Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754681AbbGaOPs (ORCPT ); Fri, 31 Jul 2015 10:15:48 -0400 Received: from foss.arm.com ([217.140.101.70]:45350 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753337AbbGaOPq (ORCPT ); Fri, 31 Jul 2015 10:15:46 -0400 Date: Fri, 31 Jul 2015 15:15:41 +0100 From: Catalin Marinas To: William Cohen Cc: Steve Capper , David Long , "Jon Medhurst (Tixy)" , Russell King , Ananth N Mavinakayanahalli , Will Deacon , "linux-kernel@vger.kernel.org" , Anil S Keshavamurthy , Masami Hiramatsu , Mark Brown , sandeepa.s.prabhu@gmail.com, David Miller , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v7 5/7] arm64: Add trampoline code for kretprobes Message-ID: <20150731141540.GQ407@e104818-lin.cambridge.arm.com> References: <1434395229-6654-1-git-send-email-dave.long@linaro.org> <1434395229-6654-6-git-send-email-dave.long@linaro.org> <55918B68.7030900@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55918B68.7030900@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3443 Lines: 70 On Mon, Jun 29, 2015 at 02:16:08PM -0400, William Cohen wrote: > On 06/29/2015 01:25 PM, Steve Capper wrote: > > On 15 June 2015 at 20:07, David Long wrote: > >> diff --git a/arch/arm64/kernel/kprobes-arm64.h b/arch/arm64/kernel/kprobes-arm64.h > >> index ff8a55f..bdcfa62 100644 > >> --- a/arch/arm64/kernel/kprobes-arm64.h > >> +++ b/arch/arm64/kernel/kprobes-arm64.h > >> @@ -27,4 +27,45 @@ extern kprobes_pstate_check_t * const kprobe_condition_checks[16]; > >> enum kprobe_insn __kprobes > >> arm_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi); > >> > >> +#define SAVE_REGS_STRING\ > >> + " stp x0, x1, [sp, #16 * 0]\n" \ > >> + " stp x2, x3, [sp, #16 * 1]\n" \ > >> + " stp x4, x5, [sp, #16 * 2]\n" \ > >> + " stp x6, x7, [sp, #16 * 3]\n" \ > >> + " stp x8, x9, [sp, #16 * 4]\n" \ > >> + " stp x10, x11, [sp, #16 * 5]\n" \ > >> + " stp x12, x13, [sp, #16 * 6]\n" \ > >> + " stp x14, x15, [sp, #16 * 7]\n" \ > >> + " stp x16, x17, [sp, #16 * 8]\n" \ > >> + " stp x18, x19, [sp, #16 * 9]\n" \ > >> + " stp x20, x21, [sp, #16 * 10]\n" \ > >> + " stp x22, x23, [sp, #16 * 11]\n" \ > >> + " stp x24, x25, [sp, #16 * 12]\n" \ > >> + " stp x26, x27, [sp, #16 * 13]\n" \ > >> + " stp x28, x29, [sp, #16 * 14]\n" \ > >> + " str x30, [sp, #16 * 15]\n" \ > >> + " mrs x0, nzcv\n" \ > >> + " str x0, [sp, #8 * 33]\n" > >> + > >> + > >> +#define RESTORE_REGS_STRING\ > >> + " ldr x0, [sp, #8 * 33]\n" \ > >> + " msr nzcv, x0\n" \ > >> + " ldp x0, x1, [sp, #16 * 0]\n" \ > >> + " ldp x2, x3, [sp, #16 * 1]\n" \ > >> + " ldp x4, x5, [sp, #16 * 2]\n" \ > >> + " ldp x6, x7, [sp, #16 * 3]\n" \ > >> + " ldp x8, x9, [sp, #16 * 4]\n" \ > >> + " ldp x10, x11, [sp, #16 * 5]\n" \ > >> + " ldp x12, x13, [sp, #16 * 6]\n" \ > >> + " ldp x14, x15, [sp, #16 * 7]\n" \ > >> + " ldp x16, x17, [sp, #16 * 8]\n" \ > >> + " ldp x18, x19, [sp, #16 * 9]\n" \ > >> + " ldp x20, x21, [sp, #16 * 10]\n" \ > >> + " ldp x22, x23, [sp, #16 * 11]\n" \ > >> + " ldp x24, x25, [sp, #16 * 12]\n" \ > >> + " ldp x26, x27, [sp, #16 * 13]\n" \ > >> + " ldp x28, x29, [sp, #16 * 14]\n" \ > >> + " ldr x30, [sp, #16 * 15]\n" > > > > Do we need to restore x19..x28 as they are callee-saved? > > The goal was to make the trampoline not affect the values in any of > the registers, so if the calling conventions ever change the code will > still work. Figured it was safer and clearer just to save everything > rather than assuming that the compiler's code generated for > trampoline_probe_handler is going to save certain registers. If the PCS ever changes, we have other issues like cpu_switch_to(). So it's safe to assume that x19..x29 are callee-saved. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/