linux-kernel - Re: [PATCH] objtool: Deal with relative jump tables correctly

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Message-ID: <20241008174201.b23zrrvqv26ihq4t@treble>
Date: Tue, 8 Oct 2024 10:42:01 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] objtool: Deal with relative jump tables correctly

On Tue, Oct 08, 2024 at 12:47:48AM +0200, Ard Biesheuvel wrote:
> -	/*
> -	 * Use of RIP-relative switch jumps is quite rare, and
> -	 * indicates a rare GCC quirk/bug which can leave dead
> -	 * code behind.
> -	 */
> -	if (reloc_type(text_reloc) == R_X86_64_PC32)
> -		file->ignore_unreachables = true;
> -

I'm not sure if this bug still exists on current GCC versions.  If so,
it will start reporting "unreachable instruction" warnings again and
we'll have to figure out a way to resolve that.

Otherwise the patch looks ok.

-- 
Josh