[PATCH 1/5] powerpc/asm: Add a patch_site macro & helpers for patching instructions

[Michael Ellerman]

Christophe LEROY <christophe.leroy at c-s.fr> writes:
> Le 08/08/2018 à 18:30, Christophe LEROY a écrit :
>> Le 23/07/2018 à 17:07, Michael Ellerman a écrit :
...
>>> diff --git a/arch/powerpc/include/asm/code-patching.h 
>>> b/arch/powerpc/include/asm/code-patching.h
>>> index 812535f40124..b2051234ada8 100644
>>> --- a/arch/powerpc/include/asm/code-patching.h
>>> +++ b/arch/powerpc/include/asm/code-patching.h
>>> @@ -32,6 +32,8 @@ unsigned int create_cond_branch(const unsigned int 
>>> *addr,
>>>   int patch_branch(unsigned int *addr, unsigned long target, int flags);
>>>   int patch_instruction(unsigned int *addr, unsigned int instr);
>>>   int raw_patch_instruction(unsigned int *addr, unsigned int instr);
>>> +int patch_instruction_site(s32 *addr, unsigned int instr);
>>> +int patch_branch_site(s32 *site, unsigned long target, int flags);
>> 
>> Why use s32* instead of unsigned int* as usual for pointer to code ?
>
> Forget my stupid question, I didn't see it was a relative address and 
> not an absolute one.

No worries. 

It is a bit non-obvious at first glance, it looks like the s32 * points
to the instruction. But it points to the s32 that holds the relative
offset from itself, of the instruction.

We could add a typedef to try and make that more obvious, but I
generally don't like typedefs that hide pointerness.

cheers