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 042677F
	for <llvm@lists.linux.dev>; Mon,  2 May 2022 07:46:57 +0000 (UTC)
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=pOoEoq3uxOd2hY3qnCRK9aDXRSIdbU9S375EHmEixg8=; b=Zx1qMADDPH8oEOTa4jVupxWl6E
	jp0Ix1UpwVxb/Fun8uQkpi/VDVUrELD+eS/RX9VUTmUff5Lfk9pHLGnzXGRo5XQjnKpVQAnDGA+HY
	6njW7JD42U9XDnB6D3TI9rmTZ/aqSpbsxfUtPIHKH48smGoBc+hsJpqXaRadtuEJcHvW3GiOXvq13
	d4zs632v/3gKbbrqz0yWyBW7gjlr+57/KxIGorr/dnptiwV1AYALOr2y65wpMHAAJ4xsSV0n37yzE
	19MxrkmlClL3jeLhLETg9bIIv0pjGFEOLCYtKCiGSpok8qhV9B6cU0FBm//Y4T/y5l5jfkXJiDpIU
	UHe+W3Jw==;
Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net)
	by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux))
	id 1nlQlP-00AOnG-Mt; Mon, 02 May 2022 07:46:36 +0000
Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000)
	id 4FA2398035B; Mon,  2 May 2022 09:46:33 +0200 (CEST)
Date: Mon, 2 May 2022 09:46:33 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Sami Tolvanen <samitolvanen@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Kees Cook <keescook@chromium.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>, X86 ML <x86@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Mark Rutland <mark.rutland@arm.com>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Joao Moreira <joao@overdrivepizza.com>,
	Sedat Dilek <sedat.dilek@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	linux-hardening@vger.kernel.org,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	llvm@lists.linux.dev
Subject: Re: [RFC PATCH 14/21] treewide: static_call: Pass call arguments to
 the macro
Message-ID: <20220502074633.GA479834@worktop.programming.kicks-ass.net>
References: <20220429203644.2868448-1-samitolvanen@google.com>
 <20220429203644.2868448-15-samitolvanen@google.com>
 <Ymxy/CU+tZhQ9UtN@hirez.programming.kicks-ass.net>
 <CABCJKud8vC6RwQLs2YXnZMZaXGNYBEq+sNmOsgGjjAw4MfuZuw@mail.gmail.com>
Precedence: bulk
X-Mailing-List: llvm@lists.linux.dev
List-Id: <llvm.lists.linux.dev>
List-Subscribe: <mailto:llvm+subscribe@lists.linux.dev>
List-Unsubscribe: <mailto:llvm+unsubscribe@lists.linux.dev>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CABCJKud8vC6RwQLs2YXnZMZaXGNYBEq+sNmOsgGjjAw4MfuZuw@mail.gmail.com>

On Fri, Apr 29, 2022 at 05:49:21PM -0700, Sami Tolvanen wrote:
> On Fri, Apr 29, 2022 at 4:21 PM Peter Zijlstra <peterz@infradead.org> wrote:
> > Can you explain why this is needed? I don't think there are any indirect
> > calls to get confused about. That is, if you have STATIC_CALL_INLINE
> > then the compiler should be emitting direct calls to the trampoline.
> 
> Clang emits an indirect call for ({ &f; })(), which is optimized into
> a direct call when possible. Come to think of it, the recent
> InstCombine change to the compiler patch should solve this issue. Let
> me double check, I'd be more than happy to drop these two patches.

Oooh, but this must not require any magic. That is, we have a *ton* of
code that relies on constant propagation of function pointers to not
emit indirect calls.

Please make sure that 'just-works'.

Look at all the __always_inline functions in rbtree*.h for instance,
some like latch and augment rely on quite complicated const propagation
for the actual function pointer is in a const struct.

I've verified all that actually generates direct calls when we did that
code (on GCC, clang wasn't really a thing back then).