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Tue, 30 Jun 2020 20:53:40 +0200 (CEST) Subject: Re: [PATCH v2] powerpc/uaccess: Use flexible addressing with __put_user()/__get_user() To: Segher Boessenkool Cc: Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , npiggin@gmail.com, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org References: <7b916759-1683-b4df-0d4b-b04b3fcd9a02@csgroup.eu> <878sg6862r.fsf@mpe.ellerman.id.au> <875zb98i5a.fsf@mpe.ellerman.id.au> <311c3471-cad7-72d5-a5e6-04cf892c5e41@csgroup.eu> <20200630163324.GW3598@gate.crashing.org> From: Christophe Leroy Message-ID: Date: Tue, 30 Jun 2020 18:53:39 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20200630163324.GW3598@gate.crashing.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/30/2020 04:33 PM, Segher Boessenkool wrote: > On Tue, Jun 30, 2020 at 04:55:05PM +0200, Christophe Leroy wrote: >> Le 30/06/2020 à 03:19, Michael Ellerman a écrit : >>> Michael Ellerman writes: >>>> Because it uses the "m<>" constraint which didn't work on GCC 4.6. >>>> >>>> https://github.com/linuxppc/issues/issues/297 >>>> >>>> So we should be able to pick it up for v5.9 hopefully. >>> >>> It seems to break the build with the kernel.org 4.9.4 compiler and >>> corenet64_smp_defconfig: >> >> Looks like 4.9.4 doesn't accept "m<>" constraint either. > > The evidence contradicts this assertion. > >> Changing it to "m" make it build. > > But that just means something else is wrong. > >>> + make -s CC=powerpc64-linux-gnu-gcc -j 160 >>> In file included from /linux/include/linux/uaccess.h:11:0, >>> from /linux/include/linux/sched/task.h:11, >>> from /linux/include/linux/sched/signal.h:9, >>> from /linux/include/linux/rcuwait.h:6, >>> from /linux/include/linux/percpu-rwsem.h:7, >>> from /linux/include/linux/fs.h:33, >>> from /linux/include/linux/huge_mm.h:8, >>> from /linux/include/linux/mm.h:675, >>> from /linux/arch/powerpc/kernel/signal_32.c:17: >>> /linux/arch/powerpc/kernel/signal_32.c: In function >>> 'save_user_regs.isra.14.constprop': >>> /linux/arch/powerpc/include/asm/uaccess.h:161:2: error: 'asm' operand has >>> impossible constraints >>> __asm__ __volatile__( \ >>> ^ >>> /linux/arch/powerpc/include/asm/uaccess.h:197:12: note: in expansion of >>> macro '__put_user_asm' >>> case 4: __put_user_asm(x, ptr, retval, "stw"); break; \ >>> ^ >>> /linux/arch/powerpc/include/asm/uaccess.h:206:2: note: in expansion of >>> macro '__put_user_size_allowed' >>> __put_user_size_allowed(x, ptr, size, retval); \ >>> ^ >>> /linux/arch/powerpc/include/asm/uaccess.h:220:2: note: in expansion of >>> macro '__put_user_size' >>> __put_user_size(__pu_val, __pu_addr, __pu_size, __pu_err); \ >>> ^ >>> /linux/arch/powerpc/include/asm/uaccess.h:96:2: note: in expansion of >>> macro '__put_user_nocheck' >>> __put_user_nocheck((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr))) >>> ^ >>> /linux/arch/powerpc/kernel/signal_32.c:120:7: note: in expansion of macro >>> '__put_user' >>> if (__put_user((unsigned int)gregs[i], &frame->mc_gregs[i])) >>> ^ > > Can we see what that was after the macro jungle? Like, the actual > preprocessed code? > Sorry for previous misunderstanding Here is the code: #define __put_user_asm(x, addr, err, op) \ __asm__ __volatile__( \ "1: " op "%U2%X2 %1,%2 # put_user\n" \ "2:\n" \ ".section .fixup,\"ax\"\n" \ "3: li %0,%3\n" \ " b 2b\n" \ ".previous\n" \ EX_TABLE(1b, 3b) \ : "=r" (err) \ : "r" (x), "m<>" (*addr), "i" (-EFAULT), "0" (err)) Christophe