From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 39A00106ACC9 for ; Thu, 12 Mar 2026 16:15:37 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9AEC110E082; Thu, 12 Mar 2026 16:15:36 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; secure) header.d=wbinvd.org header.i=@wbinvd.org header.b="eQ+2Oj82"; dkim-atps=neutral Received: from mail-dl1-f52.google.com (mail-dl1-f52.google.com [74.125.82.52]) by gabe.freedesktop.org (Postfix) with ESMTPS id 50C5210E082 for ; Thu, 12 Mar 2026 16:15:35 +0000 (UTC) Received: by mail-dl1-f52.google.com with SMTP id a92af1059eb24-128d2e3082eso453836c88.0 for ; Thu, 12 Mar 2026 09:15:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=wbinvd.org; s=wbinvd; t=1773332134; x=1773936934; darn=lists.freedesktop.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=wYTHfLNKxvy35JvH8B5/QuRK+srFMTLyCSw6VerOpmQ=; b=eQ+2Oj82pvx5Ky7KNDUV8ZEzz3wcITT3WyY8oogT73E63LbXrPtibaRdz+4MYdAYhT V2RO5gAvCnDPRQHft+P6DFCRDIOddfPUYDcT8eDaGEpl9+76tdsYwx0iUZmoqnCBqW57 d+3HtPrK4TVTvoJgER2te0TxnT0iSutYXagJ5fYMSQsmCMrvqyEEdz/dJBRU/3Vk3ZRI Xbh9osMVeSBmkPSv4YXSP/b3EM92XN/yWJUhlgIiVd10ckAIMe4s4S/iKpjFdsy6yeML xfSYo9oNBETpuwNJCvd+XXpXBfVEZKdEcsboGEJY1WLDjQ/6/j9OrL0u6DTzesM22gYF UpSw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1773332134; x=1773936934; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=wYTHfLNKxvy35JvH8B5/QuRK+srFMTLyCSw6VerOpmQ=; b=hWDORg+ffQX7oX5C2aybzfYc84EnbUFkY6e0oq+61VlB8Xbo0kXKj/oPDgoq8mUOeq WWgc75EBvZ1StA10phVLgR3CwXFoqMk2zopdforDnNFYS8G3REpBNJ1LnksCFlUTYLif Y4ZwYtg1ttKsvYsQslEMJ2p/Se1Teultu21JnpfAcO5Z3okw1DIj9dvGG2P2HctVzxt0 1ZwxKpU6t2kURYBahLTw4Lt2bZHu2ojuT2GPQIrdqPtz7mVKkGiTBo/6dtPvwbJKEG+u gRyHB3RNISGGrxdWvxVHxxr5AlpEB9bv76Ag0UkDUMzwTGH7GuDjLLFI72ceJfhtxXAr KlyQ== X-Forwarded-Encrypted: i=1; AJvYcCVguC79jW+yLHHSNLRITGI456PI5SkjUVTxgNXb2iZaQA6SzDYlHQsyNJyKPeWWnJ2q1oQutITSSys=@lists.freedesktop.org X-Gm-Message-State: AOJu0Ywztnp3lfrQyVzbilZVuolQSx1HZfm7hJHaujx3+phfPYlDluRB 7t6dpf2rT8ZMYYVJaOv5F3RsNw9rWFtCgi/LX++Td2RVQLrrT9T1jnW2MeM4w8uSWDM= X-Gm-Gg: ATEYQzwBxbBXU+fFOmX8FLoBm8jJg1z4IB6j4/2wcwmvH4xv3Y7HS0QHYzo0WDjuPfG YXRQAGhoD5fi23GazbgPNzRMEQaaSemsdLRzpD+BLu81QWckZHwP4XmSeyI2mWvajxJxNXJ18Q6 JFhJZNp9sS1U90shinn93R7csQAMkyBiYc39pjzddiM4eOIKhkMVcxUEIFLtwRCOJ3UVy2/4ItE 9IeVkUunI/JAw57CBB8E7Mo/WKzY785A/Gqsc6VOswdwJqqYL86HVt9JS+bMvo72p98g5vR24yy xlsjuKG+uYPfckyoxX5MPkfKEXqwJ+hCCyjbCzYfHyaVJIUi691UMQmTWHyBIPFXG29IFjS3UKq 34ni2WKZ3aviV/znnCnLKFJv6lghVjkh5g5PeeozE+Scqf0AxKuDiHw4v/xUOv6d1QabA15QpAj +OWyWSUw09UJKdfwxVqUcfRzH1Rw== X-Received: by 2002:a05:7300:ec17:b0:2ba:7783:d1cd with SMTP id 5a478bee46e88-2bea5475343mr137153eec.12.1773332134317; Thu, 12 Mar 2026 09:15:34 -0700 (PDT) Received: from mozart.vkv.me ([2001:5a8:468b:d015:53d0:dd05:1bb3:9034]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2be8aa7413esm6963232eec.24.2026.03.12.09.15.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Mar 2026 09:15:33 -0700 (PDT) Date: Thu, 12 Mar 2026 09:15:30 -0700 From: Calvin Owens To: Nathan Chancellor Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, Charlene Liu , Ovidiu Bunea , Alex Hung , Dan Wheeler , Alex Deucher , Harry Wentland , Leo Li , Rodrigo Siqueira , Christian Koenig , David Airlie , Simona Vetter , llvm@lists.linux.dev Subject: Re: [REGRESSION][PATCH] drm/amd/display: Fix uninitialized variable which breaks full LTO Message-ID: References: <20260312080245.GA3988095@ax162> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260312080245.GA3988095@ax162> X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Thursday 03/12 at 01:02 -0700, Nathan Chancellor wrote: > Hi Calvin, > > On Mon, Mar 09, 2026 at 09:24:57PM -0700, Calvin Owens wrote: > > Commit e1b385726f7f ("drm/amd/display: Add additional checks for PSP > > footer size") introduced a use of an uninitialized stack variable > > in dm_dmub_sw_init() (region_params.bss_data_size). > > > > Interestingly, this seems to cause no issue on normal kernels. But when > > full LTO is enabled, it causes the compiler to "optimize" out huge > > swaths of amdgpu initialization code, and the driver is unusable: > > Yeah, this appears to be a very unfortunate case of "clang encountered known > undefined behavior and stopped code generation", which we would like to > avoid but figuring out a proper upstreamable solution is hard. The most > recent attempt: > > https://github.com/llvm/llvm-project/pull/146791 > > My guess is that LTO allows inlining of > dmub_srv_get_fw_meta_info_from_raw_fw() into dm_dmub_sw_init(), at which > point it can see that the result of accessing an uninitialized > region_params.bss_data_size will be used through > fw_meta_info_params.fw_bss_data and gives up generating the rest of the > function. Thanks for looking Nathan. I'll keep an eye on that and see if it's able to catch this example. I've tried to come up with a minimal reproducer, but I haven't had any luck yet (so far I always get the warning), would that be helpful at all? I put the full W=2 output for the one file here in case anyone else wants to look: https://github.com/jcalvinowens/lkml-debug/blob/main/amdgpu-lto/gcc-warns.txt https://github.com/jcalvinowens/lkml-debug/blob/main/amdgpu-lto/llvm-warns.txt Somehow 'make drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.o' doesn't work, I want to look at that later because it was mildly annoying while digging into this. > > amdgpu 0000:03:00.0: [drm] Loading DMUB firmware via PSP: version=0x07002F00 > > amdgpu 0000:03:00.0: sw_init of IP block failed 5 > > amdgpu 0000:03:00.0: amdgpu_device_ip_init failed > > amdgpu 0000:03:00.0: Fatal error during GPU init > > > > It surprises me that neither gcc nor clang emit a warning about this: I > > only found it by bisecting the LTO breakage. > > gcc's -Wmaybe-uninitialized is disabled by default for the kernel but > even enabling it with KCFLAGS does not show an instance here, which I > find quite surprising... for clang, it is harder because the warning > happens early in the frontend where it might not be able to track a > value that well. GCC does flag what seems to me to be a real but benign warning about an ERR_PTR check that doesn't handle NULL in the same file: https://lore.kernel.org/lkml/6aaf2cf4bd19363a85f35e649685d7bdae400253.1773157137.git.calvin@wbinvd.org/ I'm also trying to find a minimal reproducer for GCC, no luck yet. > > Fix by using the old value for region_params.bss_data_size in place of > > the uninitialized reference, which makes amdgpu work with LTO again. > > > > Fixes: e1b385726f7f ("drm/amd/display: Add additional checks for PSP footer size") > > Signed-off-by: Calvin Owens > > --- > > drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c > > index b3d6f2cd8ab6..e69e61163ae9 100644 > > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c > > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c > > @@ -2554,7 +2554,7 @@ static int dm_dmub_sw_init(struct amdgpu_device *adev) > > fw_meta_info_params.fw_inst_const = adev->dm.dmub_fw->data + > > le32_to_cpu(hdr->header.ucode_array_offset_bytes) + > > PSP_HEADER_BYTES_256; > > - fw_meta_info_params.fw_bss_data = region_params.bss_data_size ? adev->dm.dmub_fw->data + > > + fw_meta_info_params.fw_bss_data = le32_to_cpu(hdr->bss_data_bytes) ? adev->dm.dmub_fw->data + > > Maybe it would be better to use fw_meta_info_params.bss_data_size > instead of le32_to_cpu(hdr->bss_data_bytes)? Obviously it is the same > value but it would result in a smaller change. It seems likely that this > was just a copy and paste failure. Agreed. That ends up being almost self evidently correct if I force git to add an extra context line with the assignment, I always forget I can do that: diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c index b3d6f2cd8ab6..0d1c772ef713 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -2553,9 +2553,9 @@ static int dm_dmub_sw_init(struct amdgpu_device *adev) fw_meta_info_params.bss_data_size = le32_to_cpu(hdr->bss_data_bytes); fw_meta_info_params.fw_inst_const = adev->dm.dmub_fw->data + le32_to_cpu(hdr->header.ucode_array_offset_bytes) + PSP_HEADER_BYTES_256; - fw_meta_info_params.fw_bss_data = region_params.bss_data_size ? adev->dm.dmub_fw->data + + fw_meta_info_params.fw_bss_data = fw_meta_info_params.bss_data_size ? adev->dm.dmub_fw->data + le32_to_cpu(hdr->header.ucode_array_offset_bytes) + le32_to_cpu(hdr->inst_const_bytes) : NULL; fw_meta_info_params.custom_psp_footer_size = 0; I'll send a v2 in a little bit. Thanks, Calvin > > le32_to_cpu(hdr->header.ucode_array_offset_bytes) + > > le32_to_cpu(hdr->inst_const_bytes) : NULL; > > fw_meta_info_params.custom_psp_footer_size = 0; > > -- > > 2.47.3 > >