02 @ MajorLinkerVersion
> + .byte 0x14 @ MinorLinkerVersion
> +
> + .long _edata - efi_stub_entry @ SizeOfCode
> +
> + .long 0 @ SizeOfInitializedData
> + .long 0 @ SizeOfUninitializedData
> +
> + .long efi_stub_entry @ AddressOfEntryPoint
> + .long efi_stub_entry @ BaseOfCode
> + .long 0 @ data
> +
> +extra_header_fields:
> + .long 0 @ ImageBase
> + .long 0x20 @ SectionAlignment
> + .long 0x20 @ FileAlignment
> + .short 0 @ MajorOperatingSystemVersion
> + .short 0 @ MinorOperatingSystemVersion
> + .short 0 @ MajorImageVersion
> + .short 0 @ MinorImageVersion
> + .short 0 @ MajorSubsystemVersion
> + .short 0 @ MinorSubsystemVersion
> + .long 0 @ Win32VersionValue
> +
> + .long _edata @ SizeOfImage
> +
> + @ Everything before the entry point is considered part of the header
> + .long efi_stub_entry @ SizeOfHeaders
> + .long 0 @ CheckSum
> + .short 0xa @ Subsystem (EFI application)
> + .short 0 @ DllCharacteristics
> + .long 0 @ SizeOfStackReserve
> + .long 0 @ SizeOfStackCommit
> + .long 0 @ SizeOfHeapReserve
> + .long 0 @ SizeOfHeapCommit
> + .long 0 @ LoaderFlags
> + .long 0x0 @ NumberOfRvaAndSizes
> +
> + # Section table
> +section_table:
> +
> + #
> + # The EFI application loader requires a relocation section
> + # because EFI applications must be relocatable. This is a
> + # dummy section as far as we are concerned.
> + #
> + .ascii ".reloc"
> + .byte 0
> + .byte 0 @ end of 0 padding of section name
> + .long 0
> + .long 0
> + .long 0 @ SizeOfRawData
> + .long 0 @ PointerToRawData
> + .long 0 @ PointerToRelocations
> + .long 0 @ PointerToLineNumbers
> + .short 0 @ NumberOfRelocations
> + .short 0 @ NumberOfLineNumbers
> + .long 0x42100040 @ Characteristics (section flags)
> +
> +
> + .ascii ".text"
> + .byte 0
> + .byte 0
> + .byte 0 @ end of 0 padding of section name
> + .long _edata - efi_stub_entry @ VirtualSize
> + .long efi_stub_entry @ VirtualAddress
> + .long _edata - efi_stub_entry @ SizeOfRawData
> + .long efi_stub_entry @ PointerToRawData
> +
> + .long 0 @ PointerToRelocations (0 for executables)
> + .long 0 @ PointerToLineNumbers (0 for executables)
> + .short 0 @ NumberOfRelocations (0 for executables)
> + .short 0 @ NumberOfLineNumbers (0 for executables)
> + .long 0xe0500020 @ Characteristics (section flags)
> diff --git a/arch/arm/boot/compressed/efi-stub.c b/arch/arm/boot/compressed/efi-stub.c
> new file mode 100644
> index 0000000..4fce68b
> --- /dev/null
> +++ b/arch/arm/boot/compressed/efi-stub.c
> @@ -0,0 +1,448 @@
> +/*
> + * linux/arch/arm/boot/compressed/efi-stub.c
> + *
> + * Copyright (C) 2013 Linaro Ltd; <roy.franz-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> + *
> + * This file implements the EFI boot stub for the ARM kernel
> + *
> + * 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.
> + *
> + */
> +#include <linux/efi.h>
> +#include <libfdt.h>
> +#include "efi-stub.h"
> +
> +/* EFI function call wrappers. These are not required for
> + * ARM, but wrappers are required for X86 to convert between
> + * ABIs. These wrappers are provided to allow code sharing
> + * between X86 and ARM. Since these wrappers directly invoke the
> + * EFI function pointer, the function pointer type must be properly
> + * defined, which is not the case for X86 One advantage of this is
> + * it allows for type checking of arguments, which is not
> + * possible with the X86 wrappers.
> + */
> +#define efi_call_phys0(f) f()
> +#define efi_call_phys1(f, a1) f(a1)
> +#define efi_call_phys2(f, a1, a2) f(a1, a2)
> +#define efi_call_phys3(f, a1, a2, a3) f(a1, a2, a3)
> +#define efi_call_phys4(f, a1, a2, a3, a4) f(a1, a2, a3, a4)
> +#define efi_call_phys5(f, a1, a2, a3, a4, a5) f(a1, a2, a3, a4, a5)
> +
> +/* The maximum uncompressed kernel size is 32 MBytes, so we will reserve
> + * that for the decompressed kernel. We have no easy way to tell what
> + * the actuall size of code + data the uncompressed kernel will use.
> + */
> +#define MAX_UNCOMP_KERNEL_SIZE 0x02000000
> +
> +/* The kernel zImage should be located between 32 Mbytes
> + * and 128 MBytes from the base of DRAM. The min
> + * address leaves space for a maximal size uncompressed image,
> + * and the max address is due to how the zImage decompressor
> + * picks a destination address.
> + */
> +#define ZIMAGE_OFFSET_LIMIT 0x08000000
> +#define MIN_ZIMAGE_OFFSET MAX_UNCOMP_KERNEL_SIZE
> +
> +#define PRINTK_PREFIX "EFIstub: "
> +
> +struct fdt_region {
> + u64 base;
> + u64 size;
> +};
> +
> +
> +/* Include shared EFI stub code */
> +#include "../../../../drivers/firmware/efi/efi-stub-helper.c"
> +
> +static int relocate_kernel(efi_system_table_t *sys_table,
> + unsigned long *zimage_addr,
> + unsigned long zimage_size,
> + unsigned long min_addr, unsigned long max_addr)
> +{
> + /* Get current address of kernel. */
> + unsigned long cur_zimage_addr = *zimage_addr;
> + unsigned long new_addr = 0;
> +
> + efi_status_t status;
> +
> + if (!zimage_addr || !zimage_size)
> + return EFI_INVALID_PARAMETER;
> +
> + if (cur_zimage_addr > min_addr
> + && (cur_zimage_addr + zimage_size) < max_addr) {
> + /* We don't need to do anything, as kernel is at an
> + * acceptable address already.
> + */
> + return EFI_SUCCESS;
> + }
> + /*
> + * The EFI firmware loader could have placed the kernel image
> + * anywhere in memory, but the kernel has restrictions on the
> + * min and max physical address it can run at.
> + */
> + status = efi_low_alloc(sys_table, zimage_size, 0,
> + &new_addr, min_addr);
> + if (status != EFI_SUCCESS) {
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: Failed to allocate usable memory for kernel.\n");
> + return status;
> + }
> +
> + if (new_addr > (max_addr - zimage_size)) {
> + efi_free(sys_table, zimage_size, new_addr);
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: Failed to allocate usable memory for kernel.\n");
> + return EFI_INVALID_PARAMETER;
> + }
> +
> + /* We know source/dest won't overlap since both memory ranges
> + * have been allocated by UEFI, so we can safely use memcpy.
> + */
> + memcpy((void *)new_addr, (void *)(unsigned long)cur_zimage_addr,
> + zimage_size);
> +
> + /* Return the load address */
> + *zimage_addr = new_addr;
> +
> + return status;
> +}
> +
> +
> +/* Convert the unicode UEFI command line to ASCII to pass to kernel.
> + * Size of memory allocated return in *cmd_line_len.
> + * Returns NULL on error.
> + */
> +static char *convert_cmdline_to_ascii(efi_system_table_t *sys_table,
> + efi_loaded_image_t *image,
