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

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Message-ID: <20181005220220.770d9e18@vmware.local.home>
Date:   Fri, 5 Oct 2018 22:02:20 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Matthew Helsley <mhelsley@...are.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jason Baron <jbaron@...mai.com>, Jiri Kosina <jkosina@...e.cz>
Subject: Re: [POC][RFC][PATCH 1/2] jump_function: Addition of new feature
 "jump_function"

On Fri, 05 Oct 2018 21:51:11 -0400
Steven Rostedt <rostedt@...dmis.org> 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" )
> +

Note, the assembler can easily put in a two byte jump here. The .balign
was suppose to also have some padding (nop) incase that happens. It's
fine, because we can just replace it with a 5 byte jump, as long as we
have 3 bytes afterward if it is a two byte jump.

-- Steve