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Date:   Wed, 1 May 2019 21:03:48 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Nicolai Stange <nstange@suse.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Jiri Kosina <jikos@kernel.org>,
        Miroslav Benes <mbenes@suse.cz>,
        Petr Mladek <pmladek@suse.com>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Shuah Khan <shuah@kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Mimi Zohar <zohar@linux.ibm.com>,
        Juergen Gross <jgross@suse.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
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        Masahiro Yamada <yamada.masahiro@socionext.com>,
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Subject: Re: [RFC][PATCH] ftrace/x86: Emulate call function while updating in
 breakpoint handler
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On Wed, May 01, 2019 at 02:58:24PM -0400, Steven Rostedt wrote:
> > +	if (ftrace_location(ip)) {
> > +		int3_emulate_call(regs, ftrace_update_func_call);
> 
> Should be:
> 
> 		int3_emulate_call(regs, (unsigned long)ftrace_regs_caller);

Ah, I lost the plot a little there.

> > +		return 1;
> > +	} else if (is_ftrace_caller(ip)) {
> > +		if (!ftrace_update_func_call) {
> > +			int3_emulate_jmp(regs, regs->ip - INT3_INSN_SIZE + CALL_INSN_SIZE);
> 
> I see what you did here, but I think:
> 
> 			int3_emulate_jmp(regs, ip + CALL_INSN_SIZE);
> 
> looks better. But that said, we could in the beginning do:
> 
> 	ip = regs->ip - INT3_INSN_SIZE;
> 
> instead of
> 
> 	ip = regs->ip - 1;
> 
> I made these updates and posted them to Linus.

I was actually considering:

static inline void int3_emulate_nop(struct pt_regs *regs, unsigned long size)
{
	int3_emulate_jmp(regs, regs->ip - INT3_INSN_SIZE + size);
}

And then the above becomes:

	int3_emulate_nop(regs, CALL_INSN_SIZE);

Hmm?