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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 7F9C3C433DF for ; Wed, 27 May 2020 20:02:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 64E7720835 for ; Wed, 27 May 2020 20:02:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387459AbgE0UCj (ORCPT ); Wed, 27 May 2020 16:02:39 -0400 Received: from foss.arm.com ([217.140.110.172]:44210 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726114AbgE0UCj (ORCPT ); Wed, 27 May 2020 16:02:39 -0400 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 7394C31B; Wed, 27 May 2020 13:02:38 -0700 (PDT) Received: from [10.57.2.168] (unknown [10.57.2.168]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 45AE93F52E; Wed, 27 May 2020 13:02:36 -0700 (PDT) Subject: Re: [PATCH] arm64: vdso32: force vdso32 to be compiled as -marm From: Robin Murphy To: Nick Desaulniers Cc: Naohiro Aota , Stephen Boyd , Catalin Marinas , Masahiro Yamada , LKML , Manoj Gupta , Luis Lozano , Nathan Chancellor , Vincenzo Frascino , Will Deacon , Linux ARM References: <20200526173117.155339-1-ndesaulniers@google.com> <2f58c2a4-0f37-d507-7767-00161c6b5d98@arm.com> <34f261f7-c4b5-a628-9a4c-eb97b75fba52@arm.com> Message-ID: Date: Wed, 27 May 2020 21:02:33 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <34f261f7-c4b5-a628-9a4c-eb97b75fba52@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-05-27 20:28, Robin Murphy wrote: > On 2020-05-27 18:55, Nick Desaulniers wrote: >> On Wed, May 27, 2020 at 6:45 AM Robin Murphy >> wrote: >>> >>> On 2020-05-26 18:31, Nick Desaulniers wrote: >>>> Custom toolchains that modify the default target to -mthumb cannot >>>> compile the arm64 compat vdso32, as >>>> arch/arm64/include/asm/vdso/compat_gettimeofday.h >>>> contains assembly that's invalid in -mthumb.  Force the use of -marm, >>>> always. >>> >>> FWIW, this seems suspicious - the only assembly instructions I see there >>> are SWI(SVC), MRRC, and a MOV, all of which exist in Thumb for the >>> -march=armv7a baseline that we set. >>> >>> On a hunch, I've just bodged "VDSO_CFLAGS += -mthumb" into my tree and >>> built a Thumb VDSO quite happily with Ubuntu 19.04's >>> gcc-arm-linux-gnueabihf. What was the actual failure you saw? >> >>  From the link in the commit message: `write to reserved register 'R7'` >> https://godbolt.org/z/zwr7iZ >> IIUC r7 is reserved for the frame pointer in THUMB? > > It can be, if you choose to build with frame pointers and the common > frame pointer ABI for Thumb code that uses r7. However it can also be > for other things like the syscall number in the Arm syscall ABI too. I Oh, and for the avoidance of ambiguity that's "Arm" as in the 32-bit Arm architecture port, not a specific instruction set. Robin. > take it Clang has decided that writing syscall wrappers with minimal > inline asm is not a thing people deserve to do without arbitrary other > restrictions? > >> What is the implicit default of your gcc-arm-linux-gnueabihf at -O2? >> -mthumb, or -marm? > > As Dave pointed out, like the probable majority of users it's Thumb: > > $ arm-linux-gnueabihf-gcc -v > Using built-in specs. > COLLECT_GCC=arm-linux-gnueabihf-gcc > COLLECT_LTO_WRAPPER=/usr/lib/gcc-cross/arm-linux-gnueabihf/8/lto-wrapper > Target: arm-linux-gnueabihf > Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro > 8.3.0-6ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs > --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++ --prefix=/usr > --with-gcc-major-version-only --program-suffix=-8 --enable-shared > --enable-linker-build-id --libexecdir=/usr/lib > --without-included-gettext --enable-threads=posix --libdir=/usr/lib > --enable-nls --with-sysroot=/ --enable-clocale=gnu > --enable-libstdcxx-debug --enable-libstdcxx-time=yes > --with-default-libstdcxx-abi=new --enable-gnu-unique-object > --disable-libitm --disable-libquadmath --disable-libquadmath-support > --enable-plugin --enable-default-pie --with-system-zlib > --with-target-system-zlib --enable-multiarch --enable-multilib > --disable-sjlj-exceptions --with-arch=armv7-a --with-fpu=vfpv3-d16 > --with-float=hard --with-mode=thumb --disable-werror --enable-multilib > --enable-checking=release --build=aarch64-linux-gnu > --host=aarch64-linux-gnu --target=arm-linux-gnueabihf > --program-prefix=arm-linux-gnueabihf- > --includedir=/usr/arm-linux-gnueabihf/include > Thread model: posix > gcc version 8.3.0 (Ubuntu/Linaro 8.3.0-6ubuntu1) > > (yeah, I didn't actually need to hack my makefile at all) > > Robin. > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel