Re: [Xen-devel] [MULTIBOOT2 DOC PATCH v2 05/11] multiboot2: Add description of support for EFI boot services

[Andrei Borzenkov <arvidjaar@xxxxxxxxx>]

24.11.2016 23:40, Daniel Kiper пишет:
> Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
> ---
> v2 - suggestions/fixes:
>    - clarify physical address meaning for EFI amd64
>      mode with boot services enabled
>      (suggested by Andrew Cooper).
> ---
>  doc/multiboot.texi |  115 
> +++++++++++++++++++++++++++++++++++++++++++++++++++-
>  doc/multiboot2.h   |    2 +
>  2 files changed, 115 insertions(+), 2 deletions(-)
> 
> diff --git a/doc/multiboot.texi b/doc/multiboot.texi
> index f0f167e..cc1edab 100644
> --- a/doc/multiboot.texi
> +++ b/doc/multiboot.texi
> @@ -534,6 +534,66 @@ The physical address to which the boot loader should 
> jump in order to
>  start running the operating system.
>  @end table
>  
> +@subsection EFI i386 entry address tag of Multiboot2 header
> +
> +@example
> +@group
> +        +-------------------+
> +u16     | type = 8          |
> +u16     | flags             |
> +u32     | size              |
> +u_virt  | entry_addr        |
> +        +-------------------+
> +@end group
> +@end example
> +
> +All of the address fields in this tag are physical addresses.

Should not entry_addr be u_phys then? Otherwise what is exact difference
between u_phys and u_virt? Also for type == 3?

> +The meaning of each is as follows:
> +
> +@table @code
> +
> +@item entry_addr
> +The physical address to which the boot loader should jump in order to
> +start running EFI i386 compatible operating system code.
> +@end table
> +
> +This tag is taken into account only on EFI i386 platforms
> +when Multiboot2 image header contains EFI boot services tag.
> +Then entry point specified in ELF header and the entry address
> +tag of Multiboot2 header are ignored.
> +
> +@subsection EFI amd64 entry address tag of Multiboot2 header
> +
> +@example
> +@group
> +        +-------------------+
> +u16     | type = 9          |
> +u16     | flags             |
> +u32     | size              |
> +u_virt  | entry_addr        |
> +        +-------------------+
> +@end group
> +@end example
> +
> +All of the address fields in this tag are physical addresses (paging
> +mode is enabled and any memory space defined by the UEFI memory map
> +is identity mapped, hence, virtual address equals physical address;

Same here; it is confusing marking field as u_virt and describing it
immediately as "physical address".

> +Unified Extensible Firmware Interface Specification, Version 2.6,
> +section 2.3.4, x64 Platforms, boot services). The meaning of each
> +is as follows:
> +
> +@table @code
> +
> +@item entry_addr
> +The physical address to which the boot loader should jump in order to
> +start running EFI amd64 compatible operating system code.
> +@end table
> +
> +This tag is taken into account only on EFI amd64 platforms
> +when Multiboot2 image header contains EFI boot services tag.
> +Then entry point specified in ELF header and the entry address
> +tag of Multiboot2 header are ignored.
> +

Why do we have two different tags for what is effectively the same
purpose? Is it possible for the same image to have both of them? Just
for my understanding.


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