[U-Boot] [PATCH 6/9] efi_loader: Add runtime services

[Leif Lindholm]

On Tue, Dec 22, 2015 at 02:57:53PM +0100, Alexander Graf wrote:
> After booting has finished, EFI allows firmware to still interact with the OS
> using the "runtime services". These callbacks live in a separate address space,
> since they are available long after U-Boot has been overwritten by the OS.
> 
> However, since U-Boot has no notion of RTS, we just create an extremely minimal
> RTS stub that just declares all functions as unsupported. We could in the future
> map U-boot environment variables to EFI variables here.
> 
> Signed-off-by: Alexander Graf <agraf at suse.de>
> ---
>  arch/arm/cpu/armv8/u-boot.lds |  8 ++++++
>  arch/arm/cpu/u-boot.lds       | 13 ++++++++++
>  arch/arm/lib/sections.c       |  2 ++
>  include/efi_loader.h          |  3 +++
>  lib/efi_loader/efi_runtime.c  | 59 +++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 85 insertions(+)
>  create mode 100644 lib/efi_loader/efi_runtime.c
> 
> diff --git a/arch/arm/cpu/armv8/u-boot.lds b/arch/arm/cpu/armv8/u-boot.lds
> index 4c12222..7c5b032 100644
> --- a/arch/arm/cpu/armv8/u-boot.lds
> +++ b/arch/arm/cpu/armv8/u-boot.lds
> @@ -42,6 +42,14 @@ SECTIONS
>  
>  	. = ALIGN(8);
>  
> +	.efi_runtime : {
> +                __efi_runtime_start = .;
> +		*(efi_runtime)
> +                __efi_runtime_stop = .;
> +	}
> +
> +	. = ALIGN(8);
> +
>  	.image_copy_end :
>  	{
>  		*(.__image_copy_end)
> diff --git a/arch/arm/cpu/u-boot.lds b/arch/arm/cpu/u-boot.lds
> index d48a905..b5198d0 100644
> --- a/arch/arm/cpu/u-boot.lds
> +++ b/arch/arm/cpu/u-boot.lds
> @@ -89,6 +89,19 @@ SECTIONS
>  
>  	. = ALIGN(4);
>  
> +	.__efi_runtime_start : {
> +		*(.__efi_runtime_start)
> +	}
> +
> +	.efi_runtime : {
> +		*(efi_runtime)
> +	}
> +
> +	.__efi_runtime_stop : {
> +		*(.__efi_runtime_stop)
> +	}
> +	. = ALIGN(4);
> +
>  	.image_copy_end :
>  	{
>  		*(.__image_copy_end)
> diff --git a/arch/arm/lib/sections.c b/arch/arm/lib/sections.c
> index a1205c3..21b3066 100644
> --- a/arch/arm/lib/sections.c
> +++ b/arch/arm/lib/sections.c
> @@ -27,4 +27,6 @@ char __rel_dyn_start[0] __attribute__((section(".__rel_dyn_start")));
>  char __rel_dyn_end[0] __attribute__((section(".__rel_dyn_end")));
>  char __secure_start[0] __attribute__((section(".__secure_start")));
>  char __secure_end[0] __attribute__((section(".__secure_end")));
> +char __efi_runtime_start[0] __attribute__((section(".__efi_runtime_start")));
> +char __efi_runtime_stop[0] __attribute__((section(".__efi_runtime_stop")));
>  char _end[0] __attribute__((section(".__end")));
> diff --git a/include/efi_loader.h b/include/efi_loader.h
> index 7fb2106..af1c88f 100644
> --- a/include/efi_loader.h
> +++ b/include/efi_loader.h
> @@ -39,6 +39,7 @@
>  
>  #define EFI_EXIT(ret) efi_exit_func(ret);
>  
> +extern const struct efi_runtime_services efi_runtime_services;
>  extern struct efi_system_table systab;
>  
>  extern const struct efi_simple_text_output_protocol efi_con_out;
> @@ -49,6 +50,8 @@ extern const efi_guid_t efi_guid_console_control;
>  extern const efi_guid_t efi_guid_device_path;
>  extern const efi_guid_t efi_guid_loaded_image;
>  
> +extern unsigned int __efi_runtime_start, __efi_runtime_stop;
> +
>  struct efi_class_map {
>  	const efi_guid_t *guid;
>  	const void *interface;
> diff --git a/lib/efi_loader/efi_runtime.c b/lib/efi_loader/efi_runtime.c
> new file mode 100644
> index 0000000..214e1f5
> --- /dev/null
> +++ b/lib/efi_loader/efi_runtime.c
> @@ -0,0 +1,59 @@
> +/*
> + *  EFI application runtime services
> + *
> + *  Copyright (c) 2015 Alexander Graf
> + *
> + *  This library is free software; you can redistribute it and/or
> + *  modify it under the terms of the GNU Lesser General Public
> + *  License as published by the Free Software Foundation; either
> + *  version 2.1 of the License, or (at your option) any later version.
> + *
> + *  This library is distributed in the hope that it will be useful,
> + *  but WITHOUT ANY WARRANTY; without even the implied warranty of
> + *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + *  Lesser General Public License for more details.
> + *
> + *  You should have received a copy of the GNU Lesser General Public
> + *  License along with this library; if not, write to the Free Software
> + *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
> + *
> + *  SPDX-License-Identifier:     LGPL-2.1+
> + */
> +
> +#include <common.h>
> +#include <efi_loader.h>
> +
> +/*
> + * EFI Runtime code is still alive when U-Boot is long overwritten. To isolate
> + * this code from the rest, we put it into a special section.
> + *
> + *        !!WARNING!!
> + *
> + * This means that we can not rely on any code outside of this file at runtime.
> + * Please keep it fully self-contained.
> + */
> +asm(".section efi_runtime,\"a\"");
> +
> +static efi_status_t efi_unimplemented(void)
> +{
> +	return EFI_UNSUPPORTED;

Again, EFI_UNSUPPORTED is not necessarily a valid return value for all
runtime services.

> +}
> +
> +const struct efi_runtime_services efi_runtime_services = {
> +	.hdr = {
> +		.signature = EFI_RUNTIME_SERVICES_SIGNATURE,
> +		.revision = EFI_RUNTIME_SERVICES_REVISION,
> +		.headersize = sizeof(struct efi_table_hdr),
> +	},
> +	.get_time = (void *)&efi_unimplemented,

EFI_DEVICE_ERROR

> +	.set_time = (void *)&efi_unimplemented,

EFI_DEVICE_ERROR

> +	.get_wakeup_time = (void *)&efi_unimplemented,
> +	.set_wakeup_time = (void *)&efi_unimplemented,

Both of these are fine, and correct, to return EFI_UNSUPPORTED.

> +	.set_virtual_address_map = (void *)&efi_unimplemented,
> +	.convert_pointer = (void *)&efi_unimplemented,

There really isn't a way to gracefully decline these two functions.
All valid error codes refer to invalid inputs.

> +	.get_variable = (void *)&efi_unimplemented,

EFI_DEVICE_ERROR would probably be the closest thing to a correct
return code in this instance.

> +	.get_next_variable = (void *)&efi_unimplemented,

(get_next_variable_name?)
Again, EFI_DEVICE_ERROR, is probably the least wrong return value.

> +	.set_variable = (void *)&efi_unimplemented,

EFI_DEVICE_ERROR

> +	.get_next_high_mono_count = (void *)&efi_unimplemented,

EFI_DEVICE_ERROR

> +	.reset_system = (void *)&efi_unimplemented,

"The ResetSystem() function does not return."

> +};
> -- 
> 2.1.4