From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 D9E424502F; Mon, 21 Jul 2025 12:48:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753102089; cv=none; b=E8jZoPuVMg3Fp8eB1JExRdlxpUXTxuyaHxIVIDqfiW1CnTqRG7QkKUnTN7AwmtWQTfvIh3DHlGy0G/ojCya/Yc2/lTCjfQgahjwWT41RMTZNNiR5xC9xuOpyFcKRS4dnHEf72GjmTsfDQcK6QtLQCxnW1/FEfqH3Ns72O2GwfWc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753102089; c=relaxed/simple; bh=fhUrUAac/iSii6E8bCY5/2OzAP/25KtTiniEKeJQXGA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=PdSKdNjtBboMgd832HDbP+uXPaRLqk5gH43+jq8vlM1Hc4dWSbJ50xkdj0WNZbdnrejhlZFh0alyVYXwTE1HxqaXdlipy/qcX255Zo/Sd8XhRxZIm5OMID6J0an5xZ63VZTx10Wb++nILTSxyC0qtE01UAmwtUiiRLoJ/+c1UNo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=R8evXuR+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="R8evXuR+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E2550C4CEED; Mon, 21 Jul 2025 12:47:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753102088; bh=fhUrUAac/iSii6E8bCY5/2OzAP/25KtTiniEKeJQXGA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=R8evXuR+wAan3GKqOPc31OKb0HXwT1fcr9RAvjn3iXq9AafrC9dr+uhqKKHXhydc/ ommMgMhlPSa10h8tXea70KugAvoZCogNM+Xt21kS9UmsttjWDnOELNHjux+Ju59MNY /URVoorMncYyCzvX9VeofQFk7WldoN/Ri5qk6rB1XFXfi+hA14lKHW1R2sRPlxfo/E LGLDW2D8KsMU/Gla3tq/bXrtgsgK9NPEPhMAYMtEgjB4rEKVqgNW9ZLANwHmFPzbv2 KyzNMpjT5XzFw+NFZx3vex8f/0R9leYdi3PuQeMO27/gBBOFaJYqsNHIsKj7h+b3pJ 6c41KggZR4CKg== Date: Mon, 21 Jul 2025 13:47:55 +0100 From: Will Deacon To: Ard Biesheuvel Cc: Kees Cook , Mike Rapoport , Arnd Bergmann , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Paolo Bonzini , Vitaly Kuznetsov , Henrique de Moraes Holschuh , Hans de Goede , Ilpo =?iso-8859-1?Q?J=E4rvinen?= , "Rafael J. Wysocki" , Len Brown , Masami Hiramatsu , Michal Wilczynski , Juergen Gross , Andy Shevchenko , "Kirill A. Shutemov" , Roger Pau Monne , David Woodhouse , Usama Arif , "Guilherme G. Piccoli" , Thomas Huth , Brian Gerst , kvm@vger.kernel.org, ibm-acpi-devel@lists.sourceforge.net, platform-driver-x86@vger.kernel.org, linux-acpi@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-efi@vger.kernel.org, linux-mm@kvack.org, Ingo Molnar , "Gustavo A. R. Silva" , Christoph Hellwig , Andrey Konovalov , Andrey Ryabinin , Masahiro Yamada , Nathan Chancellor , Nicolas Schier , Nick Desaulniers , Bill Wendling , Justin Stitt , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-doc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org, sparclinux@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [PATCH v3 04/13] x86: Handle KCOV __init vs inline mismatches Message-ID: References: <20250717231756.make.423-kees@kernel.org> <20250717232519.2984886-4-kees@kernel.org> <202507181541.B8CFAC7E@keescook> Precedence: bulk X-Mailing-List: linux-trace-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 Sun, Jul 20, 2025 at 04:10:01PM +1000, Ard Biesheuvel wrote: > On Sat, 19 Jul 2025 at 08:51, Kees Cook wrote: > > On Fri, Jul 18, 2025 at 11:36:32AM +0300, Mike Rapoport wrote: > > > On Thu, Jul 17, 2025 at 04:25:09PM -0700, Kees Cook wrote: > > > > When KCOV is enabled all functions get instrumented, unless the > > > > __no_sanitize_coverage attribute is used. To prepare for > > > > __no_sanitize_coverage being applied to __init functions, we have to > > > > handle differences in how GCC's inline optimizations get resolved. For > > > > x86 this means forcing several functions to be inline with > > > > __always_inline. > > > > > > > > Signed-off-by: Kees Cook > > > > > > ... > > > > > > > diff --git a/include/linux/memblock.h b/include/linux/memblock.h > > > > index bb19a2534224..b96746376e17 100644 > > > > --- a/include/linux/memblock.h > > > > +++ b/include/linux/memblock.h > > > > @@ -463,7 +463,7 @@ static inline void *memblock_alloc_raw(phys_addr_t size, > > > > NUMA_NO_NODE); > > > > } > > > > > > > > -static inline void *memblock_alloc_from(phys_addr_t size, > > > > +static __always_inline void *memblock_alloc_from(phys_addr_t size, > > > > phys_addr_t align, > > > > phys_addr_t min_addr) > > > > > > I'm curious why from all memblock_alloc* wrappers this is the only one that > > > needs to be __always_inline? > > > > Thread-merge[1], adding Will Deacon, who was kind of asking the same > > question. > > > > Based on what I can tell, GCC has kind of fragile inlining logic, in the > > sense that it can change whether or not it inlines something based on > > optimizations. It looks like the kcov instrumentation being added (or in > > this case, removed) from a function changes the optimization results, > > and some functions marked "inline" are _not_ inlined. In that case, we end up > > with __init code calling a function not marked __init, and we get the > > build warnings I'm trying to eliminate. Got it, thanks for the explanation! > > So, to Will's comment, yes, the problem is somewhat fragile (though > > using either __always_inline or __init will deterministically solve it). > > We've tripped over this before with GCC and the solution has usually > > been to just use __always_inline and move on. > > > > Given that 'inline' is already a macro in the kernel, could we just > add __attribute__((__always_inline__)) to it when KCOV is enabled? That sounds like a more robust approach and, by the sounds of it, we could predicate it on GCC too. That would also provide a neat place for a comment describing the problem. Kees, would that work for you? Will