Re: [POC][RFC][PATCH 1/2] jump_function: Addition of new feature "jump_function"

[Peter Zijlstra]

On Sat, Oct 06, 2018 at 09:39:05AM -0400, Steven Rostedt wrote:
> On Sat, 6 Oct 2018 14:12:11 +0200
> Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> > On Fri, Oct 05, 2018 at 09:51:11PM -0400, Steven Rostedt wrote:
> > > +#define arch_dynfunc_trampoline(name, def)	\
> > > +	asm volatile (				\
> > > +	".globl dynfunc_" #name "; \n\t"	\
> > > +	"dynfunc_" #name ": \n\t"		\
> > > +	"jmp " #def " \n\t"			\
> > > +	".balign 8 \n \t"			\
> > > +	: : : "memory" )  
> > 
> > Bah, what is it with you people and trampolines. Why can't we, just like
> > jump_label, patch the call directly?
> > 
> > The whole call+jmp thing is silly, don't do that. It just wrecks I$ and
> > is slower for no real reason afaict.
> 
> My first attempt was to do just that. But to add a label at the
> call site required handling all the parameters too. See my branch:
>  ftrace/jump_function-v1 for how ugly it got (and it didn't work).

Can't we hijack the relocation records for these functions before they
get thrown out in the (final) link pass or something?