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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 46D88C433EF for ; Thu, 3 Feb 2022 08:24:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=gpok0YWTVQ680KpssNShM87FZXf0g+LFQwSsTNQZl7U=; b=jvsgqO7EUEMmDq 8MJB4erEY2hnBPqZqHRp7CjbhEBFPeMM0lFq8Y2lqYmuwYhwC/0zSzVARBTvqhlEzUFgoCj1KTMRv MjpeZ/1Ckva0VcOUM9v7BdP1wPA+0SvflrrT58LITOqUgOdDKjwNmr0Q/lxFwXK+jqTS7If6jG3pW hM4MD//HycVZSho1BUpu+1Yd5M1EJh/wUxTIAEWHwzYPhuTtWWGPiu6swo03PW4uhKg/e76Mz2rRl lMHkD6hMGX4WDNpC5plGmxQNJhyuEFitW1ZwncHpEYF5uTTXf1Rt4iguWp/MerPpxHjV5RoBAiPzm e7YFIHdXyIEfLmnRWaew==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nFXOg-000JZA-DL; Thu, 03 Feb 2022 08:23:18 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nFXNq-000JHi-6K for linux-arm-kernel@lists.infradead.org; Thu, 03 Feb 2022 08:22:28 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 2DF4261843; Thu, 3 Feb 2022 08:22:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5133EC340F1; Thu, 3 Feb 2022 08:22:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1643876544; bh=FZEbuSgHaYWYJR7CBLSwWxcwsIaxd58F48DouMJwycU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Mhxmv2kGdvkX2lno571C6gh89K93L/W+J3o9JBuVGf0rZUTbbpma2uW8PnPCX/JkW GG2/eIYwhe9ukX+s2ADT+F+IIqCNXhbO0z+QsdoLrXp61mQctuefPw9Xz+Ej52Ht3S FT7wLbC+JHqQNw2vJ/n4m2HvL5iuJN568XKCFxRVHkaa+9MpZsmPRF1LxVabJfwBoi r9CnKPPaETVgiKM9YWg4re3yxOfLonXzCJABy384BhXt+zcgC8MKld4Sn8SOT+VSai lRKyNmtwxZloyQDh4BMyRl6jQzj8fACzFIo1aJk/D5w3FmQfAPGuhuNqOfxLn10sZk dqXVE2CnYoI8Q== From: Ard Biesheuvel To: linux@armlinux.org.uk Cc: linux-arm-kernel@lists.infradead.org, Ard Biesheuvel , Steven Rostedt , Sudeep Holla , Cristian Marussi , Nathan Chancellor , Nick Desaulniers , Arnd Bergmann , Linus Walleij , Masami Hiramatsu Subject: [PATCH v3 04/13] ARM: ftrace: avoid redundant loads or clobbering IP Date: Thu, 3 Feb 2022 09:21:55 +0100 Message-Id: <20220203082204.1176734-5-ardb@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220203082204.1176734-1-ardb@kernel.org> References: <20220203082204.1176734-1-ardb@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4052; h=from:subject; bh=FZEbuSgHaYWYJR7CBLSwWxcwsIaxd58F48DouMJwycU=; b=owEB7QES/pANAwAKAcNPIjmS2Y8kAcsmYgBh+5CaDk7Kk7QT1X09wyb0rOiyblXYkbAofS23wII/ 0OGL1iGJAbMEAAEKAB0WIQT72WJ8QGnJQhU3VynDTyI5ktmPJAUCYfuQmgAKCRDDTyI5ktmPJNOIDA CPQ38ll0USZbOzRWptYeCpwKLcV7D9IHXitl6DwHMDklW9IDptbqLasg9Ew4qj2UvffhjKv2lAPa6w +gn36LbX8z+B6RQ6JRO00sKrRvUrMAnaYZj237H9nh+viKi2opa+u1tPAEgUCd8kHLOKVD/z0W5U/d J88ly16BHdCpxHtzvSSw3/ifNY+rM78GyeSETwwZvMwbvwt2XdDNBe+6rXZaFNLO6TsMFthGRSlote ZI4BPW9fVdkidhasd1DyG1eJKmzjPPktHJwFMFwa85H9XXI8CSElVi+7CRinnjZJk/eR8DForcUWHE ZaI6axQJH6xzkO1icxruxf6Nivy+h1MfxuhRxFPT/0uSnfAVpseN/eBdgAZZA5/ExSzTukGsgdPLRK oHkYoJxQVNXPD11ZKWvBtkWGxl8H5ji7ssiJqhslPJZQMXO6iC8kjsjtFi48HssOXs3haGtsY9gGwP 6lVYp5fE/PW5t/GGUREBfHwfrdM1PXzpqrRc36X6yscN4= X-Developer-Key: i=ardb@kernel.org; a=openpgp; fpr=F43D03328115A198C90016883D200E9CA6329909 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220203_002226_373669_8AFB0044 X-CRM114-Status: GOOD ( 17.35 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Tweak the ftrace return paths to avoid redundant loads of SP, as well as unnecessary clobbering of IP. This also fixes the inconsistency of using MOV to perform a function return, which is sub-optimal on recent micro-architectures but more importantly, does not perform an interworking return, unlike compiler generated function returns in Thumb2 builds. Let's fix this by popping PC from the stack like most ordinary code does. Signed-off-by: Ard Biesheuvel Reviewed-by: Steven Rostedt (Google) --- arch/arm/kernel/entry-ftrace.S | 51 +++++++++----------- 1 file changed, 22 insertions(+), 29 deletions(-) diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S index 237d435e29aa..67548c38a567 100644 --- a/arch/arm/kernel/entry-ftrace.S +++ b/arch/arm/kernel/entry-ftrace.S @@ -22,10 +22,7 @@ * mcount can be thought of as a function called in the middle of a subroutine * call. As such, it needs to be transparent for both the caller and the * callee: the original lr needs to be restored when leaving mcount, and no - * registers should be clobbered. (In the __gnu_mcount_nc implementation, we - * clobber the ip register. This is OK because the ARM calling convention - * allows it to be clobbered in subroutines and doesn't use it to hold - * parameters.) + * registers should be clobbered. * * When using dynamic ftrace, we patch out the mcount call by a "add sp, #4" * instead of the __gnu_mcount_nc call (see arch/arm/kernel/ftrace.c). @@ -70,26 +67,25 @@ .macro __ftrace_regs_caller - sub sp, sp, #8 @ space for PC and CPSR OLD_R0, + str lr, [sp, #-8]! @ store LR as PC and make space for CPSR/OLD_R0, @ OLD_R0 will overwrite previous LR - add ip, sp, #12 @ move in IP the value of SP as it was - @ before the push {lr} of the mcount mechanism + ldr lr, [sp, #8] @ get previous LR - str lr, [sp, #0] @ store LR instead of PC + str r0, [sp, #8] @ write r0 as OLD_R0 over previous LR - ldr lr, [sp, #8] @ get previous LR + str lr, [sp, #-4]! @ store previous LR as LR - str r0, [sp, #8] @ write r0 as OLD_R0 over previous LR + add lr, sp, #16 @ move in LR the value of SP as it was + @ before the push {lr} of the mcount mechanism - stmdb sp!, {ip, lr} - stmdb sp!, {r0-r11, lr} + push {r0-r11, ip, lr} @ stack content at this point: @ 0 4 48 52 56 60 64 68 72 - @ R0 | R1 | ... | LR | SP + 4 | previous LR | LR | PSR | OLD_R0 | + @ R0 | R1 | ... | IP | SP + 4 | previous LR | LR | PSR | OLD_R0 | - mov r3, sp @ struct pt_regs* + mov r3, sp @ struct pt_regs* ldr r2, =function_trace_op ldr r2, [r2] @ pointer to the current @@ -112,11 +108,9 @@ ftrace_graph_regs_call: #endif @ pop saved regs - ldmia sp!, {r0-r12} @ restore r0 through r12 - ldr ip, [sp, #8] @ restore PC - ldr lr, [sp, #4] @ restore LR - ldr sp, [sp, #0] @ restore SP - mov pc, ip @ return + pop {r0-r11, ip, lr} @ restore r0 through r12 + ldr lr, [sp], #4 @ restore LR + ldr pc, [sp], #12 .endm #ifdef CONFIG_FUNCTION_GRAPH_TRACER @@ -132,11 +126,9 @@ ftrace_graph_regs_call: bl prepare_ftrace_return @ pop registers saved in ftrace_regs_caller - ldmia sp!, {r0-r12} @ restore r0 through r12 - ldr ip, [sp, #8] @ restore PC - ldr lr, [sp, #4] @ restore LR - ldr sp, [sp, #0] @ restore SP - mov pc, ip @ return + pop {r0-r11, ip, lr} @ restore r0 through r12 + ldr lr, [sp], #4 @ restore LR + ldr pc, [sp], #12 .endm #endif @@ -202,16 +194,17 @@ ftrace_graph_call\suffix: .endm .macro mcount_exit - ldmia sp!, {r0-r3, ip, lr} - ret ip + ldmia sp!, {r0-r3} + ldr lr, [sp, #4] + ldr pc, [sp], #8 .endm ENTRY(__gnu_mcount_nc) UNWIND(.fnstart) #ifdef CONFIG_DYNAMIC_FTRACE - mov ip, lr - ldmia sp!, {lr} - ret ip + push {lr} + ldr lr, [sp, #4] + ldr pc, [sp], #8 #else __mcount #endif -- 2.30.2 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel