Re: [PATCH v2 5/5] powerpc64/ftrace: Implement support for ftrace_regs_caller()

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

Steven Rostedt wrote:
> On Wed, 21 Mar 2018 16:13:22 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
>=20
>>  int module_finalize_ftrace(struct module *mod, const Elf_Shdr *sechdrs)
>>  {
>>  	mod->arch.toc =3D my_r2(sechdrs, mod);
>> -	mod->arch.tramp =3D create_ftrace_stub(sechdrs, mod);
>> +	mod->arch.tramp =3D create_ftrace_stub(sechdrs, mod,
>> +					(unsigned long)ftrace_caller);
>> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>> +	mod->arch.tramp_regs =3D create_ftrace_stub(sechdrs, mod,
>> +					(unsigned long)ftrace_regs_caller);
>=20
> So you only reference ftrace_regs_caller if you have
> DYNAMIC_FTRACE_WITH_REGS defined?

Yes.

>=20
>> +	if (!mod->arch.tramp_regs)
>> +		return -ENOENT;
>> +#endif
>> =20
>>  	if (!mod->arch.tramp)
>>  		return -ENOENT;
>=20
>=20
>> diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/power=
pc/kernel/trace/ftrace_64_mprofile.S
>> index 8f2380304ef1..7b81db85f76e 100644
>> --- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
>> +++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
>> @@ -20,8 +20,8 @@
>>  #ifdef CONFIG_DYNAMIC_FTRACE
>>  /*
>>   *
>> - * ftrace_caller() is the function that replaces _mcount() when ftrace =
is
>> - * active.
>> + * ftrace_caller()/ftrace_regs_caller() is the function that replaces _=
mcount()
>> + * when ftrace is active.
>>   *
>>   * We arrive here after a function A calls function B, and we are the t=
race
>>   * function for B. When we enter r1 points to A's stack frame, B has no=
t yet
>> @@ -37,7 +37,7 @@
>>   * Our job is to save the register state into a struct pt_regs (on the =
stack)
>>   * and then arrange for the ftrace function to be called.
>>   */
>=20
> Perhaps you want to add:
>=20
> #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>=20
> here.

I think that will always be set here. ftrace_64_mprofile.S is only built=20
for -mprofile-kernel and we select HAVE_DYNAMIC_FTRACE_WITH_REGS if=20
MPROFILE_KERNEL is enabled. It looks like there is no way to unset just=20
CONFIG_DYNAMIC_FTRACE_WITH_REGS and so, for -mprofile-kernel, we can=20
assume it is always set?

- Naveen

=