Re: [MULTIBOOT2 SPEC PATCH V2] multiboot2: Add module load and preference tag

[Daniel Kiper]

On Thu, May 07, 2020 at 03:09:23PM -0700, Zide Chen wrote:
> In the cases of users have preferences over Multiboot2 module load
> addresses, currently GRUB has no way to achieve it.
>
> Similar to the relocatable header tag, this new tag allows users to
> specify the minimum and maximum load addresses, and other load
> preferences on Multiboot2 modules.
>
> Signed-off-by: Zide Chen <address@hidden>
> ---
>  doc/multiboot.texi | 41 +++++++++++++++++++++++++++++++++++++++++
>  doc/multiboot2.h   | 11 +++++++++++
>  2 files changed, 52 insertions(+)
>
> diff --git a/doc/multiboot.texi b/doc/multiboot.texi
> index df8a0d056e76..758ef7fd1e2d 100644
> --- a/doc/multiboot.texi
> +++ b/doc/multiboot.texi
> @@ -356,6 +356,7 @@ executable header.
>  * Module alignment tag::
>  * EFI boot services tag::
>  * Relocatable header tag::
> +* Module load preferences tag::

Please bump spec version to 2.1.

>  @end menu
>
> @@ -730,6 +731,46 @@ Boot loader should follow it. @samp{0} means none, 
> @samp{1} means
>  load image at lowest possible address but not lower than min_addr
>  and @samp{2} means load image at highest possible address but not
>  higher than max_addr.
> +
> +@node Module load preferences tag
> +@subsection Module load preferences tag
> +
> +@example
> +@group
> +        +-------------------+
> +u16     | type = 11         |
> +u16     | flags             |
> +u32     | size = 20         |
> +u32     | min_addr          |
> +u32     | max_addr          |

I have an itching to add "align" member here like in the relocatable
header tag. I can imagine that some kernels may want aligned modules. If
you do that then we have to resolve conflict with the module alignment
tag. I think if both tags are in the image header then the bootloader
should use max(align, PAGE_SIZE). This behavior should be described in
one way or another next to both tags.

> +u32     | preference        |
> +        +-------------------+
> +@end group
> +@end example
> +

Please describe shortly what this tag does. You can find good example in
relocatable header tag.

> +This tag is independent to the relocatable header tag. All of the

This sentence should go to the end of the tag description.

> +address fields in this tag are physical addresses.
> +
> +The meaning of each field is as follows:
> +
> +@table @code
> +@item min_addr
> +Lowest possible physical address at which any modules should be
> +loaded. The bootloader cannot load any part of any modules below
> +this address.
> +
> +@item max_addr
> +Highest possible physical address at which any loaded modules should
> +end. The bootloader cannot load any part of any modules above this
> +address.
> +
> +@item preference
> +It contains load address placement suggestion for boot loader.
> +Boot loader should follow it. @samp{0} means load modules not lower
> +than min_addr and not higher than max_addr, but no preference on either
> +lower or higher address. @samp{1} means load modules at lowest possible
> +address but not lower than min_addr. @samp{2} means load modules at
> +highest possible address but not higher than max_addr.

Please copy preference description from relocatable header tag and
replace "image" with "module".

Daniel