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=-9.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT 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 87868C43331 for ; Thu, 5 Sep 2019 17:15:16 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 1456420828 for ; Thu, 5 Sep 2019 17:15:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1456420828 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 628554A586; Thu, 5 Sep 2019 13:15:15 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id wis2kS1QSxDj; Thu, 5 Sep 2019 13:15:14 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 3089D4A4F6; Thu, 5 Sep 2019 13:15:14 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id EF2684A4F6 for ; Thu, 5 Sep 2019 13:15:12 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id bVBtpz+xIOC0 for ; Thu, 5 Sep 2019 13:15:11 -0400 (EDT) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 17F584A479 for ; Thu, 5 Sep 2019 13:15:11 -0400 (EDT) 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 80B43337; Thu, 5 Sep 2019 10:15:10 -0700 (PDT) Received: from donnerap.arm.com (donnerap.cambridge.arm.com [10.1.197.44]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 986843F718; Thu, 5 Sep 2019 10:15:09 -0700 (PDT) From: Andre Przywara To: Andrew Jones Subject: [PATCH kvm-unit-tests] arm: prevent compiler from using unaligned accesses Date: Thu, 5 Sep 2019 18:15:02 +0100 Message-Id: <20190905171502.215183-1-andre.przywara@arm.com> X-Mailer: git-send-email 2.17.1 Cc: Paolo Bonzini , kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu The ARM architecture requires all accesses to device memory to be naturally aligned[1][2]. Normal memory does not have this strict requirement, and in fact many systems do ignore unaligned accesses (by the means of clearing the A bit in SCTLR and accessing normal memory). So the default behaviour of GCC assumes that unaligned accesses are fine, at least if happening on the stack. Now kvm-unit-tests runs some C code with the MMU off, which degrades the whole system memory to device memory. Now every unaligned access will fault, regardless of the A bit. In fact there is at least one place in lib/printf.c where GCC merges two consecutive char* accesses into one "strh" instruction, writing to a potentially unaligned address. This can be reproduced by configuring kvm-unit-tests for kvmtool, but running it on QEMU, which triggers an early printf that exercises this particular code path. Add the -mstrict-align compiler option to the arm64 CFLAGS to fix this problem. Also add the respective -mno-unaligned-access flag for arm. Thanks to Alexandru for helping debugging this. Signed-off-by: Andre Przywara [1] ARMv8 ARM DDI 0487E.a, B2.5.2 [2] ARMv7 ARM DDI 0406C.d, A3.2.1 --- arm/Makefile.arm | 1 + arm/Makefile.arm64 | 1 + 2 files changed, 2 insertions(+) diff --git a/arm/Makefile.arm b/arm/Makefile.arm index a625267..43b4be1 100644 --- a/arm/Makefile.arm +++ b/arm/Makefile.arm @@ -12,6 +12,7 @@ KEEP_FRAME_POINTER := y CFLAGS += $(machine) CFLAGS += -mcpu=$(PROCESSOR) +CFLAGS += -mno-unaligned-access arch_LDFLAGS = -Ttext=40010000 diff --git a/arm/Makefile.arm64 b/arm/Makefile.arm64 index 02c24e8..35de5ea 100644 --- a/arm/Makefile.arm64 +++ b/arm/Makefile.arm64 @@ -7,6 +7,7 @@ bits = 64 ldarch = elf64-littleaarch64 arch_LDFLAGS = -pie -n +CFLAGS += -mstrict-align define arch_elf_check = $(if $(shell ! $(OBJDUMP) -R $(1) >&/dev/null && echo "nok"), -- 2.17.1 _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm