Messages in this thread |  | | Subject | Re: [POC][RFC][PATCH 1/2] jump_function: Addition of new feature "jump_function" | From | Andy Lutomirski <> | Date | Sat, 6 Oct 2018 08:13:18 -0700 |
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> On Oct 6, 2018, at 6:39 AM, Steven Rostedt <rostedt@goodmis.org> wrote: > > On Sat, 6 Oct 2018 14:12:11 +0200 > Peter Zijlstra <peterz@infradead.org> 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). > >> >> Steve, also see: >> >> https://lkml.kernel.org/r/20181005081333.15018-1-ard.biesheuvel@linaro.org > > Interesting. I don't have time to look at it at the moment to see what > was done, but will do so in the near future. > > Remember, this was a proof of concept and even with the trampolines, it > showed a great level of improvement. One thought was to do a > "recordmcount.c" type of action to find where the calls were and patch > them directly at boot up. I tried to keep the API the same where this > could actually be done as an improvement later. > > Perhaps a gcc plugin might work too. >
My suggestion was to have objtool do the dirty work. Josh said something suspiciously like “sounds fun” on IRC :)
> I'll have to see what Ard did to handle the function parameters. > > -- Steve >
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