On 9/2/26 10:18 AM, Hao Ge wrote:
> SHF_ALLOC means, per the ELF spec, that a section occupies memory
> during process execution. Some module sections occupy memory
> outside the regular module layout, for example the percpu section
> with its per-CPU allocations. The loader currently excludes such
> a section from the layout by clearing its SHF_ALLOC, which
> overloads the flag with a loader-internal meaning.
> apply_relocations() needs a special case for the section, and
> find_sec(".data..percpu") returns different results before and
> after layout_and_allocate().
>
> Introduce SH_ENTSIZE_STANDALONE to mark sections with a separate
> allocation. The percpu section is its first user. layout_sections()
> and move_module() skip marked sections, and apply_relocations() goes
> back to testing only SHF_ALLOC.
>
> No functional change intended.
>
> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
> Reported-by: Sashiko <[email protected]>
> Based-on-a-patch-by: Petr Pavlu <[email protected]>
> Link:
> https://lore.kernel.org/all/[email protected]/
> Cc: [email protected]
> Signed-off-by: Hao Ge <[email protected]>
> ---
> [...]
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index c32f1d370b73..078dae188aba 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -1618,14 +1618,8 @@ static int apply_relocations(struct module *mod, const
> struct load_info *info)
> if (infosec >= info->hdr->e_shnum)
> continue;
>
> - /*
> - * Don't bother with non-allocated sections.
> - * An exception is the percpu section, which has separate
> allocations
> - * for individual CPUs. We relocate the percpu section in the
> initial
> - * ELF template and subsequently copy it to the per-CPU
> destinations.
> - */
> - if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC) &&
> - (!infosec || infosec != info->index.pcpu))
> + /* Don't bother with non-allocated sections. */
> + if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC))
> continue;
>
> if (info->sechdrs[i].sh_flags & SHF_RELA_LIVEPATCH)
Please keep a comment about how .data..percpu is handled. This is not
obvious and should be described explicitly.
Something like the following:
/*
* Don't bother with non-allocated sections.
*
* Note that .data..percpu has separate allocations for
* individual CPUs. We relocate the section in the
* initial ELF template and subsequently copy it to the
* per-CPU destinations.
*/
--
Thanks,
Petr
