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=-15.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 6BED1C433DB for ; Thu, 11 Feb 2021 07:49:32 +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 89DD364DE7 for ; Thu, 11 Feb 2021 07:49:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 89DD364DE7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=iram.es 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 4DbpgF323QzDwnN for ; Thu, 11 Feb 2021 18:49:29 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=iram.es (client-ip=130.206.19.145; helo=mx01.puc.rediris.es; envelope-from=paubert@iram.es; receiver=) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=iram.es header.i=@iram.es header.a=rsa-sha256 header.s=DKIM header.b=DZcgZrhH; dkim-atps=neutral Received: from mx01.puc.rediris.es (outbound4mad.lav.puc.rediris.es [130.206.19.145]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4DbpdT2DzCzDwlV for ; Thu, 11 Feb 2021 18:47:56 +1100 (AEDT) Received: from mta-out01.sim.rediris.es (mta-out01.sim.rediris.es [130.206.24.43]) by mx01.puc.rediris.es with ESMTP id 11B7lT6B003872-11B7lT6D003872 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Thu, 11 Feb 2021 08:47:33 +0100 Received: from mta-out01.sim.rediris.es (localhost.localdomain [127.0.0.1]) by mta-out01.sim.rediris.es (Postfix) with ESMTPS id 40A923254FBB; Thu, 11 Feb 2021 08:47:29 +0100 (CET) Received: from localhost (localhost.localdomain [127.0.0.1]) by mta-out01.sim.rediris.es (Postfix) with ESMTP id 31CDD3254FBA; Thu, 11 Feb 2021 08:47:29 +0100 (CET) X-Amavis-Modified: Mail body modified (using disclaimer) - mta-out01.sim.rediris.es Received: from mta-out01.sim.rediris.es ([127.0.0.1]) by localhost (mta-out01.sim.rediris.es [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id rXaFOftgOWwa; Thu, 11 Feb 2021 08:47:29 +0100 (CET) Received: from lt-gp.iram.es (75.red-88-27-245.staticip.rima-tde.net [88.27.245.75]) by mta-out01.sim.rediris.es (Postfix) with ESMTPA id 8A47C3036A81; Thu, 11 Feb 2021 08:47:28 +0100 (CET) Date: Thu, 11 Feb 2021 08:47:23 +0100 From: Gabriel Paubert To: Christophe Leroy Subject: Re: [PATCH] powerpc/traps: Declare unrecoverable_exception() as __noreturn Message-ID: <20210211074723.GA16987@lt-gp.iram.es> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-FE-Policy-ID: 2:8:0:SYSTEM DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; d=iram.es; s=DKIM; c=relaxed/relaxed; h=date:from:to:cc:subject:message-id:references:mime-version:content-type; bh=62bKwosBXY6XmYVjgzD+LnZH4mNcQ/c/3yeRBNQKXKA=; b=DZcgZrhHNpyppb7xOAZjzKLK7nMmaIMY2g8VWNKyY6t/u1Xgg2U3LIJlOy80NnWRXif97qsU1kR/ CrDwLnDAJ/sdg5gOpYffupYGYQLyMkUo9RnZgnitkDakPXqwMrdnp6YusSVRYNVHGoOqktRbLyZD 36m5FzzfCvgbZbv9Jdr9rldNCs9EUThfxGsdR0DUpiQYCokzC788T4q9oNLxkfQj51l4L1QFm0BW hge2m8Bp/TRlT618gNkqa63Mx9Sv+UbswTEdNqSG/m/Y76lSaQJegp5VMmDwp2QFNZQrVTOLKsOg FXdlMMp15lhE9Rsb8xtHE5kZxp6oEX2XvBCh/w== 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" 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 ? (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)? 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 >