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 2FBA4C433F5 for ; Tue, 25 Jan 2022 15:51:20 +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=AGmPxn493J637xS0jcAxXqWIa/3O1gObulEtIloxi38=; b=UgI+MHrR8fVPkY qfzQ6tivJ9daDhHaUcPwzWGLQNTAIIH07XeP39cZu5Lk1/2YlSiZupgSRWp5AJrsgjxHobOSOuSy8 qBIT6aZe1Njb+XfaSQ0VrEbjKtzGVU/6fMKEnI4NbM2VUxPBYS4yNxIbFetkweqwFp83JJrXe6d+W XkgsblWSd5eBcuq218wZP32Zofq9B7lxYrXdut/J9NqzwRrJRp9N33qARMlQsUlMk5IXD/wQ3ldko p/Z1XeFhUr0Ns/1enZWwG9iukDyR8dFLkQaf/x+U3FckZKnVwczSyggn+1jW82OjUGyCkNn99/U6+ IWL7Ly4w3ZBEJ8eDtpPg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nCO4i-008T0s-6K; Tue, 25 Jan 2022 15:49:41 +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 1nCNso-008Q7N-Q1 for linux-arm-kernel@lists.infradead.org; Tue, 25 Jan 2022 15:37:24 +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 34C0D616C7; Tue, 25 Jan 2022 15:37:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 452E9C340E5; Tue, 25 Jan 2022 15:37:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1643125040; bh=vlKhqHRgXa/2PAAiHgYRPQ+moro6dzL/dC9QRAOQGV0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=j34F/SMqkg7f87Hz76A1cdUf3OhVCm2X1Pe/eGT21q/aepMutC78Geox8TKG0JLbx Zfg6P8LYhxIAmzTJOydOEWuhw5Ydx9r6Gs4B9mQ0ZsvWToJAOrBRekECVi2DQQ3XZ5 2eAu3r8IwN7fNKKDVJ2xVVGUvF1GNKC2ElaGiIXf6wRfoEgp8IbRiJmAOhHX9oEdWI a8NtTnctzIW00IQHxVpxWF7wIfWvRxHE+iOGqzYYocqQynQWanPPh0o3r6R5gEqU45 Zega0mi4pVIDa4bi1Noc3QPTjeju8OF6ZZMJxbvoEEdO0CI+VcNHW7R3CwMs1/WUqe Z/u4XoEtWpo6A== From: Ard Biesheuvel To: linux@armlinux.org.uk, linux-arm-kernel@lists.infradead.org Cc: Ard Biesheuvel , Arnd Bergmann , Linus Walleij , Nick Desaulniers Subject: [PATCH 4/8] ARM: ftrace: avoid redundant loads or clobbering IP Date: Tue, 25 Jan 2022 16:36:52 +0100 Message-Id: <20220125153656.1802079-5-ardb@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220125153656.1802079-1-ardb@kernel.org> References: <20220125153656.1802079-1-ardb@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3992; h=from:subject; bh=vlKhqHRgXa/2PAAiHgYRPQ+moro6dzL/dC9QRAOQGV0=; b=owEB7QES/pANAwAKAcNPIjmS2Y8kAcsmYgBh8BkQvWsbzE+mj9ZwyB2SWZq35jcLW9YwfrrKSjAU w5kVFz6JAbMEAAEKAB0WIQT72WJ8QGnJQhU3VynDTyI5ktmPJAUCYfAZEAAKCRDDTyI5ktmPJGB8DA C8zXsJBFN/SDYlreEhppQ6Advuh/wyM5v41T/H8apyJ5iO3g8w422ckctN8b+38U169gb2yAQKvCwY pVOkf53VAlkZwG0E3jnhsGuWlvZ6Q8iEW3qDGYdHqLiNwoSRf2ifxOrkdNIkiCyJd7rj6jsmAcs5gC d1KSvv5SyUxJ0zwBrXlLSkbSrU3ki75XGKiarfmbGwCdzeKOeSdqB1cFhnFdUhKLo3h71/msK0b1/G E74T6MFMlHQnnFOTVsLVATh9jNHcmali+HnLEkk7/sFVCkizvjy58j3li0YoFY8hDxZdaRM3F+C0BB Jdr3bf+amCqASrc4ZZLAfpGp0kVG4hbEE4ziptpavdTT00QQReyPgELrBOP3h8JvEFP92q+bMPwmzG s2IrGouZQD9fURCyoYC4BZbC7Aiv2gUsHFZ5N2pCJlo5eabrb1M+ARQn8piXw1GpEXrvweMQmO92R2 k2C2a7mC2U6vbjpOx1w+zyLCyx+YSRLvgJXOguS1PBXT0= 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-20220125_073722_980377_093759D8 X-CRM114-Status: GOOD ( 17.45 ) 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 --- 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