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 3AE68C433F5 for ; Fri, 7 Jan 2022 14:39:32 +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:MIME-Version:References:In-Reply-To: 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=kGIoInr1HKYXVKzt+0q6qE6Olo8E7pYGdfFf/fVmhk8=; b=DX1VAcysAc5yRT mH6abfP4zFXC5lbtwqKwitW1/kJuPPAI6Jj07aTjgkZ6bO4DbA212KuCltKlQ/JTWwxaDE59wMeHY fBQEEekCnbTW04tN0gobJ2aJ9Z1Jn0fh9uVip5Am8FuBdPN92PbE/jTjO8RlpckasiX9+MKUXkN7R nFXereE4SyCJAS87RefhYZ6rIV5bmkDzmjVcrvU8wB4QX1F/Z1r3jbHt5dnk64ojO35X3uLCodicA pO5PbmxdFAGDjsllU8sF1SHZB4teQYS6r6XGBl8tvtRSdfSY8V5sbbxVvWP+PJ7KkXnLpobd4e7nD NAMMr7KK3APk9v2Wh4SA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1n5qNn-004FHl-7A; Fri, 07 Jan 2022 14:38:19 +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 1n5qNj-004FGD-1h for linux-arm-kernel@lists.infradead.org; Fri, 07 Jan 2022 14:38:16 +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 4B28013A1; Fri, 7 Jan 2022 06:38:14 -0800 (PST) Received: from donnerap.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A106D3F774; Fri, 7 Jan 2022 06:38:13 -0800 (PST) Date: Fri, 7 Jan 2022 14:38:11 +0000 From: Andre Przywara To: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, Jaxson Han Subject: Re: [boot-wrapper PATCH v2 3/9] Makefile: Tell compiler to generate bare-metal code Message-ID: <20220107143811.3d193704@donnerap.cambridge.arm.com> In-Reply-To: References: <20211222181607.1203191-1-andre.przywara@arm.com> <20211222181607.1203191-4-andre.przywara@arm.com> Organization: ARM X-Mailer: Claws Mail 3.17.5 (GTK+ 2.24.32; aarch64-unknown-linux-gnu) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220107_063815_194622_666144AA X-CRM114-Status: GOOD ( 28.43 ) 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 On Fri, 7 Jan 2022 13:53:50 +0000 Mark Rutland wrote: Hi Mark, > On Wed, Dec 22, 2021 at 06:16:01PM +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 and headers, since they might pull in more code than > > we want, and might not run well in the boot-wrapper environment. > > > > This also enables optimisation, since it produces much better code and > > tends to avoid problems due to missing inlining, for instance. > > I'd appreciate if we could add some explanation for these (just in the commit > message is fine), as e.g. it's not clear to me why -fno-toplevel-reorder is > necessary. Yeah, I was expecting some discussion about this. I went over most options from the manpage a while ago (for some unrelated baremetal code project), and decided for each option whether it would make sense or not. TBH I don't remember every detail from that, but I can certainly just drop the less critical options from that list. And I would be happy to add some rationale for each of them, but wonder what the best place would be? I'd rather do this in a file than in a commit message, would you prefer comments in Makefile.am, or in README or a separate file, with a pointer from Makefile.am. Or in a commit message anyway? Cheers, Andre > > > > Signed-off-by: Andre Przywara > > --- > > Makefile.am | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/Makefile.am b/Makefile.am > > index 3e970a3..d9ad6d1 100644 > > --- a/Makefile.am > > +++ b/Makefile.am > > @@ -124,9 +124,14 @@ CHOSEN_NODE := chosen { \ > > > > CPPFLAGS += $(INITRD_FLAGS) > > CFLAGS += -I$(top_srcdir)/include/ -I$(top_srcdir)/$(ARCH_SRC)/include/ > > -CFLAGS += -Wall -fomit-frame-pointer > > +CFLAGS += -Wall -Wstrict-prototypes -fomit-frame-pointer > > +CFLAGS += -ffreestanding -nostdinc -nostdlib > > +CFLAGS += -fno-common -fno-strict-aliasing -fno-stack-protector > > +CFLAGS += -fno-toplevel-reorder > > +CFLAGS += -fno-unwind-tables -fno-asynchronous-unwind-tables > > CFLAGS += -ffunction-sections -fdata-sections > > CFLAGS += -fno-pic -fno-pie > > +CFLAGS += -Os > > LDFLAGS += --gc-sections > > > > OBJ := $(addprefix $(ARCH_SRC),$(ARCH_OBJ)) $(addprefix $(COMMON_SRC),$(COMMON_OBJ)) > > -- > > 2.25.1 > > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel