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SubjectRe: [PATCH 1/2] module: Overwrite st_size instead of st_info
On Mon, Nov 19, 2018 at 05:25:12PM +0100, Vincent Whitchurch wrote:
> st_info is currently overwritten after relocation and used to store the
> elf_type(). However, we're going to need it fix kallsyms on ARM's
> Thumb-2 kernels, so preserve st_info and overwrite the st_size field
> instead. st_size is neither used by the module core nor by any
> architecture.
>
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
> ---
> v4: Split out to separate patch. Use st_size instead of st_other.
> v1-v3: See PATCH 2/2
>
> kernel/module.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 49a405891587..3d86a38b580c 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2682,7 +2682,7 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
>
> /* Set types up while we still have access to sections. */
> for (i = 0; i < mod->kallsyms->num_symtab; i++)
> - mod->kallsyms->symtab[i].st_info
> + mod->kallsyms->symtab[i].st_size
> = elf_type(&mod->kallsyms->symtab[i], info);
>
> /* Now populate the cut down core kallsyms for after init. */
> @@ -4061,7 +4061,7 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
> kallsyms = rcu_dereference_sched(mod->kallsyms);
> if (symnum < kallsyms->num_symtab) {
> *value = kallsyms->symtab[symnum].st_value;
> - *type = kallsyms->symtab[symnum].st_info;
> + *type = kallsyms->symtab[symnum].st_size;
> strlcpy(name, symname(kallsyms, symnum), KSYM_NAME_LEN);
> strlcpy(module_name, mod->name, MODULE_NAME_LEN);
> *exported = is_exported(name, *value, mod);

Based on the discussion here:

Reviewed-by: Dave Martin <Dave.Martin@arm.com>

(I still think this is a bit gross, but without resorting to overkill
there's not an obvious nicer option. Even before this patch, we were
abusing st_info. Of course, someday somebody may find a use for
st_size and then we'd need to revisit this code...)

Cheers
---Dave

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