Re: [RFC PATCH 1/4] objtool: Add --mnop as an option to --mcount

[Christophe Leroy]

Le 24/05/2022 à 12:15, Naveen N. Rao a écrit :
> Christophe Leroy wrote:
>>
>>
>> Le 23/05/2022 à 19:55, Sathvika Vasireddy a écrit :
>>> Architectures can select HAVE_NOP_MCOUNT if they choose
>>> to nop out mcount call sites. If that config option is
>>> selected, then --mnop is passed as an option to objtool,
>>> along with --mcount.
>>>
>>
>> Is there a reason not to nop out mcount call sites on powerpc as well ?
> 
> Yes, if there are functions that are out of range of _mcount(), then the 
> linker would have inserted long branch trampolines. We detect such cases 
> during boot. But, if we nop out the _mcount call sites during build 
> time, we will need some other way to identify these.
> 

But does it really matter whether _mcount is reachable or not ?

_mcount is never used, and the function we want to call in lieu of 
_mcount might be reachable while _mcount is not or might be unreachable 
while _mcount is.

Christophe