On 13 March 2018 at 17:32, Alexander Sverdlin
> Hi Ard!
> On 13/03/18 18:18, Ard Biesheuvel wrote:
>>>>> u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
>>>>> struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core
>>>>> + struct plt_entries *plt;
>>>>> + int idx;
>>>>> - struct plt_entries *plt = (struct plt_entries
>>> ^^^^^^^^^^^ (*)
>>>>> - int idx = 0;
>>>>> + /* cache the address, ELF header is available only during module
>>>>> load */
>>>>> + if (!pltsec->plt_ent)
>>>>> + pltsec->plt_ent = (struct plt_entries
>>>>> + plt = pltsec->plt_ent;
>>>> Where is plt_ent ever used?
>>> Above is exactly the place it's used.
>>> I need to cache it because after the module load is finished the ELF header
>>> is freed,
>>> pltsec->plt pointer (*) is not valid any more.
>>> With the above modification it's possible to call the function during the
>>> whole life
>>> time of the module.
>> Right, ok. That's a problem.
>> This means that you are relying on get_module_plt() being called at
>> least once at module load time, which is not guaranteed.
> This is indeed guaranteed. For FTRACE use case. If it's being called from
> FTRACE in
> run time, this would mean there were long calls in this module section, which
> turn means, get_module_plt() was called at least once for this module and this
> This doesn't hold in general, though.
> In any case, if you insist, I can try to rework the whole stuff implementing
I think it would be much better to use the module_finalize() hook for
this, given that it is only called once already, and all the data you
need is still available.
Note that ARM already has such a function, so you'll need to add a
call there, i.e.,
or something like that. The CONFIG_FTRACE dependency can be kept local