Re: [PATCH v7 1/5] x86/boot: Rework how 32bit C is linked/included for early boot

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 29/10/2024 10:29 am, Frediano Ziglio wrote:
> Right now, the two functions which were really too complicated to write
> in asm are compiled as 32bit PIC, linked to a blob and included
> directly, using global asm() to arrange for them to have function semantics.
>
> This is limiting and fragile; the use of data relocations will compile
> fine but malfunction when used, creating hard-to-debug bugs.
>
> Furthermore, we would like to increase the amount of C, to
> deduplicate/unify Xen's boot logic, as well as making it easier to
> follow.  Therefore, rework how the 32bit objects are included.
>
> Link all 32bit objects together first.  This allows for sharing of logic
> between translation units.  Use differential linking and explicit
> imports/exports to confirm that we only have the expected relocations,
> and write the object back out as an assembly file so it can be linked
> again as if it were 64bit, to integrate with the rest of Xen.
>
> This allows for the use of external references (e.g. access to global
> variables) with reasonable assurance of doing so safely.
>
> No functional change.
>
> Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com>
> Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>