From patchwork Wed Oct 19 16:26:48 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Jason A. Donenfeld" X-Patchwork-Id: 13012162 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 43D12C43217 for ; Wed, 19 Oct 2022 16:27:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230259AbiJSQ1d (ORCPT ); Wed, 19 Oct 2022 12:27:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48470 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230180AbiJSQ1c (ORCPT ); Wed, 19 Oct 2022 12:27:32 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C945E43627; Wed, 19 Oct 2022 09:27:31 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 82681B8250F; Wed, 19 Oct 2022 16:27:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3CFB4C433D7; Wed, 19 Oct 2022 16:27:28 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="US7FiyUD" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1666196844; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=0lT+uEqlVaVxzDYYTi6dahuFCqqiYtCEv6lPMBO9aIk=; b=US7FiyUDe8pnYz6rD3uwg9fXnSMZscFIYdtfIpv4nXWoaXgeagZoP4Aq3+1ycyM4jN6PAA sT+vCEuPGTqjOb5tSTOdYoqhRAvMz/77p4eWWarEYDA2lmcA6GsdYvOM4SHdT534zEmMVR WZGPFOwIokjYZRMKO5MEMdMo3HOL2z4= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id f51d3b10 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Wed, 19 Oct 2022 16:27:24 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-arch@vger.kernel.org, linux-toolchains@vger.kernel.org Cc: "Jason A. Donenfeld" , Masahiro Yamada , Kees Cook , Andrew Morton , Linus Torvalds , Andy Shevchenko , Greg Kroah-Hartman Subject: [PATCH] kbuild: treat char as always signed Date: Wed, 19 Oct 2022 10:26:48 -0600 Message-Id: <20221019162648.3557490-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org Recently, some compile-time checking I added to the clamp_t family of functions triggered a build error when a poorly written driver was compiled on ARM, because the driver assumed that the naked `char` type is signed, but ARM treats it as unsigned, and the C standard says it's architecture-dependent. I doubt this particular driver is the only instance in which unsuspecting authors assume that `char` with no `signed` or `unsigned` designation is signed, because that's how the other types work. We were lucky enough this time that that driver used `clamp_t(char, negative_value, positive_value)`, so the new checking code found it, and I've sent a patch to fix it, but there are likely other places lurking that won't be so easily unearthed. So let's just eliminate this particular variety of heisensigned bugs entirely. Set `-fsigned-char` globally, so that gcc makes the type signed on all architectures. Cc: Masahiro Yamada Cc: Kees Cook Cc: Andrew Morton Cc: Linus Torvalds Cc: Andy Shevchenko Cc: Greg Kroah-Hartman Link: https://lore.kernel.org/lkml/202210190108.ESC3pc3D-lkp@intel.com/ Signed-off-by: Jason A. Donenfeld --- Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/Makefile b/Makefile index f41ec8c8426b..f1abcaf7110e 100644 --- a/Makefile +++ b/Makefile @@ -562,7 +562,7 @@ KBUILD_AFLAGS := -D__ASSEMBLY__ -fno-PIE KBUILD_CFLAGS := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs \ -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE \ -Werror=implicit-function-declaration -Werror=implicit-int \ - -Werror=return-type -Wno-format-security \ + -Werror=return-type -Wno-format-security -fsigned-char \ -std=gnu11 KBUILD_CPPFLAGS := -D__KERNEL__ KBUILD_RUSTFLAGS := $(rust_common_flags) \