On 9/8/26 11:24 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. Based on a patch by Petr Pavlu [1].
>
> .data..percpu keeps SHF_ALLOC, so it would now show up under
> /sys/module/*/sections/. The section has one instance per CPU and no
> single address to report, and the entry never existed before, so
> skip it in add_sect_attrs(). add_notes_attrs() indexes its attrs[]
> array and skips it too. No functional change otherwise.
>
> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
> Reported-by: Sashiko <[email protected]>
> Link:
> https://lore.kernel.org/all/[email protected]/ [1]
> Suggested-by: Petr Pavlu <[email protected]>
> Cc: [email protected]
> Signed-off-by: Hao Ge <[email protected]>
> ---
> [...]
> diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
> index 0fc11e45df9b..49190deae61e 100644
> --- a/kernel/module/kallsyms.c
> +++ b/kernel/module/kallsyms.c
> @@ -76,7 +76,7 @@ static char elf_type(const Elf_Sym *sym, const struct
> load_info *info)
> }
>
> static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs,
> - unsigned int shnum, unsigned int pcpundx)
> + unsigned int shnum)
> {
> const Elf_Shdr *sec;
> enum mod_mem_type type;
> @@ -86,11 +86,6 @@ static bool is_core_symbol(const Elf_Sym *src, const
> Elf_Shdr *sechdrs,
> !src->st_name)
> return false;
>
> -#ifdef CONFIG_KALLSYMS_ALL
> - if (src->st_shndx == pcpundx)
> - return true;
> -#endif
> -
> sec = sechdrs + src->st_shndx;
> type = sec->sh_entsize >> SH_ENTSIZE_TYPE_SHIFT;
> if (!(sec->sh_flags & SHF_ALLOC)
> @@ -131,8 +126,7 @@ void layout_symtab(struct module *mod, struct load_info
> *info)
> /* Compute total space required for the core symbols' strtab. */
> for (ndst = i = 0; i < nsrc; i++) {
> if (i == 0 || is_livepatch_module(mod) ||
> - is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum,
> - info->index.pcpu)) {
> + is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum))
> {
> strtab_size += strlen(&info->strtab[src[i].st_name]) +
> 1;
> ndst++;
> }
> @@ -199,8 +193,7 @@ void add_kallsyms(struct module *mod, const struct
> load_info *info)
> for (ndst = i = 0; i < kallsyms->num_symtab; i++) {
> kallsyms->typetab[i] = elf_type(src + i, info);
> if (i == 0 || is_livepatch_module(mod) ||
> - is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum,
> - info->index.pcpu)) {
> + is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum))
> {
> ssize_t ret;
>
> mod->core_kallsyms.typetab[ndst] =
FTR These changes in kernel/module/kallsyms.c have a conflict with the
series "Ignore local labels and mapping symbols during module load" [1],
which is currently queued on modules-next, but it should be
straightforward to resolve.
> diff --git a/kernel/module/sysfs.c b/kernel/module/sysfs.c
> index 01c65d608873..f64170344e69 100644
> --- a/kernel/module/sysfs.c
> +++ b/kernel/module/sysfs.c
> @@ -62,6 +62,15 @@ static void free_sect_attrs(struct module_sect_attrs
> *sect_attrs)
> kfree(sect_attrs);
> }
>
> +/*
> + * .data..percpu has a separate allocation per CPU and no single
> + * address to report.
> + */
> +static bool sect_visible(const struct load_info *info, unsigned int i)
> +{
> + return !sect_empty(&info->sechdrs[i]) && i != info->index.pcpu;
> +}
> +
> static int add_sect_attrs(struct module *mod, const struct load_info *info)
> {
> struct module_sect_attrs *sect_attrs;
> @@ -72,7 +81,7 @@ static int add_sect_attrs(struct module *mod, const struct
> load_info *info)
>
> /* Count loaded sections and allocate structures */
> for (i = 0; i < info->hdr->e_shnum; i++)
> - if (!sect_empty(&info->sechdrs[i]))
> + if (sect_visible(info, i))
> nloaded++;
> sect_attrs = kzalloc_flex(*sect_attrs, attrs, nloaded);
> if (!sect_attrs)
> @@ -92,7 +101,7 @@ static int add_sect_attrs(struct module *mod, const struct
> load_info *info)
> for (i = 0; i < info->hdr->e_shnum; i++) {
> Elf_Shdr *sec = &info->sechdrs[i];
>
> - if (sect_empty(sec))
> + if (!sect_visible(info, i))
> continue;
> sysfs_bin_attr_init(sattr);
> sattr->attr.name =
> @@ -181,7 +190,7 @@ static int add_notes_attrs(struct module *mod, const
> struct load_info *info)
>
> nattr = ¬es_attrs->attrs[0];
> for (loaded = i = 0; i < info->hdr->e_shnum; ++i) {
> - if (sect_empty(&info->sechdrs[i]))
> + if (!sect_visible(info, i))
> continue;
> if (info->sechdrs[i].sh_type == SHT_NOTE) {
> sysfs_bin_attr_init(nattr);
add_notes_attrs() has two sect_empty() calls. Both should be changed to
sect_visible().
With this fixed, the patch looks ok to me. Feel free to add:
Reviewed-by: Petr Pavlu <[email protected]>
[1]
https://lore.kernel.org/linux-modules/[email protected]/
--
Thanks,
Petr
