From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (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 9FC8A21D3EC for ; Thu, 12 Jun 2025 07:58:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749715106; cv=none; b=gACy1kr0OQ2+yddJSZnawSEnbP3R3UbCCEg5SYvOPk40WCIDdZMoAzWz/WQPXvK+qmM1MnRMjicT6opeEq0hPYqtPTfqcU5lCdvDJFT1/AkR/t/ib/u2jdc7B/zV7vcos0uuYj3H6Ch1/Kz27BihxqCFoukucjeqK7WLSVoKqOY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749715106; c=relaxed/simple; bh=m7f6LnCqLuKAy3Gi20gsFjFzCCZMcpkuQ8x0mccGp0w=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=PTUJQnyr244fed40ooMyPw3JL4ArB2sd39aIsLp4stLHC8z0C8sKEczAzjZPzNRC/cvUdtebSafg0zEDQEUogAGlJl2e9URHHxmINU/J271mQzBjM9XV8k1dMIryUEFVAWWdP1avAlrGd8dYHiR3O8Vd6pi+99RR6AzYx0Xj69w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=UPRfnn08; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="UPRfnn08" Received: from [192.168.88.20] (91-158-153-178.elisa-laajakaista.fi [91.158.153.178]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 550F6D6; Thu, 12 Jun 2025 09:58:12 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1749715093; bh=m7f6LnCqLuKAy3Gi20gsFjFzCCZMcpkuQ8x0mccGp0w=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=UPRfnn08AaC2BjPcestxx8Y+JXeyOrA8T1Lw6d1PlwlICAHH1h7h5tf4jxG0SSJBL a9cyY3jEZW2Jh+uxBf/1/QTOC7alxDptmrpQ8jyosOLizhH3/N4bpifa/DcyqHOnT5 TyxB4wTfemNqGJBkYC00hsQ2Op46CqtDi0QUcVRo= Message-ID: Date: Thu, 12 Jun 2025 10:58:17 +0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] drm: omapdrm: reduce clang stack usage To: Arnd Bergmann Cc: Arnd Bergmann , Nick Desaulniers , Bill Wendling , Justin Stitt , "Dr. David Alan Gilbert" , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Nathan Chancellor References: <20250610092737.2641862-1-arnd@kernel.org> Content-Language: en-US From: Tomi Valkeinen Autocrypt: addr=tomi.valkeinen@ideasonboard.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi, On 10/06/2025 12:27, Arnd Bergmann wrote: > From: Arnd Bergmann > > The thread sanitizer makes the stack usage explode from extra variable > spills in dispc_runtime_resume: > > drivers/gpu/drm/omapdrm/dss/dispc.c:4735:27: error: stack frame size (1824) exceeds limit (1280) in 'dispc_runtime_resume' [-Werror,-Wframe-larger-than] > > I could not figure out what exactly is going on here, but I see that > whenever dispc_restore_context() is not inlined, that function > and its caller shrink below 900 bytes combined of stack usage. > > Signed-off-by: Arnd Bergmann > --- > drivers/gpu/drm/omapdrm/dss/dispc.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/omapdrm/dss/dispc.c b/drivers/gpu/drm/omapdrm/dss/dispc.c > index 533f70e8a4a6..cf055815077c 100644 > --- a/drivers/gpu/drm/omapdrm/dss/dispc.c > +++ b/drivers/gpu/drm/omapdrm/dss/dispc.c > @@ -524,7 +524,7 @@ static void dispc_save_context(struct dispc_device *dispc) > DSSDBG("context saved\n"); > } > > -static void dispc_restore_context(struct dispc_device *dispc) > +static noinline_for_stack void dispc_restore_context(struct dispc_device *dispc) > { > int i, j; > While I don't think this causes any harm, but... What's going on here? If I compile with gcc (x86 or arm), I see stack usage in few hundreds of bytes. If I compile with LLVM=1, the stack usage jumps to over a thousand. Is clang just broken? I don't see anything special with dispc_restore_context() or dispc_runtime_resume(), so is this same thing happening all around the kernel, and we need to sprinkle noinlines everywhere? Or do we get some extra debugging feature enabled only on clang with allmodconfig, and that is eating the stack? Tomi