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=-15.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 D714AC433DB for ; Thu, 11 Feb 2021 09:04:47 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id DAFA864DE7 for ; Thu, 11 Feb 2021 09:04:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DAFA864DE7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=csgroup.eu Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4DbrL409kKzDwqM for ; Thu, 11 Feb 2021 20:04:44 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=csgroup.eu (client-ip=93.17.236.30; helo=pegase1.c-s.fr; envelope-from=christophe.leroy@csgroup.eu; receiver=) Received: from pegase1.c-s.fr (pegase1.c-s.fr [93.17.236.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4DbrJ26dRLzDwkp for ; Thu, 11 Feb 2021 20:02:52 +1100 (AEDT) Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4DbrHn6YFnz9v1r3; Thu, 11 Feb 2021 10:02:45 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id I3uV6Lov9Lcj; Thu, 11 Feb 2021 10:02:45 +0100 (CET) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4DbrHn5jcJz9v1qx; Thu, 11 Feb 2021 10:02:45 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id D48E48B81A; Thu, 11 Feb 2021 10:02:46 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id m6etzR6U-SJI; Thu, 11 Feb 2021 10:02:46 +0100 (CET) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 469BC8B81B; Thu, 11 Feb 2021 10:02:46 +0100 (CET) Subject: Re: [PATCH] powerpc/traps: Declare unrecoverable_exception() as __noreturn To: Gabriel Paubert References: <20210211074723.GA16987@lt-gp.iram.es> From: Christophe Leroy Message-ID: <51da512b-3d00-fb5e-7abc-60688960df65@csgroup.eu> Date: Thu, 11 Feb 2021 10:02:58 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210211074723.GA16987@lt-gp.iram.es> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-kernel@vger.kernel.org, npiggin@gmail.com, Paul Mackerras , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Le 11/02/2021 à 08:47, Gabriel Paubert a écrit : > On Thu, Feb 11, 2021 at 06:34:43AM +0000, Christophe Leroy wrote: >> unrecoverable_exception() is never expected to return, most callers >> have an infiniteloop in case it returns. >> >> Ensure it really never returns by terminating it with a BUG(), and >> declare it __no_return. >> >> It always GCC to really simplify functions calling it. In the exemple below, > > s/always/allows ? Yes > > (Otherwise I can't parse it.) > >> it avoids the stack frame in the likely fast path and avoids code duplication >> for the exit. > > Indeed, nice code generation improvement. > >> >> With this patch: >> >> 00000348 : >> 348: 81 43 00 84 lwz r10,132(r3) >> 34c: 71 48 00 02 andi. r8,r10,2 >> 350: 41 82 00 2c beq 37c >> 354: 71 4a 40 00 andi. r10,r10,16384 >> 358: 40 82 00 20 bne 378 >> 35c: 80 62 00 70 lwz r3,112(r2) >> 360: 74 63 00 01 andis. r3,r3,1 >> 364: 40 82 00 28 bne 38c >> 368: 7d 40 00 a6 mfmsr r10 >> 36c: 7c 11 13 a6 mtspr 81,r0 >> 370: 7c 12 13 a6 mtspr 82,r0 >> 374: 4e 80 00 20 blr >> 378: 48 00 00 00 b 378 > > Infinite loop (seems to be on test of MSR_PR)? Yes, that's what you get when CONFIG_BUG is not selected. /include/asm-generic/bug.h: #ifndef HAVE_ARCH_BUG #define BUG() do {} while (1) #endif > > Gabriel > >> 37c: 94 21 ff f0 stwu r1,-16(r1) >> 380: 7c 08 02 a6 mflr r0 >> 384: 90 