Re: [RFC PATCH 0/9] arm64: Allocate .text and .init.text together

[Petr Pavlu]

On 8/22/26 3:53 PM, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@xxxxxxxxxx>
> 
> The arm64 module loader has to deal with a couple of corner cases that
> may occur when .init.text is placed out of direct branch range of .text:
> 
> - ordinary direct branches from .init.text into .text may require the
>   use of a PLT entry (i.e., a trampoline aka veneer), which means not
>   only that additional PLT entries need to be allocated for
>   cross-section calls, but also that .init.text needs its own PLT
>   reservation, as the one in .text will be out of range as well;
> 
> - dynamic patching of the ftrace handler into .init.text code needs its
>   own dedicated trampoline as the one in .text may be too far away.
> 
> - recent compilers may omit BTI veneers for static functions that never
>   have their address taken, and so additional veneers will need to be
>   added to .text in case cross-section direct branches from .init.text 
>   require a PLT entry (and therefore a landing pad at the target end).
> 
> This is unfortunate, because it is actually somewhat unusual for .text
> and .init.text to be so far away from each other: only when allocating
> either of them (but not both) exhausts the 'near' (PLT-less) module
> region, the other will be allocated from the spillover region, which is
> not in direct branching range, and therefore requires PLT entries for
> cross-section calls.
> 
> This series addresses this wart by allocating both of them as a single
> chunk, and freeing the .init.text part along with the other init
> sections at the appropriate time. This ensures that the two regions will
> never require veneers for cross-section calls, allowing the arm64 module
> loader to be simplified.

It looks like this should also be useful for ppc64, which currently
merges .init.text and .text because keeping them separate would require
stubs between the two, and consequently .init.text is never released in
modules on this architecture.

-- 
Thanks,
Petr