From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754562AbcGTS2v (ORCPT ); Wed, 20 Jul 2016 14:28:51 -0400 Received: from mail-qt0-f177.google.com ([209.85.216.177]:36673 "EHLO mail-qt0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751576AbcGTS2q (ORCPT ); Wed, 20 Jul 2016 14:28:46 -0400 Subject: Re: [PATCH v15 08/10] arm64: Add trampoline code for kretprobes To: Catalin Marinas References: <1467995754-32508-1-git-send-email-dave.long@linaro.org> <1467995754-32508-9-git-send-email-dave.long@linaro.org> <20160719134655.GA21256@e104818-lin.cambridge.arm.com> Cc: Huang Shijie , James Morse , Marc Zyngier , Pratyush Anand , Sandeepa Prabhu , Will Deacon , William Cohen , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Steve Capper , Masami Hiramatsu , Li Bin , Jisheng Zhang , Mark Rutland , Daniel Thompson , Vladimir Murzin , Petr Mladek , Ard Biesheuvel , Jens Wiklander , Robin Murphy , Mark Brown , Suzuki K Poulose , Dave P Martin , Andrey Ryabinin , yalin wang , Yang Shi , Zi Shen Lim , John Blackwood , Andrew Morton , =?UTF-8?Q?Alex_Benn=c3=a9e?= , Adam Buchbinder , Christoffer Dall From: David Long Message-ID: <578FC2D7.9090708@linaro.org> Date: Wed, 20 Jul 2016 14:28:39 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <20160719134655.GA21256@e104818-lin.cambridge.arm.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/19/2016 09:46 AM, Catalin Marinas wrote: > On Fri, Jul 08, 2016 at 12:35:52PM -0400, David Long wrote: >> --- /dev/null >> +++ b/arch/arm64/kernel/probes/kprobes_trampoline.S >> @@ -0,0 +1,85 @@ >> +/* >> + * trampoline entry and return code for kretprobes. >> + */ >> + >> +#include >> +#include >> +#include >> + >> + .text >> + >> +.macro save_all_base_regs >> + stp x0, x1, [sp, #S_X0] >> + stp x2, x3, [sp, #S_X2] >> + stp x4, x5, [sp, #S_X4] >> + stp x6, x7, [sp, #S_X6] >> + stp x8, x9, [sp, #S_X8] >> + stp x10, x11, [sp, #S_X10] >> + stp x12, x13, [sp, #S_X12] >> + stp x14, x15, [sp, #S_X14] >> + stp x16, x17, [sp, #S_X16] >> + stp x18, x19, [sp, #S_X18] >> + stp x20, x21, [sp, #S_X20] >> + stp x22, x23, [sp, #S_X22] >> + stp x24, x25, [sp, #S_X24] >> + stp x26, x27, [sp, #S_X26] >> + stp x28, x29, [sp, #S_X28] >> + add x0, sp, #S_FRAME_SIZE >> + stp lr, x0, [sp, #S_LR] >> +/* >> + * Construct a useful saved PSTATE >> + */ >> + mrs x0, nzcv >> + and x0, x0, #(PSR_N_BIT | PSR_Z_BIT | PSR_C_BIT | PSR_V_BIT) >> + mrs x1, daif >> + and x1, x1, #(PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT) > > I don't think you need the masking here, the mrs should return the > corresponding 4 bits. > OK. I see you've done that. >> + orr x0, x0, x1 >> + mrs x1, CurrentEL >> + and x1, x1, #(3 << 2) >> + orr x0, x1, x0 >> + mrs x1, SPSel >> + and x1, x1, #1 > > Same here. OK. ^ > >> + orr x0, x1, x0 >> + str x0, [sp, #S_PSTATE] >> +.endm > > How is this pstate used, other than the restoring of the condition flag > in the restore_all_base_regs macro? Does a kretprobes handler need > access to them? > A kretprobes handler should probably be able to examine a reasonable pstate value, particularly in terms of DAIF. As I recall not having a valid DAIF was an issue at one time. > Anyway, it's worth doing an stp xzr, x0, [sp, S_PC] so that we > initialise the pc in pt_regs. > OK. Looks like you've done this. >> + >> +.macro restore_all_base_regs >> + ldr x0, [sp, #S_PSTATE] >> + and x0, x0, #(PSR_N_BIT | PSR_Z_BIT | PSR_C_BIT | PSR_V_BIT) >> + msr nzcv, x0 >> + ldp x0, x1, [sp, #S_X0] >> + ldp x2, x3, [sp, #S_X2] >> + ldp x4, x5, [sp, #S_X4] >> + ldp x6, x7, [sp, #S_X6] >> + ldp x8, x9, [sp, #S_X8] >> + ldp x10, x11, [sp, #S_X10] >> + ldp x12, x13, [sp, #S_X12] >> + ldp x14, x15, [sp, #S_X14] >> + ldp x16, x17, [sp, #S_X16] >> + ldp x18, x19, [sp, #S_X18] >> + ldp x20, x21, [sp, #S_X20] >> + ldp x22, x23, [sp, #S_X22] >> + ldp x24, x25, [sp, #S_X24] >> + ldp x26, x27, [sp, #S_X26] >> + ldp x28, x29, [sp, #S_X28] >> +.endm >> + >> +ENTRY(kretprobe_trampoline) >> + >> + sub sp, sp, #S_FRAME_SIZE >> + >> + save_all_base_regs >> + >> + mov x0, sp >> + bl trampoline_probe_handler >> + /* Replace trampoline address in lr with actual >> + orig_ret_addr return address. */ >> + mov lr, x0 >> + >> + restore_all_base_regs >> + >> + add sp, sp, #S_FRAME_SIZE >> + >> + ret >> + >> +ENDPROC(kretprobe_trampoline) > Thanks, -dl