linux-kernel - Re: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations

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Message-ID: <20190509092738.GK2650@hirez.programming.kicks-ass.net>
Date:   Thu, 9 May 2019 11:27:38 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Nicolai Stange <nstange@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        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>,
        Joerg Roedel <jroedel@...e.de>, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations

On Thu, May 09, 2019 at 10:14:31AM +0200, Peter Zijlstra wrote:
> struct ftrace_regs_stack {
> 	ftrace_func_t func;
> 	unsigned long parent_ip;
> };
> 
> void ftrace_regs_handler(struct pr_regs *regs)
> {
> 	struct ftrace_regs_stack *st = (void *)regs->sp;
> 	ftrace_func_t func = st->func;
> 
> 	regs->sp += sizeof(long); /* pop func */
> 
> 	func(regs->ip, st->parent_ip, function_trace_op, regs);
> }

Alternatively we can add things like:

static inline unsigned long int3_emulate_pop(struct pt_regs *regs)
{
	unsigned long val = *(unsigned long *)regs->sp;
	regs->sp += sizeof(unsigned long);
	return val;
}

And do:

	ftrace_func_t func = (void *)int3_emulate_pop(regs);