linux-kernel - Re: [PATCH v3 2/2] ARM: ftrace: Add MODULE

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Date:   Fri, 9 Mar 2018 09:54:48 +0100
From:   Alexander Sverdlin <alexander.sverdlin@...ia.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
CC:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH v3 2/2] ARM: ftrace: Add MODULE_PLTS support

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!

>>  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];
>>
> Same here.

-- 
Best regards,
Alexander Sverdlin.