> + unsigned long *cmd_line_len,
> + u32 max_addr)
> +{
> + u16 *s2;
> + u8 *s1 = NULL;
> + unsigned long cmdline_addr = 0;
> + int load_options_size = image->load_options_size / 2; /* ASCII */
> + void *options = (u16 *)image->load_options;
> + int options_size = 0;
> + int status;
> + int i;
> + u16 zero = 0;
> +
> + if (options) {
> + s2 = options;
> + while (*s2 && *s2 != '\n' && options_size < load_options_size) {
> + s2++;
> + options_size++;
> + }
> + }
> +
> + if (options_size == 0) {
> + /* No command line options, so return empty string*/
> + options_size = 1;
> + options = &zero;
> + }
> +
> + options_size++; /* NUL termination */
> +
> + status = efi_high_alloc(sys_table, options_size, 0,
> + &cmdline_addr, max_addr);
> + if (status != EFI_SUCCESS)
> + return NULL;
> +
> + s1 = (u8 *)(unsigned long)cmdline_addr;
> + s2 = (u16 *)options;
> +
> + for (i = 0; i < options_size - 1; i++)
> + *s1++ = *s2++;
> +
> + *s1 = '\0';
> +
> + *cmd_line_len = options_size;
> + return (char *)(unsigned long)cmdline_addr;
> +}
> +
> +
> +static u32 update_fdt(efi_system_table_t *sys_table, void *orig_fdt, void *fdt,
> + int new_fdt_size, char *cmdline_ptr, u64 initrd_addr,
> + u64 initrd_size, efi_memory_desc_t *memory_map,
> + int map_size, int desc_size)
> +{
> + int node;
> + int status;
> + unsigned long fdt_val;
> +
> + status = fdt_open_into(orig_fdt, fdt, new_fdt_size);
> + if (status != 0)
> + goto fdt_set_fail;
> +
> + node = fdt_subnode_offset(fdt, 0, "chosen");
> + if (node < 0) {
> + node = fdt_add_subnode(fdt, 0, "chosen");
> + if (node < 0) {
> + status = node; /* node is error code when negative */
> + goto fdt_set_fail;
> + }
> + }
> +
> + if ((cmdline_ptr != NULL) && (strlen(cmdline_ptr) > 0)) {
> + status = fdt_setprop(fdt, node, "bootargs", cmdline_ptr,
> + strlen(cmdline_ptr) + 1);
> + if (status)
> + goto fdt_set_fail;
> + }
> +
> + /* Set intird address/end in device tree, if present */
> + if (initrd_size != 0) {
> + u64 initrd_image_end;
> + u64 initrd_image_start = cpu_to_fdt64(initrd_addr);
> + status = fdt_setprop(fdt, node, "linux,initrd-start",
> + &initrd_image_start, sizeof(u64));
> + if (status)
> + goto fdt_set_fail;
> + initrd_image_end = cpu_to_fdt64(initrd_addr + initrd_size);
> + status = fdt_setprop(fdt, node, "linux,initrd-end",
> + &initrd_image_end, sizeof(u64));
> + if (status)
> + goto fdt_set_fail;
> + }
> +
> + /* Add FDT entries for EFI runtime services in chosen node. */
> + node = fdt_subnode_offset(fdt, 0, "chosen");
> + fdt_val = cpu_to_fdt32((unsigned long)sys_table);
> + status = fdt_setprop(fdt, node, "efi-system-table",
> + &fdt_val, sizeof(fdt_val));
> + if (status)
> + goto fdt_set_fail;
> +
> + fdt_val = cpu_to_fdt32(desc_size);
> + status = fdt_setprop(fdt, node, "efi-mmap-desc-size",
> + &fdt_val, sizeof(fdt_val));
> + if (status)
> + goto fdt_set_fail;
> +
> + fdt_val = cpu_to_fdt32(map_size);
> + status = fdt_setprop(fdt, node, "efi-runtime-mmap-size",
> + &fdt_val, sizeof(fdt_val));
> + if (status)
> + goto fdt_set_fail;
> +
> + fdt_val = cpu_to_fdt32((unsigned long)memory_map);
> + status = fdt_setprop(fdt, node, "efi-runtime-mmap",
> + &fdt_val, sizeof(fdt_val));
> + if (status)
> + goto fdt_set_fail;
> +
> + return EFI_SUCCESS;

