Re: [PATCH v3 4/4] objtool: orc_gen: Move orc_entry out of instruction structure

[Julien Thierry]

On 7/30/20 2:33 PM, peterz@xxxxxxxxxxxxx wrote:
> On Thu, Jul 30, 2020 at 01:40:48PM +0100, Julien Thierry wrote:
> > On 7/30/20 11:03 AM, peterz@xxxxxxxxxxxxx wrote:
> > > On Thu, Jul 30, 2020 at 10:41:43AM +0100, Julien Thierry wrote:
> > > > One orc_entry is associated with each instruction in the object file,
> > > > but having the orc_entry contained by the instruction structure forces
> > > > architectures not implementing the orc subcommands to provide a dummy
> > > > definition of the orc_entry.
>
> > I guess I forgot about the usecase of running objtool on vmlinux...
>
> Right, and LTO builds will even do ORC at that level.
>
> > On a kernel build for x86_64 defconfig, the difference in time seems to be
> > withing the noise.
>
> Good.
>
> > But I agree the proposed code is not ideal and on the other we've tried
> > avoiding #ifdef in the code. Ideally I'd have an empty orc_entry definition
> > when SUBCMD_ORC is not implemented.
> >
> > Would you have a suggested approach to do that?
>
> How ugly is having that:
>
> struct orc_entry { };
>
> ?

Not sure I am understanding the suggestion. Without #ifdef this will 
conflict with the definition in <asm/orc_types.h> for x86. Or every arch 
needs to provide their own <asm/orc_types.h> and definition of struct 
orc_entry, even if they don't implement the orc subcommand.

Which would be preferable? #ifdef? or arch provided definition? (or 
something I have not thought of)

--
Julien Thierry