01 00 14 stw r0,20(r1) >> 388: 48 00 00 01 bl 388 >> 388: R_PPC_REL24 unrecoverable_exception >> 38c: 38 e2 00 70 addi r7,r2,112 >> 390: 3d 00 00 01 lis r8,1 >> 394: 7c c0 38 28 lwarx r6,0,r7 >> 398: 7c c6 40 78 andc r6,r6,r8 >> 39c: 7c c0 39 2d stwcx. r6,0,r7 >> 3a0: 40 a2 ff f4 bne 394 >> 3a4: 38 60 00 01 li r3,1 >> 3a8: 4b ff ff c0 b 368 >> >> Without this patch: >> >> 00000348 : >> 348: 94 21 ff f0 stwu r1,-16(r1) >> 34c: 93 e1 00 0c stw r31,12(r1) >> 350: 7c 7f 1b 78 mr r31,r3 >> 354: 81 23 00 84 lwz r9,132(r3) >> 358: 71 2a 00 02 andi. r10,r9,2 >> 35c: 41 82 00 34 beq 390 >> 360: 71 29 40 00 andi. r9,r9,16384 >> 364: 40 82 00 28 bne 38c >> 368: 80 62 00 70 lwz r3,112(r2) >> 36c: 74 63 00 01 andis. r3,r3,1 >> 370: 40 82 00 3c bne 3ac >> 374: 7d 20 00 a6 mfmsr r9 >> 378: 7c 11 13 a6 mtspr 81,r0 >> 37c: 7c 12 13 a6 mtspr 82,r0 >> 380: 83 e1 00 0c lwz r31,12(r1) >> 384: 38 21 00 10 addi r1,r1,16 >> 388: 4e 80 00 20 blr >> 38c: 48 00 00 00 b 38c >> 390: 7c 08 02 a6 mflr r0 >> 394: 90 01 00 14 stw r0,20(r1) >> 398: 48 00 00 01 bl 398 >> 398: R_PPC_REL24 unrecoverable_exception >> 39c: 80 01 00 14 lwz r0,20(r1) >> 3a0: 81 3f 00 84 lwz r9,132(r31) >> 3a4: 7c 08 03 a6 mtlr r0 >> 3a8: 4b ff ff b8 b 360 >> 3ac: 39 02 00 70 addi r8,r2,112 >> 3b0: 3d 40 00 01 lis r10,1 >> 3b4: 7c e0 40 28 lwarx r7,0,r8 >> 3b8: 7c e7 50 78 andc r7,r7,r10 >> 3bc: 7c e0 41 2d stwcx. r7,0,r8 >> 3c0: 40 a2 ff f4 bne 3b4 >> 3c4: 38 60 00 01 li r3,1 >> 3c8: 4b ff ff ac b 374 >> >> Signed-off-by: Christophe Leroy >> --- >> arch/powerpc/include/asm/interrupt.h | 2 +- >> arch/powerpc/kernel/interrupt.c | 1 - >> arch/powerpc/kernel/traps.c | 2 ++ >> 3 files changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h >> index dcff30e3919b..fa8bfb91f8df 100644 >> --- a/arch/powerpc/include/asm/interrupt.h >> +++ b/arch/powerpc/include/asm/interrupt.h >> @@ -411,7 +411,7 @@ DECLARE_INTERRUPT_HANDLER(altivec_assist_exception); >> DECLARE_INTERRUPT_HANDLER(CacheLockingException); >> DECLARE_INTERRUPT_HANDLER(SPEFloatingPointException); >> DECLARE_INTERRUPT_HANDLER(SPEFloatingPointRoundException); >> -DECLARE_INTERRUPT_HANDLER(unrecoverable_exception); >> +DECLARE_INTERRUPT_HANDLER(unrecoverable_exception) __noreturn; >> DECLARE_INTERRUPT_HANDLER(WatchdogException); >> DECLARE_INTERRUPT_HANDLER(kernel_bad_stack); >> >> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c >> index eca3be36c18c..7e7106641ca9 100644 >> --- a/arch/powerpc/kernel/interrupt.c >> +++ b/arch/powerpc/kernel/interrupt.c >> @@ -440,7 +440,6 @@ notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned >> return ret; >> } >> >> -void unrecoverable_exception(struct pt_regs *regs); >> void preempt_schedule_irq(void); >> >> notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs, unsigned long msr) >> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c >> index 2afa05ad21c8..1ff776e9e8e3 100644 >> --- a/arch/powerpc/kernel/traps.c >> +++ b/arch/powerpc/kernel/traps.c >> @@ -2173,6 +2173,8 @@ DEFINE_INTERRUPT_HANDLER(unrecoverable_exception) >> pr_emerg("Unrecoverable exception %lx at %lx (msr=%lx)\n", >> regs->trap, regs->nip, regs->msr); >> die("Unrecoverable exception", regs, SIGABRT); >> + /* die() should not return */ >> + BUG(); >> } >> NOKPROBE_SYMBOL(unrecoverable_exception); >> >> -- >> 2.25.0 >> > >