linux-kernel - Re: [PATCH 6/9] LoongArch: modules/ftrace: Initialize PLT at load time

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Date:   Sat, 20 Aug 2022 09:30:52 +0800
From:   Qing Zhang <zhangqing@...ngson.cn>
To:     Jinyang He <hejinyang@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH 6/9] LoongArch: modules/ftrace: Initialize PLT at load
 time



On 2022/8/19 下午6:43, Jinyang He wrote:
> On 2022/8/19 16:16, Qing Zhang wrote:
> 
>> To Implement ftrace trampiones through plt entry.
>>
>> Tested by forcing ftrace_make_call() to use the module PLT, and then
>> loading up a module after setting up ftrace with:
>>
>> | echo ":mod:<module-name>" > set_ftrace_filter;
>> | echo function > current_tracer;
>> | modprobe <module-name>
>>
>> Since FTRACE_ADDR/FTRACE_REGS_ADDR is only defined when 
>> CONFIG_DYNAMIC_FTRACE
>> is selected, we wrap its use along with most of 
>> module_init_ftrace_plt() with
>> ifdeffery rather than using IS_ENABLED().
>>
>> Signed-off-by: Qing Zhang <zhangqing@...ngson.cn>
>> ---
>>   arch/loongarch/include/asm/ftrace.h     |  4 ++
>>   arch/loongarch/include/asm/inst.h       |  2 +
>>   arch/loongarch/include/asm/module.h     | 14 +++--
>>   arch/loongarch/include/asm/module.lds.h |  1 +
>>   arch/loongarch/kernel/ftrace_dyn.c      | 79 +++++++++++++++++++++++++
>>   arch/loongarch/kernel/inst.c            | 12 ++++
>>   arch/loongarch/kernel/module-sections.c | 11 ++++
>>   arch/loongarch/kernel/module.c          | 48 +++++++++++++++
>>   8 files changed, 166 insertions(+), 5 deletions(-)
> [...]
>> @@ -36,14 +39,15 @@ Elf_Addr module_emit_plt_entry(struct module *mod, 
>> unsigned long val);
>>   static inline struct plt_entry emit_plt_entry(unsigned long val)
>>   {
>> -    u32 lu12iw, lu32id, lu52id, jirl;
>> +    u32 addu16id, lu32id, lu52id, jirl;
>> -    lu12iw = (lu12iw_op << 25 | (((val >> 12) & 0xfffff) << 5) | 
>> LOONGARCH_GPR_T1);
>> +    addu16id = larch_insn_gen_addu16id(LOONGARCH_GPR_T1, 
>> LOONGARCH_GPR_ZERO,
>> +        ADDR_IMM(val, ADDU16ID));
> 
> Hi, Qing,
> 
> Why change lu12iw to addu16id? They have same effect here.
> 
Hi. Jinyang

Yes, the effect is the same.
I will modify it to lu12iw in V2, which can be consistent with the 
user's plt style.

Thanks,
- Qing

> 
>>       lu32id = larch_insn_gen_lu32id(LOONGARCH_GPR_T1, ADDR_IMM(val, 
>> LU32ID));
>>       lu52id = larch_insn_gen_lu52id(LOONGARCH_GPR_T1, 
>> LOONGARCH_GPR_T1, ADDR_IMM(val, LU52ID));
>> -    jirl = larch_insn_gen_jirl(0, LOONGARCH_GPR_T1, 0, (val & 0xfff));
>> +    jirl = larch_insn_gen_jirl(0, LOONGARCH_GPR_T1, 0, (val & 0xffff));
>> -    return (struct plt_entry) { lu12iw, lu32id, lu52id, jirl };
>> +    return (struct plt_entry) { addu16id, lu32id, lu52id, jirl };
>>   }
> [...]
>> +static int module_init_ftrace_plt(const Elf_Ehdr *hdr, const Elf_Shdr 
>> *sechdrs,
>> +                  struct module *mod)
>> +{
>> +#ifdef CONFIG_DYNAMIC_FTRACE
>> +    const Elf_Shdr *s;
>> +    struct plt_entry *ftrace_plts;
>> +
>> +    s = find_section(hdr, sechdrs, ".ftrace_trampoline");
>> +    if (!s)
>> +        return -ENOEXEC;
> 
> Return value is not used later, may we do something or drop returning 
> value.
> 
Yes, Should return module_init_ftrace_plt(hdr, sechdrs, mod) here.

Thanks,
-Qing
> Thanks,
> 
> Jinyang
> 
>> +
>> +    ftrace_plts = (void *)s->sh_addr;
>> +
>> +    ftrace_plts[FTRACE_PLT_IDX] = emit_plt_entry(FTRACE_ADDR);
>> +
>> +    if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
>> +        ftrace_plts[FTRACE_REGS_PLT_IDX] = 
>> emit_plt_entry(FTRACE_REGS_ADDR);
>> +
>> +    mod->arch.ftrace_trampolines = ftrace_plts;
>> +#endif
>> +    return 0;
>> +}
>> +
>> +int module_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs, 
>> struct module *mod)
>> +{
>> +    module_init_ftrace_plt(hdr, sechdrs, mod);
>> +
>> +    return 0;
>> +}
>