Re: [PATCH v2 09/10] powerpc/32: Automatically adapt TASK_SIZE based on constraints

[David Laight <david.laight.linux@gmail.com>]

On Fri, 22 Aug 2025 11:58:05 +0200
Christophe Leroy <christophe.leroy@csgroup.eu> wrote:

> At the time being, TASK_SIZE can be customized by the user via Kconfig
> but it is not possible to check all constraints in Kconfig. Impossible
> setups are detected at compile time with BUILD_BUG() but that leads
> to build failure when setting crazy values. It is not a problem on its
> own because the user will usually either use the default value or set
> a well thought value. However build robots generate crazy random
> configs that lead to build failures, and build robots see it as a
> regression every time a patch adds such a constraint.
> 
> So instead of failing the build when the custom TASK_SIZE is too
> big, just adjust it to the maximum possible value matching the setup.
> 
> Several architectures already calculate TASK_SIZE based on other
> parameters and options.
> 
> In order to do so, move MODULES_VADDR calculation into task_size_32.h
> and ensure that:
> - On book3s/32, userspace and module area have their own segments (256M)
> - On 8xx, userspace has its own full PGDIR entries (4M)
> 
> Then TASK_SIZE is garantied to be correct so remove related
                    ^ guaranteed

> BUILD_BUG()s.