Messages in this thread | | | From | Ard Biesheuvel <> | Date | Tue, 13 Mar 2018 17:39:59 +0000 | Subject | Re: [PATCH v4 2/2] ARM: ftrace: Add MODULE_PLTS support |
| |
On 13 March 2018 at 17:32, Alexander Sverdlin <alexander.sverdlin@nokia.com> wrote: > 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 : >>>>> &mod->arch.init; >>>>> + struct plt_entries *plt; >>>>> + int idx; >>>>> >>>>> - struct plt_entries *plt = (struct plt_entries *)pltsec->plt->sh_addr; >>> ^^^^^^^^^^^ (*) >>> >>>>> - int idx = 0; >>>>> + /* cache the address, ELF header is available only during module load */ >>>>> + if (!pltsec->plt_ent) >>>>> + pltsec->plt_ent = (struct plt_entries *)pltsec->plt->sh_addr; >>>>> + 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 in > turn means, get_module_plt() was called at least once for this module and this > section. > > This doesn't hold in general, though. > > In any case, if you insist, I can try to rework the whole stuff implementing module_finalize(). >
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.,
if (IS_ENABLED(CONFIG_ARM_MODULE_PLTS)) module_plt_alloc_fixed();
or something like that. The CONFIG_FTRACE dependency can be kept local to module-plts.c
| |