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 A08E5C433F5 for ; Tue, 25 Jan 2022 15:49:56 +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=maNChjdIE7Oo/qQnYUmvEiWZEUpn02cfpxWjBxgKoCM=; b=jQzZSXCFkrU5um 4ifxwX9Q8L4Ukp5ytloThm4Mop1qjc84nVCYkSOD9H8U2Y7zKyJnVazFa1pk5c4Jx/uVlYneBxbAe BIIt+URN1fGSpzWcG2nU/Gx5TTpvVMPtNB0H2fw3tVSFW3EhdK3L/FRrWDUNMpX3ANkknxxPIRMHf WPzctyd2dkg/arc2Fpc0F9quMxmvASCFTNwvk8qxs0QMhtN5WVC8wHo5hrUJtDUek8blIv3F/Xnml 36DwZaHNds6RbqecASOfwGKmUsbsWXkpdiTHQiqrm7NsTQxrg7LnVdzOkMUBQa72HntkgErAuHi9h 7nr7R5obwK7ntDyN7fIg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nCO3R-008Seh-Vq; Tue, 25 Jan 2022 15:48:23 +0000 Received: from ams.source.kernel.org ([145.40.68.75]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nCNsl-008Q68-Mk for linux-arm-kernel@lists.infradead.org; Tue, 25 Jan 2022 15:37:22 +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 ams.source.kernel.org (Postfix) with ESMTPS id 3F15BB81814; Tue, 25 Jan 2022 15:37:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 97A79C340E0; Tue, 25 Jan 2022 15:37:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1643125037; bh=w+Ohe/5Uwvj7OH6OluSj4f4+Q9qV6OIdWVe7f9ww/Z8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=QEjtdcC41l9S3HfYH+K11TVYRZ3JadhD9A7CPOdRdW6IAaQWSim6tMVOKBankUTOq 2dcX2ttO621lD6ORS57pD3oV/12MWtrpwr9s947gOWiicxvGh3/gT4fThXqUzgvf9D UNtS0XYnpPSseKC2UO0fHYr/eFhF8LWRryqCTFDJ9ycRLnVO5ayG90V7U6/rt0MK+v Rf/z9VMP+gCR5YWbDnnTdI2tVfrkVbbZ89jf6uzLGmBhKI8A9qUZoZnstfYo2veZR4 P4+ZTbHnPwIadtj5kXLmYlOBGUJsbn8KaBMQNcPSQ1zi8cG0UvflV3zoyWJHIVnisE S7RKL8Jf0Lw7A== 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 2/8] ARM: ftrace: use ADD not POP to counter PUSH at entry Date: Tue, 25 Jan 2022 16:36:50 +0100 Message-Id: <20220125153656.1802079-3-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=1748; h=from:subject; bh=w+Ohe/5Uwvj7OH6OluSj4f4+Q9qV6OIdWVe7f9ww/Z8=; b=owEB7QES/pANAwAKAcNPIjmS2Y8kAcsmYgBh8BkMQRpT3VKZWsEj3JJIN+2lRyR5mc4nMapAMIrA jLEDQKaJAbMEAAEKAB0WIQT72WJ8QGnJQhU3VynDTyI5ktmPJAUCYfAZDAAKCRDDTyI5ktmPJH5xC/ 41+MmUhS17WzSTjFqIJRcSdhi7Md5SzUxeyKjbR+zCXcwMpFXufTArnC4HiNWHvvkcmc1OMLcelLwq ykNdll95vLGZvGOmm1iJB11fNQhWD4PcZVgolm5sf929oMQ6qdeFApqxsPfCJKnUw5ZrxPkuEZ4Atn pq5tL5axxPy77Ax7EVepmA1k5+793Fqb6J81p4QxB3ZajUBJJGouuNZrxTJgxg9NYYdep0UQsl1IV4 ko2iwruHEmzyCWc8b4YvLCJaAPb3H7kbgwsNOOGEj5tAqcCH7YNBuF6ntLr83BtF/EW6z4sG/e/4Oj Yoa5cP9VPvJBAuntHp0jBsKUzFu/hhRltHDTmdXuGXVoehSMdBZ3dBsfp8kb7X7lFGtrTE/bVSYokn DLtNWvNtCLra9ootMRxzca+Wi25GKWn1k5bkwg3msp7S+xZk8X6ojWKM9JVJodtmD3pamNeN29TAT9 zuHw29s1vNnR2T7ky4bH3Syd7fWoNjnek0w1I8iKS/ykU= 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_073720_107463_6DC9278B X-CRM114-Status: GOOD ( 18.48 ) 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 The compiler emitted hook used for ftrace consists of a PUSH {LR} to preserve the link register, followed by a branch-and-link (BL) to __gnu_mount_nc. Dynamic ftrace patches away the latter to turn the combined sequence into a NOP, using a POP {LR} instruction. This is not necessary, since the link register does not get clobbered in this case, and simply adding #4 to the stack pointer is sufficient, and avoids a memory access that may take a few cycles to resolve depending on the micro-architecture. Signed-off-by: Ard Biesheuvel --- arch/arm/kernel/entry-ftrace.S | 2 +- arch/arm/kernel/ftrace.c | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S index f4886fb6e9ba..dca12a09322a 100644 --- a/arch/arm/kernel/entry-ftrace.S +++ b/arch/arm/kernel/entry-ftrace.S @@ -27,7 +27,7 @@ * allows it to be clobbered in subroutines and doesn't use it to hold * parameters.) * - * When using dynamic ftrace, we patch out the mcount call by a "pop {lr}" + * 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). */ diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c index a006585e1c09..db72d3a6522d 100644 --- a/arch/arm/kernel/ftrace.c +++ b/arch/arm/kernel/ftrace.c @@ -25,9 +25,9 @@ #include #ifdef CONFIG_THUMB2_KERNEL -#define NOP 0xf85deb04 /* pop.w {lr} */ +#define NOP 0xf10d0d04 /* add.w sp, sp, #4 */ #else -#define NOP 0xe8bd4000 /* pop {lr} */ +#define NOP 0xe28dd004 /* add sp, sp, #4 */ #endif #ifdef CONFIG_DYNAMIC_FTRACE -- 2.30.2 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel