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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 818CEC433EF for ; Mon, 17 Jan 2022 16:48:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=OholM07U0Yc9MmaOyWmYLK3XZvdeS58rD/NPOBkHp20=; b=ZGtFWQD0mc8CrG k/qicUh82WZWbml7nvtr6CQ9HyeNE1T8vza0w4zHrgQ0ZKUmI+s4GTIq3yyTNuINpNgomd3XJdKAC LHQQs0puWR40FH1HIZKZ45TrSS5+Et7WhG0iU/89etYp8rczI0o0VXQzmxP8nZwTi6UdO2XtDOvJf rq2VZCpQiAPsVw4SyvyEy4R1dbsnoUY5TS6w+ao/aXEOBfCykAVm/rxj4HEkb3s8gi8i+PrXnmdoc iNg9WLHyRbJbN1sVEgpeyM8s0lEe7RN6ZvA4zI/SnpKGTMHaXZkuc1/ya7L0+zBOEp7Ewl6X4Mu3d EprxtJH1K/Mm6btL0CMQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1n9VAJ-00FcXq-ME; Mon, 17 Jan 2022 16:47:31 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1n9VAG-00FcXX-7E for linux-arm-kernel@lists.infradead.org; Mon, 17 Jan 2022 16:47:29 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0EE7911D4; Mon, 17 Jan 2022 08:47:27 -0800 (PST) Received: from C02TD0UTHF1T.local (unknown [10.57.38.30]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5407C3F766; Mon, 17 Jan 2022 08:47:26 -0800 (PST) Date: Mon, 17 Jan 2022 16:47:20 +0000 From: Mark Rutland To: Andre Przywara Cc: Jaxson Han , linux-arm-kernel@lists.infradead.org, Robin Murphy Subject: Re: [PATCH v3] Makefile: Tell compiler to generate bare-metal code Message-ID: <20220117164720.GA94025@C02TD0UTHF1T.local> References: <20220117153348.2513798-1-andre.przywara@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220117153348.2513798-1-andre.przywara@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220117_084728_353914_1E1890D0 X-CRM114-Status: GOOD ( 25.92 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Andre, On Mon, Jan 17, 2022 at 03:33:48PM +0000, Andre Przywara wrote: > Our GCC invocation does not provide many parameters, which lets the > toolchain fill in its own default setup. > In case of a native build or when using a full-featured cross-compiler, > this probably means Linux userland, which is not what we want for a > bare-metal application like boot-wrapper. > > Tell the compiler to forget about those standard settings, and only use > what we explicitly ask for. In particular that means to not use toolchain > provided libraries, since they might pull in more code than we want, and > might not run well in the boot-wrapper environment. Thanks for splitting this out; I'd like to apply this with two minor fixups (which I'll apply locally if you agree). > Disable the stack protector, as this adds code that relies on userland: > "If a guard check fails, an error message is printed and the program > exits." (from the gcc manpage). I think we should say: | Disable the stack protector, as this relies on support code, e.g. | a __stack_chk_guard variable and __stack_chk_fail function, which the | boot-wrapper does not implement. > Signed-off-by: Andre Przywara > --- > Hi, > > compared to [PATCH v2 3/9] this drops the more contentious options (for > now, at least), and focuses on what's really needed. Including > -fno-stack-protector, as the need for this showed up in the cleanup series > already. > > Cheers, > Andre > > Makefile.am | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/Makefile.am b/Makefile.am > index f941b07..581840e 100644 > --- a/Makefile.am > +++ b/Makefile.am > @@ -125,6 +125,8 @@ CHOSEN_NODE := chosen { \ > CPPFLAGS += $(INITRD_FLAGS) > CFLAGS += -I$(top_srcdir)/include/ -I$(top_srcdir)/$(ARCH_SRC)/include/ > CFLAGS += -Wall -fomit-frame-pointer > +CFLAGS += -ffreestanding -nostdlib # this is not for userland > +CFLAGS += -fno-stack-protector # no terminal to print For now, I'd like to drop these comments, since I think the "no terminal to print" comment is a bit confusing, and the "this is not for userland" comment is arguably the most obvious. Then as a future follow-up we can reoganise this for clarity: | # Build code suitable for a bare-metal environment which does not | # depend on any support libraries | CFLAGS += ffreestanding -nostdlib | | # Disable unnecessary features which require runtime support | CFLAGS += -fno-stack-protector | CFLAGS += ... | | # Disable unnecessary features which impact code-size | CFLAGS += -fomit-frame-pointer | CFLAGS += ... | | # Allow the linker to remove unused code and data to shrink the | # resulting binary | CFLAGS += -ffunction-sections -fdata-sections | LDFLAGS += --gc-sections > CFLAGS += -ffunction-sections -fdata-sections > CFLAGS += -fno-pic -fno-pie > LDFLAGS += --gc-sections > -- > 2.25.1 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel