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Date: Tue, 16 Jan 2018 16:20:41 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: David Woodhouse <dwmw2@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Cc: linux-kernel@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>
Subject: Re: [PATCH v2 10/10] objtool: More complex static jump implementation
Message-ID: <20180116152041.GE2228@hirez.programming.kicks-ass.net>
References: <20180116142825.376986833@infradead.org>
 <20180116143241.478561014@infradead.org>
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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;
> +}