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 X-Spam-Level: X-Spam-Status: No, score=-19.6 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CA67FC49ED6 for ; Wed, 11 Sep 2019 21:02:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9559120838 for ; Wed, 11 Sep 2019 21:02:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="o7jCP9O6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730663AbfIKVCP (ORCPT ); Wed, 11 Sep 2019 17:02:15 -0400 Received: from mail-pf1-f193.google.com ([209.85.210.193]:43962 "EHLO mail-pf1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728877AbfIKVCP (ORCPT ); Wed, 11 Sep 2019 17:02:15 -0400 Received: by mail-pf1-f193.google.com with SMTP id d15so14451459pfo.10 for ; Wed, 11 Sep 2019 14:02:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=BmSGku8jGWaQdEnWgjS8EmzhMwO0vQvjKEtMVStz3ho=; b=o7jCP9O619jk1A8fcSgzAWayhUVzV5ZQt3XJGgqVC4Cr2Y27xwM0ppsCKWoztQnBFe tlxVQygRIqQmFJPuPR0h2TaKn4X28eymj7iEHy5QfNAzcyw+h1PHy6PhWu/NIY0vZMBD n8pKo9xFCJvpTQpvkgIwlpo9ZNi2ZaT4Bkcdn6IxwAkMN5z2jFsk2bu8EFNjZl6wMEPv YZC/7ZBuOj536hHif/679mreNnVxNJUZkYm1f6nUwWPEsPE5MNIzLc6w4DQkazrLePDv 5uZcD2N56xzSI7oEnq+PfQ5t/ZsBvVzrsSMF1zLSk6B4FwV1Anb0Q3Zq6mkj+Sm0LfyE 8ZLA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=BmSGku8jGWaQdEnWgjS8EmzhMwO0vQvjKEtMVStz3ho=; b=bPM1U3QdDe3MAIZfv9LqEm2z8WiUQeFED0OTo8Fcq7i6pUZ9YtAk0vWPhQbWHA7ph3 lBDnnCQOG0hvKJ4t6b9hXX4qiWQ+flVnfIwsbt5AdFVpeu4FFwKOhbuRvv915J4j076U OT+TSkC3gcYgZTazklBtiKTMYxwievMdhkPQ4lwcMucIiSuBXeXccVoLEh73qpycGP9p m4lbxb9Sg4zxfBHI0S0dB4n0+qSHZ8WuRw4xK1OuGc9/pGlBLWrQxgpRZFWExlopSq3J dueTEuKCxJaFDBPHqRGWoZUsCPUXiSUnXd4JHM9osVnBxokXSRpzqAGXXPtD49SuMDRu tp9A== X-Gm-Message-State: APjAAAUB+m3df2jO5TVHRHp6qKA8J0Pyyqt7jAnBKYexqKzFJrSGDA3c ugaKtliDO3W257IFvexaZ9fG7RP1KR35V5LydcCIVg== X-Google-Smtp-Source: APXvYqypx9sTdaUqWPw1cVmR3te2mC9wx57XFuE4p0MZXxepRD5h/5pwdXHJeHB20U1iiWL6kUo2AHVEcIsr6mTHga0= X-Received: by 2002:a65:690b:: with SMTP id s11mr34339694pgq.10.1568235730928; Wed, 11 Sep 2019 14:02:10 -0700 (PDT) MIME-Version: 1.0 References: <20190911182049.77853-1-natechancellor@gmail.com> <20190911182049.77853-4-natechancellor@gmail.com> In-Reply-To: <20190911182049.77853-4-natechancellor@gmail.com> From: Nick Desaulniers Date: Wed, 11 Sep 2019 14:01:59 -0700 Message-ID: Subject: Re: [PATCH v3 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp To: Nathan Chancellor Cc: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , linuxppc-dev , LKML , clang-built-linux Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 11, 2019 at 11:21 AM Nathan Chancellor wrote: > > r370454 gives LLVM the ability to convert certain loops into a reference > to bcmp as an optimization; this breaks prom_init_check.sh: > > CALL arch/powerpc/kernel/prom_init_check.sh > Error: External symbol 'bcmp' referenced from prom_init.c > make[2]: *** [arch/powerpc/kernel/Makefile:196: prom_init_check] Error 1 > > bcmp is defined in lib/string.c as a wrapper for memcmp so this could be > added to the whitelist. However, commit 450e7dd4001f ("powerpc/prom_init: > don't use string functions from lib/") copied memcmp as prom_memcmp to > avoid KASAN instrumentation so having bcmp be resolved to regular memcmp > would break that assumption. Furthermore, because the compiler is the > one that inserted bcmp, we cannot provide something like prom_bcmp. > > To prevent LLVM from being clever with optimizations like this, use > -ffreestanding to tell LLVM we are not hosted so it is not free to make > transformations like this. > > Link: https://github.com/ClangBuiltLinux/linux/issues/647 > Link: https://github.com/llvm/llvm-project/commit/5c9f3cfec78f9e9ae013de9a0d092a68e3e79e002 The above link doesn't work for me (HTTP 404). PEBKAC? https://github.com/llvm/llvm-project/commit/5c9f3cfec78f9e9ae013de9a0d092a68e3e79e002 > Signed-off-by: Nathan Chancellor > --- > > New patch in the series so no previous version. > > arch/powerpc/kernel/Makefile | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile > index 19f19c8c874b..aa78b3f6271e 100644 > --- a/arch/powerpc/kernel/Makefile > +++ b/arch/powerpc/kernel/Makefile > @@ -21,7 +21,7 @@ CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) > CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) > CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) > > -CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector) > +CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector) -ffreestanding > > ifdef CONFIG_FUNCTION_TRACER > # Do not trace early boot code > -- > 2.23.0 > -- Thanks, ~Nick Desaulniers