This looks better.

> +
> +fdt_set_fail:
> + if (status == -FDT_ERR_NOSPACE)
> + return EFI_BUFFER_TOO_SMALL;
> +
> + return EFI_LOAD_ERROR;
> +}
> +
> +
> +

Maybe add a comment to indicate that this returns the address of the
relocated fdt, or EFI_LOAD_ERROR.

By default "int" feels more likely to return a status code.

It is not common to return pointers using the "int" type: it may be
preferable to use unsigned long of void * instead. This won't
change the functionality.

Casts to (int) which could overflow the signed range can cause GCC
to generate bizarre code in some situations, because C doesn't
have to guarantee wrapping when casting to signed types. Since we
just pass that value through without doing any arithmetic I think we're
unlikely to hit that here, but it's best avoided anyhow.

> +int efi_entry(void *handle, efi_system_table_t *sys_table,
> + unsigned long *zimage_addr)
> +{
> + efi_loaded_image_t *image;
> + int status;
> + unsigned long nr_pages;
> + const struct fdt_region *region;
> +
> + void *fdt;
> + int err;
> + int node;
> + unsigned long zimage_size = 0;
> + unsigned long dram_base;
> + /* addr/point and size pairs for memory management*/
> + u64 initrd_addr;
> + u64 initrd_size = 0;
> + u64 fdt_addr;
> + u64 fdt_size = 0;
> + u64 kernel_reserve_addr;
> + u64 kernel_reserve_size = 0;
> + char *cmdline_ptr;
> + unsigned long cmdline_size = 0;
> +
> + unsigned long map_size, desc_size;
> + unsigned long mmap_key;
> + efi_memory_desc_t *memory_map;
> +
> + unsigned long new_fdt_size;
> + unsigned long new_fdt_addr;
> +
> + efi_guid_t proto = LOADED_IMAGE_PROTOCOL_GUID;
> +
> + /* Check if we were booted by the EFI firmware */
> + if (sys_table->hdr.signature != EFI_SYSTEM_TABLE_SIGNATURE)
> + goto fail;
> +
> + efi_printk(sys_table, PRINTK_PREFIX"Booting Linux using EFI stub.\n");
> +
> +
> + /* get the command line from EFI, using the LOADED_IMAGE protocol */
> + status = efi_call_phys3(sys_table->boottime->handle_protocol,
> + handle, &proto, (void *)&image);
> + if (status != EFI_SUCCESS) {
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: Failed to get handle for LOADED_IMAGE_PROTOCOL\n");
> + goto fail;
> + }
> +
> + /* We are going to copy this into device tree, so we don't care where in
> + * memory it is.
> + */
> + cmdline_ptr = convert_cmdline_to_ascii(sys_table, image,
> + &cmdline_size, 0xFFFFFFFF);
> + if (!cmdline_ptr) {
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: converting command line to ascii failed.\n");

The real reason for this failure is failure to allocate memory: there's
no other way it can fail.

So, the error message could be "Unable to allocate memory for command
line"

> + goto fail;
> + }
> +
> + /* We first load the device tree, as we need to get the base address of
> + * DRAM from the device tree. The zImage, device tree, and initrd
> + * have address restrictions that are relative to the base of DRAM.
> + */
> + status = handle_cmdline_files(sys_table, image, cmdline_ptr, "dtb=",
> + 0xffffffff, &fdt_addr, &fdt_size);
> + if (status != EFI_SUCCESS) {
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: Unable to load device tree blob.\n");
> + goto fail_free_cmdline;
> + }
> +
> + err = fdt_check_header((void *)(unsigned long)fdt_addr);
> + if (err != 0) {
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: device tree header not valid\n");
> + goto fail_free_fdt;
> + }
> + if (fdt_totalsize((void *)(unsigned long)fdt_addr) > fdt_size) {
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: Incomplete device tree.\n");
> + goto fail_free_fdt;
> +
> + }
> +
> +
> + /* Look up the base of DRAM from the device tree.*/
> + fdt = (void *)(u32)fdt_addr;
> + node = fdt_subnode_offset(fdt, 0, "memory");
> + region = fdt_getprop(fdt, node, "reg", NULL);
> + if (region) {
> + dram_base = fdt64_to_cpu(region->base);
> + } else {
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: no 'memory' node in device tree.\n");
> + goto fail_free_fdt;
> + }
> +
> + /* Reserve memory for the uncompressed kernel image. */
> + kernel_reserve_addr = dram_base;
> + kernel_reserve_size = MAX_UNCOMP_KERNEL_SIZE;
> + nr_pages = round_up(kernel_reserve_size, EFI_PAGE_SIZE) / EFI_PAGE_SIZE;
> + status = efi_call_phys4(sys_table->boottime->allocate_pages,
> + EFI_ALLOCATE_ADDRESS, EFI_LOADER_DATA,
> + nr_pages, &kernel_reserve_addr);
> + if (status != EFI_SUCCESS) {
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: unable to allocate memory for uncompressed kernel.\n");
> + goto fail_free_fdt;
> + }
> +
> + /* Relocate the zImage, if required. */
> + zimage_size = image->image_size;
> + status = relocate_kernel(sys_table, zimage_addr, zimage_size,
> + dram_base + MIN_ZIMAGE_OFFSET,
> + dram_base + ZIMAGE_OFFSET_LIMIT);
> + if (status != EFI_SUCCESS) {
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: Failed to relocate kernel\n");
> + goto fail_free_kernel_reserve;
> + }
> +
> + status = handle_cmdline_files(sys_table, image, cmdline_ptr, "initrd=",
> + dram_base + ZIMAGE_OFFSET_LIMIT,
> + &initrd_addr, &initrd_size);
> + if (status != EFI_SUCCESS) {
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: Unable to load initrd\n");
> + goto fail_free_zimage;
> + }
> +
> + /* Estimate size of new FDT, and allocate memory for it. We
> + * will allocate a bigger buffer if this ends up being too
> + * small, so a rough guess is OK here.*/
> + new_fdt_size = fdt_size + cmdline_size + 0x200;
> +
> +fdt_alloc_retry:

Minor stylistic thing, but looping using goto is not too readable.

The following while loop might be a bit clearer, but I leave it
up to you.

while (1) {

> + status = efi_high_alloc(sys_table, new_fdt_size, 0, &new_fdt_addr,
> + dram_base + ZIMAGE_OFFSET_LIMIT);
> + if (status != EFI_SUCCESS) {
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: Unable to allocate memory for new device tree.\n");
> + goto fail_free_initrd;
> + }
> +
> + /* Now that we have done our final memory allocation (and free)
> + * we can get the memory map key needed
> + * forexit_boot_services.*/
> + status = efi_get_memory_map(sys_table, &memory_map, &map_size,
> + &desc_size, &mmap_key);
> + if (status != EFI_SUCCESS)
> + goto fail_free_new_fdt;
> +
> + status = update_fdt(sys_table,
> + fdt, (void *)new_fdt_addr, new_fdt_size,
> + cmdline_ptr,
> + initrd_addr, initrd_size,
> + memory_map, map_size, desc_size);

if (status == EFI_SUCCESS)
break;

