From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AF6CB36E460; Wed, 6 May 2026 07:12:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778051578; cv=none; b=AMgQ5ZJfQ++LPSt8C9wM9/yOT/D++9lWF0cRwEJv0wujm2w3u1bhs4gCGAodnnfnFPkd145r+lsI58Vi6udaY4W42GKDmIXqIcdpDTWgHO+TB100Qw9N+D4odDfwz8o/CQw9AXPXYBw9TIkD8Wvvk2nexNcW0+7XGKPaDzKT/uM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778051578; c=relaxed/simple; bh=ckgl5FC++LQkxsEuWHsMEQzZ3zl/leQjXP4KZ/u7DFs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Y3WyVQga9LiBtJezGRO1o0Xw31akou7r+3Hsf2wHiwSHIC8Z5mP0tQ+swITNdDzvG/GXA2tIvyiJ2QuYm1Fj8zIGDsNLGhVHU59dd2fMrIZQftccHH5AyR69YZoe6sIlff2mTOLbv1okJsa0I7Xiy0Q5KA6YR0oiGnOxhpuM44k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=M+uwskEF; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="M+uwskEF" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=fMovDlk88JtntvXu/seZ66F90g7SFyxentqAJGuZSZY=; b=M+uwskEFSiaSfENlDe8KMqTC1m z/xTI76HSzdMfAX6DI7dyOyOndAEg5QHoBeIMOaMO9cKEx+A0yexAvUqVMPQ6LaVh1ixCTd3VkwrD 2ID0X0crB5mrQWMV92h9j81QWloJomAuUhm2dSGngaFraGXKjLCH2dr9F+kDoqaW7XJ8U52yFOxCu qqrNUFrWAzJe7t8o8x3wMVBKgaLiLTLb3OjFuEyY0GwYZwE6oFQtkTMdw3mQkLWmIZq5axoigcXa1 /o9icvzx3RrpaKhSFcUlVqbzDu9pId82D19w37tpX91ULPxcpy2Fqy5qvnWZi8MqfsRV5AgTx0Yy/ LQDoOjeg==; Received: from 2001-1c00-8d85-4b00-266e-96ff-fe07-7dcc.cable.dynamic.v6.ziggo.nl ([2001:1c00:8d85:4b00:266e:96ff:fe07:7dcc] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wKWEk-00000000jO3-2Yoc; Wed, 06 May 2026 07:00:23 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id DE881302EC2; Wed, 06 May 2026 09:00:00 +0200 (CEST) Date: Wed, 6 May 2026 09:00:00 +0200 From: Peter Zijlstra To: Segher Boessenkool Cc: Sathvika Vasireddy , nathan@kernel.org, nsc@kernel.org, maddy@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com, chleroy@kernel.org, jpoimboe@kernel.org, ojeda@kernel.org, masahiroy@kernel.org, lossin@kernel.org, tamird@kernel.org, thomas.weissschuh@linutronix.de, rostedt@goodmis.org, ihor.solodrai@linux.dev, thuth@redhat.com, pmladek@suse.com, aliceryhl@google.com, elver@google.com, kees@kernel.org, legion@kernel.org, ardb@kernel.org, yuxuan.zuo@outlook.com, alexghiti@rivosinc.com, alexandre.chartre@oracle.com, bp@alien8.de, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v1 1/6] objtool/powerpc: Add build-time fixup of alternate feature branch targets Message-ID: <20260506070000.GZ3126523@noisy.programming.kicks-ass.net> References: <20260505084628.17940-1-sv@linux.ibm.com> <20260505084628.17940-2-sv@linux.ibm.com> <20260505144539.GX3126523@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, May 05, 2026 at 10:56:58AM -0500, Segher Boessenkool wrote: > Hi! > > On Tue, May 05, 2026 at 04:45:39PM +0200, Peter Zijlstra wrote: > > On Tue, May 05, 2026 at 02:16:23PM +0530, Sathvika Vasireddy wrote: > > > switch (opcode) { > > > + case 16: > > > > Like case 18 below, this wants a comment describing which instruction > > this is; bclr ? > > Yes. It is 19/16, b[c]lr (primary opcode 19, secondary opcode 16). > > Where is it described what INSN_RETURN actually means for objtool? Not > in the header file :-( Yeah, nowhere much I'm afraid, it is very much organic growth that is firmly rooted in x86. RETURN, along with sibling/tail CALLs validate things like the stack frame being in identical state as on function entry and a few other sanity checks (DF flag not set, no uaccess). There is also a pile of hacks around the whole return thunk mitigation thing. But that might be less relevant for other archs.