linux-kernel - Re: [PATCH 3/4] x86/ftrace: make ftrace_int3

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Date:   Mon, 29 Apr 2019 14:52:50 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Nicolai Stange <nstange@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Juergen Gross <jgross@...e.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Andy Lutomirski <luto@...nel.org>,
        Joerg Roedel <jroedel@...e.de>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        live-patching@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH 3/4] x86/ftrace: make ftrace_int3_handler() not to skip
 fops invocation

On Mon, 29 Apr 2019 11:06:58 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> +void replace_call(void *addr, const void *opcode, size_t len, void *target)
> +{
> +	bp_int3_call_target = target;
> +	bp_int3_call_return = addr + len;
> +	bp_int3_handler_irqoff = emulate_call_irqoff;
> +	text_poke_bp(addr, opcode, len, emulate_call_irqon);
> +}

Note, the function tracer does not use text poke. It does it in batch
mode. It can update over 40,000 calls in one go:

	add int3 breakpoint to all 40,000 call sites.
	sync()
	change the last four bytes of each of those call sites
	sync()
	remove int3 from the 40,000 call site with new call.

It's a bit more intrusive than the static call updates we were
discussing before.

-- Steve