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SubjectRe: [PATCH v3 2/2] ARM: ftrace: Add MODULE_PLTS support
On 9 March 2018 at 08:54, Alexander Sverdlin
<alexander.sverdlin@nokia.com> wrote:
> Hello Ard!
>
> On 09/03/18 09:50, Ard Biesheuvel wrote:
>>> +static u32 fixed_plts[] = {
>>> + FTRACE_ADDR,
>>> + MCOUNT_ADDR,
>>> +#ifdef CONFIG_OLD_MCOUNT
>>> + (unsigned long)ftrace_caller_old,
>>> + (unsigned long)mcount,
>>> +#endif
>>> +};
>>> +
>> Do we need this stuff in the PLT loader if ftrace is disabled?
>
> You are right, it probably would not even build w/o FTRACE.
> I'll fix it, thanks for looking into this!
>

Also, perhaps you can make the array const (after you put #ifdef's
around all entries)

>>> static bool in_init(const struct module *mod, unsigned long loc)
>>> {
>>> return loc - (u32)mod->init_layout.base < mod->init_layout.size;
>>> @@ -31,26 +41,43 @@ 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;
>>> + int idx;
>>> + struct plt_entries *plt;
>>> +
>>> + /* Pre-allocate entries in the first plt */
>>> + if (!pltsec->plt_count) {
>>> + plt = (struct plt_entries *)pltsec->plt->sh_addr;
>>> + for (idx = 0; idx < ARRAY_SIZE(plt->ldr); ++idx)
>>> + plt->ldr[idx] = PLT_ENT_LDR;
>>> + memcpy(plt->lit, fixed_plts, sizeof(fixed_plts));
>>> + pltsec->plt_count = ARRAY_SIZE(fixed_plts);
>>> + /*
>>> + * cache the address,
>>> + * ELF header is available only during module load
>>> + */
>>> + pltsec->plt_ent = plt;
>>> + }
>>> + plt = pltsec->plt_ent;
>>>
>>> - struct plt_entries *plt = (struct plt_entries *)pltsec->plt->sh_addr;
>>> - int idx = 0;
>>> + idx = ARRAY_SIZE(fixed_plts);
>>> + while (idx)
>>> + if (plt->lit[--idx] == val)
>>> + return (u32)&plt->ldr[idx];
>>>

... and put all this handling in a helper function that only gets
called if ARRAY_SIZE() > 0

AFAICT, that should allow you to leave the rest unchanged.

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