instead of

> +
> + if (status != EFI_SUCCESS) {

then

if (status != EFI_BUFFER_TOO_SMALL)
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: Unable to constuct new device tree.\n");
> + goto fail_free_initrd;

instead of

> + if (status == EFI_BUFFER_TOO_SMALL) {

then

> + /* We need to allocate more space for the new
> + * device tree, so free existing buffer that is
> + * too small. Also free memory map, as we will need
> + * to get new one that reflects the free/alloc we do
> + * on the device tree buffer. */
> + efi_free(sys_table, new_fdt_size, new_fdt_addr);
> + efi_call_phys1(sys_table->boottime->free_pool,
> + memory_map);
> + new_fdt_size += new_fdt_size/4;

And then just loop
}

instead of the rest:

> + goto fdt_alloc_retry;
> + }
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: Unable to constuct new device tree.\n");
> + goto fail_free_initrd;
> + }
> +
> + /* Now we are ready to exit_boot_services.*/
> + status = efi_call_phys2(sys_table->boottime->exit_boot_services,
> + handle, mmap_key);
> +
> + if (status != EFI_SUCCESS) {
> + efi_printk(sys_table, PRINTK_PREFIX"ERROR: exit boot services failed.\n");
> + goto fail_free_mmap;
> + }
> +
> +
> + /* Now we need to return the FDT address to the calling
> + * assembly to this can be used as part of normal boot.
> + */
> + return new_fdt_addr;
> +
> +fail_free_mmap:
> + efi_call_phys1(sys_table->boottime->free_pool, memory_map);
> +
> +fail_free_new_fdt:
> + efi_free(sys_table, new_fdt_size, new_fdt_addr);
> +
> +fail_free_initrd:
> + efi_free(sys_table, initrd_size, initrd_addr);
> +
> +fail_free_zimage:
> + efi_free(sys_table, zimage_size, *zimage_addr);
> +
> +fail_free_kernel_reserve:
> + efi_free(sys_table, kernel_reserve_addr, kernel_reserve_size);
> +
> +fail_free_fdt:
> + efi_free(sys_table, fdt_size, fdt_addr);
> +
> +fail_free_cmdline:
> + efi_free(sys_table, cmdline_size, (u32)cmdline_ptr);
> +
> +fail:
> + return EFI_STUB_ERROR;
> +}
> diff --git a/arch/arm/boot/compressed/efi-stub.h b/arch/arm/boot/compressed/efi-stub.h
> new file mode 100644
> index 0000000..0fe9376
> --- /dev/null
> +++ b/arch/arm/boot/compressed/efi-stub.h
> @@ -0,0 +1,5 @@
> +#ifndef _ARM_EFI_STUB_H
> +#define _ARM_EFI_STUB_H
> +/* Error code returned to ASM code instead of valid FDT address. */
> +#define EFI_STUB_ERROR (~0)
> +#endif
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index 75189f1..5401a3a 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -10,6 +10,7 @@
> */
> #include <linux/linkage.h>
> #include <asm/assembler.h>
> +#include "efi-stub.h"
>
> .arch armv7-a
> /*
> @@ -120,21 +121,99 @@
> */
> .align
> .arm @ Always enter in ARM state
> + .text
> start:
> .type start,#function
> - .rept 7
> +#ifdef CONFIG_EFI_STUB
> + @ Magic MSDOS signature for PE/COFF + ADD opcode
> + .word 0x62805a4d
> +#else
> + mov r0, r0
> +#endif
> + .rept 5
> mov r0, r0
> .endr
> - ARM( mov r0, r0 )
> - ARM( b 1f )
> - THUMB( adr r12, BSYM(1f) )
> - THUMB( bx r12 )
> +
> + adrl r12, BSYM(zimage_continue)
> + ARM( mov pc, r12 )
> + THUMB( bx r12 )
> + @ zimage_continue will be in ARM or thumb mode as configured
>
> .word 0x016f2818 @ Magic numbers to help the loader
> .word start @ absolute load/run zImage address
> .word _edata @ zImage end address
> +
> +#ifdef CONFIG_EFI_STUB
> + @ Portions of the MSDOS file header must be at offset
> + @ 0x3c from the start of the file. All PE/COFF headers
> + @ are kept contiguous for simplicity.
> +#include "efi-header.S"
> +
> +efi_stub_entry:
> + @ The EFI stub entry point is not at a fixed address, however
> + @ this address must be set in the PE/COFF header.
> + @ EFI entry point is in A32 mode, switch to T32 if configured.
> + THUMB( adr r12, BSYM(1f) )
> + THUMB( bx r12 )
> THUMB( .thumb )
> 1:
> + @ Save lr on stack for possible return to EFI firmware.
> + @ Don't care about fp, but need 64 bit alignment....
> + stmfd sp!, {fp, lr}
> +
> + @ allocate space on stack for return of new entry point of
> + @ zImage, as EFI stub may copy the kernel. Pass address
> + @ of space in r2 - EFI stub will fill in the pointer.
> +
> + sub sp, sp, #8 @ we only need 4 bytes,
> + @ but keep stack 8 byte aligned.
> + mov r2, sp

