linux-kernel - Re: [PATCH v2 10/10] objtool: More complex static jump implementation

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Message-ID: <20180116152041.GE2228@hirez.programming.kicks-ass.net>
Date:   Tue, 16 Jan 2018 16:20:41 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Woodhouse <dwmw2@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>
Subject: Re: [PATCH v2 10/10] objtool: More complex static jump implementation

On Tue, Jan 16, 2018 at 03:28:35PM +0100, Peter Zijlstra wrote:
> +static int grow_static_blocks(struct objtool_file *file)
> +{
> +	struct instruction *insn;
> +	bool static_block = false;
> +
> +	for_each_insn(file, insn) {
> +		if (!static_block && !insn->static_jump_dest)
> +			continue;
> +
> +		if (insn->static_jump_dest) {
> +			static_block = true;
> +			continue;
> +		}
> +
> +		if (insn->branch_target) {
> +			static_block = false;
> +			continue;
> +		} else switch (insn->type) {
> +		case INSN_JUMP_CONDITIONAL:
> +		case INSN_JUMP_DYNAMIC:

Hmm, I think I also should have added INSN_JUMP_UNCONDITIONAL here,
because the for_each_insn() iteration simply iterates through the entire
file in linear order, it doesn't actually _follow_ the jumps.

So this would result in code after the unconditional jump also being
marked static (although very likely it ends up being a branch target and
thus stops it through that).

/me updates.

> +		case INSN_CALL:
> +		case INSN_CALL_DYNAMIC:
> +		case INSN_RETURN:
> +		case INSN_BUG:
> +			static_block = false;
> +			continue;
> +		}
> +
> +		insn->static_jump_dest = static_block;
> +	}
> +
> +	return 0;
> +}