From patchwork Wed Jul 19 19:00:25 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Arnd Bergmann X-Patchwork-Id: 13319385 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 542F5C0015E for ; Wed, 19 Jul 2023 19:00:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229553AbjGSTAy (ORCPT ); Wed, 19 Jul 2023 15:00:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41892 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229492AbjGSTAy (ORCPT ); Wed, 19 Jul 2023 15:00:54 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0E2D5171E; Wed, 19 Jul 2023 12:00:53 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 94C0A617D8; Wed, 19 Jul 2023 19:00:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C4308C433C7; Wed, 19 Jul 2023 19:00:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1689793252; bh=m8elIMgvNx0HITJE8wfTnOPbpAfIc6OxVFEIrgi6Ew8=; h=From:To:Cc:Subject:Date:From; b=DjlKZMgfXAhCiIO7wXFE/nLLfkycJD34db9ewHFpZ9oT9ADKGwF1dnYTDthUFvL9q L4duYNtIxCemXki5jslS2vAAhMOgdhrFlpZrxBvGx8eqQod0lhKKmtWFzlbUtUCDpC etDaMPL+oXFbmsEGkdJ8KgRACK9zXToeo3M0FA0UHF1RjXLaKupxXcPgNttkdiCPEL mtdYGpBxr/gtUp+sG9k2rfwLvIpJSRaGT4UheoGgE7mlA6FiHHTctW6MUly2M3+V8x DAI4aUx1iOKYyvCeIfFigHmEPXItG9RYLkP8PKJ57cOEdyEtLrxkSQiU1eMn/hp3hw nFXkNu+H55+eA== From: Arnd Bergmann To: Tudor Ambarus , Pratyush Yadav , Miquel Raynal , Richard Weinberger , Vignesh Raghavendra Cc: Arnd Bergmann , Peter Foley , Pedro Falcato , Michael Walle , Mark Brown , Takahiro Kuwano , Dhruva Gole , linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org, linux-spi@vger.kernel.org Subject: [PATCH] mtd: spi-nor: avoid holes in struct spi_mem_op Date: Wed, 19 Jul 2023 21:00:25 +0200 Message-Id: <20230719190045.4007391-1-arnd@kernel.org> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-spi@vger.kernel.org From: Arnd Bergmann gcc gets confused when -ftrivial-auto-var-init=pattern is used on sparse bit fields such as 'struct spi_mem_op', which caused the previous false positive warning about an uninitialized variable: drivers/mtd/spi-nor/spansion.c: error: 'op' is used uninitialized [-Werror=uninitialized] In fact, the variable is fully initialized and gcc does not see it being used, so the warning is entirely bogus. The problem appears to be a misoptimization in the initialization of single bit fields when the rest of the bytes are not initialized. A previous workaround added another initialization, which ended up shutting up the warning in spansion.c, though it apparently still happens in other files as reported by Peter Foley in the gcc bugzilla. The workaround of adding a fake initialization seems particularly bad because it would set values that can never be correct but prevent the compiler from warning about actually missing initializations. Revert the broken workaround and instead pad the structure to only have bitfields that add up to full bytes, which should avoid this behavior in all drivers. I also filed a new bug against gcc with what I found, so this can hopefully be addressed in future gcc releases. At the moment, only gcc-12 and gcc-13 are affected. Cc: Peter Foley Cc: Pedro Falcato Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110743 Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108402 Link: https://godbolt.org/z/efMMsG1Kx Fixes: 420c4495b5e56 ("mtd: spi-nor: spansion: make sure local struct does not contain garbage") Signed-off-by: Arnd Bergmann Acked-by: Mark Brown Acked-by: Tudor Ambarus --- drivers/mtd/spi-nor/spansion.c | 4 ++-- include/linux/spi/spi-mem.h | 4 ++++ 2 files changed, 6 insertions(+), 2 deletions(-) diff --git a/drivers/mtd/spi-nor/spansion.c b/drivers/mtd/spi-nor/spansion.c index 6d6466a3436e6..8397cf3cc3306 100644 --- a/drivers/mtd/spi-nor/spansion.c +++ b/drivers/mtd/spi-nor/spansion.c @@ -361,7 +361,7 @@ static int cypress_nor_determine_addr_mode_by_sr1(struct spi_nor *nor, */ static int cypress_nor_set_addr_mode_nbytes(struct spi_nor *nor) { - struct spi_mem_op op = {}; + struct spi_mem_op op; u8 addr_mode; int ret; @@ -492,7 +492,7 @@ s25fs256t_post_bfpt_fixup(struct spi_nor *nor, const struct sfdp_parameter_header *bfpt_header, const struct sfdp_bfpt *bfpt) { - struct spi_mem_op op = {}; + struct spi_mem_op op; int ret; ret = cypress_nor_set_addr_mode_nbytes(nor); diff --git a/include/linux/spi/spi-mem.h b/include/linux/spi/spi-mem.h index 8e984d75f5b6c..6b0a7dc48a4b7 100644 --- a/include/linux/spi/spi-mem.h +++ b/include/linux/spi/spi-mem.h @@ -101,6 +101,7 @@ struct spi_mem_op { u8 nbytes; u8 buswidth; u8 dtr : 1; + u8 __pad : 7; u16 opcode; } cmd; @@ -108,6 +109,7 @@ struct spi_mem_op { u8 nbytes; u8 buswidth; u8 dtr : 1; + u8 __pad : 7; u64 val; } addr; @@ -115,12 +117,14 @@ struct spi_mem_op { u8 nbytes; u8 buswidth; u8 dtr : 1; + u8 __pad : 7; } dummy; struct { u8 buswidth; u8 dtr : 1; u8 ecc : 1; + u8 __pad : 6; enum spi_mem_data_dir dir; unsigned int nbytes; union {