You can save an instruction here: skip these two instructions, and see
below just before the call to efi_entry [1]

> + @ Pass our actual runtime start address in pointer data
> + adr r11, LC0 @ address of LC0 at run time
> + ldr r12, [r11, #0] @ address of LC0 at link time

Can we just move this delta calculation after efi_entry?

You don't need to specifiy an explicit offset if it's zero, btw:

ldr r12, [r11]

works just as well. Same for the other instances.

> +
> + sub r3, r11, r12 @ calculate the delta offset
> + str r3, [r2, #0]

I think r2 is still equal to sp, so

str r3, [sp]

should be OK.

[1]Or, combine this with the modification of sp:

str r3, [sp, #-8]!
mov r2, sp

> + bl efi_entry
> +
> + @ get new zImage entry address from stack, put into r3
> + ldr r3, [sp, #0]
> + add sp, sp, #8 @ restore stack

ldr r3, [sp], #8

> +
> + @ Check for error return from EFI stub
> + mov r1, #EFI_STUB_ERROR
> + cmp r0, r1

cmp r0, #EFI_STUB_ERROR

probably works. The assembler will turn this into a cmn as necessary.

> + beq efi_load_fail
> +
> +
> + @ Save return values of efi_entry
> + stmfd sp!, {r0, r3}
> + bl cache_clean_flush
> + bl cache_off
> + ldmfd sp!, {r0, r3}
> +
> + @ Set parameters for booting zImage according to boot protocol
> + @ put FDT address in r2, it was returned by efi_entry()
> + @ r1 is FDT machine type, and r0 needs to be 0
> + mov r2, r0
> + mov r1, #0xFFFFFFFF
> + mov r0, #0
> +
> + @ Branch to (possibly) relocated zImage that is in r3
> + @ Make sure we are in A32 mode, as zImage requires
> + THUMB( bx r3 )
> + ARM( mov pc, r3 )
> +
> +efi_load_fail:
> + @ Return EFI_LOAD_ERROR to EFI firmware on error.
> + @ Switch back to ARM mode for EFI is done based on
> + @ return address on stack
> + ldr r0, =0x80000001
> + ldmfd sp!, {fp, pc}
> +#endif
> +
> + THUMB( .thumb )
> +zimage_continue:
> mrs r9, cpsr
> #ifdef CONFIG_ARM_VIRT_EXT
> bl __hyp_stub_install @ get into SVC mode, reversibly
> @@ -167,7 +246,6 @@ not_angel:
> * by the linker here, but it should preserve r7, r8, and r9.
> */
>
> - .text
>
> #ifdef CONFIG_AUTO_ZRELADDR
> @ determine final kernel image address
> --
> 1.7.10.4
>
>
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