From patchwork Fri Sep 26 11:54:13 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: AKASHI Takahiro X-Patchwork-Id: 4981891 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork1.web.kernel.org (Postfix) with ESMTP id B5F3B9F336 for ; Fri, 26 Sep 2014 11:57:12 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id AAF46201FE for ; Fri, 26 Sep 2014 11:57:11 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id AD1D9201BC for ; Fri, 26 Sep 2014 11:57:10 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1XXU7K-0006hr-9v; Fri, 26 Sep 2014 11:55:18 +0000 Received: from mail-pd0-f173.google.com ([209.85.192.173]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1XXU7H-0005Wk-4U for linux-arm-kernel@lists.infradead.org; Fri, 26 Sep 2014 11:55:16 +0000 Received: by mail-pd0-f173.google.com with SMTP id w10so3121069pde.32 for ; Fri, 26 Sep 2014 04:54:52 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=miv9DY96D27GMZpRemih5An0oTUjSwz7/Y4vK5nCny0=; b=mGAmGbngjYYisvFC6hQ+n1KoM/XUeESDKMBVeNvAZd1eizKbsolaZeSl8IUxq+NX44 UgsUxqm3tT4pl3Opy1lCoI3IEtQkbAt8ahY91TLegK5VX8zvAXhmGEPARbSvn9N/ddax sJ/6UQvq6tMUCxQFlW8gCLgRu+KeXPQf3dU6ISYhtQufHgO7GhbVIC+n6VJI9Tkp/NEg 34aa7DFwk0QH+rXXDyAbMZKRgQK2VKyiaw+0B7/LFeVXnNwFy376ctpyV+2YvAx32F7d jJQI2Ez2iGLu7SyzSQx2zAbi+3IS3VGr1XPhnyaerXIHronGPerJN45wLOvl/JFrKGgQ k2ZA== X-Gm-Message-State: ALoCoQnNnWo+RSunswYtyCRuAJRIeP9MU9VI0yA+hp+XDAyqrUqBjdavOR+1A9uJYS2TIb4wUj7y X-Received: by 10.70.123.136 with SMTP id ma8mr40028519pdb.139.1411732492546; Fri, 26 Sep 2014 04:54:52 -0700 (PDT) Received: from localhost.localdomain (KD182249092252.au-net.ne.jp. [182.249.92.252]) by mx.google.com with ESMTPSA id ps7sm4736288pbb.73.2014.09.26.04.54.47 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Fri, 26 Sep 2014 04:54:51 -0700 (PDT) From: AKASHI Takahiro To: catalin.marinas@arm.com, will.deacon@arm.com Subject: [RFC v2] arm64: kgdb: fix single stepping Date: Fri, 26 Sep 2014 20:54:13 +0900 Message-Id: <1411732453-5437-1-git-send-email-takahiro.akashi@linaro.org> X-Mailer: git-send-email 1.9.1 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20140926_045515_219100_C6D7893B X-CRM114-Status: GOOD ( 20.43 ) X-Spam-Score: -0.9 (/) Cc: linaro-kernel@lists.linaro.org, Vijaya.Kumar@caviumnetworks.com, linux-kernel@vger.kernel.org, AKASHI Takahiro , dsaxena@linaro.org, linux-arm-kernel@lists.infradead.org X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_NONE, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP I tried to verify kgdb in vanilla kernel on fast model, but it seems that the single stepping with kgdb doesn't work correctly since its first appearance at v3.15. On v3.15, 'stepi' command after breaking the kernel at some breakpoint steps forward to the next instruction, but the succeeding 'stepi' never goes beyond that. On v3.16, 'stepi' moves forward and stops at the next instruction just after enable_dbg in el1_dbg, and never goes beyond that. This variance of behavior seems to come in with the following patch in v3.16: commit 2a2830703a23 ("arm64: debug: avoid accessing mdscr_el1 on fault paths where possible") This patch (1) moves kgdb_disable_single_step() from 'c' command handling to single step handler. This makes sure that single stepping gets effective at every 's' command. Please note that, under the current implementation, single step bit in spsr, which is cleared by the first single stepping, will not be set again for the consecutive 's' commands because single step bit in mdscr is still kept on (that is, kernel_active_single_step() in kgdb_arch_handle_exception() is true). (2) removes 'enable_dbg' in el1_dbg. Single step bit in mdscr is turned on in do_handle_exception()-> kgdb_handle_expection() before returning to debugged context, and if debug exception is enabled in el1_dbg, we will see unexpected single- stepping in el1_dbg. (3) masks interrupts while single-stepping one instruction. If an interrupt is caught during processing a single-stepping, debug exception is unintentionally enabled by el1_irq's 'enable_dbg' before returning to debugged context. Thus, like in (2), we will see unexpected single-stepping in el1_irq. Basically (1) is for v3.15, (2) and (3) with (1) for v3.16. With those changes, we will see another problem if a breakpoint is set at interrupt-sensible places, like gic_handle_irq(): KGDB: re-enter error: breakpoint removed ffffffc000081258 ------------[ cut here ]------------ WARNING: CPU: 0 PID: 650 at kernel/debug/debug_core.c:435 kgdb_handle_exception+0x1dc/0x1f4() Modules linked in: CPU: 0 PID: 650 Comm: sh Not tainted 3.17.0-rc2+ #177 Call trace: [] dump_backtrace+0x0/0x130 [] show_stack+0x10/0x1c [] dump_stack+0x74/0xb8 [] warn_slowpath_common+0x8c/0xb4 [] warn_slowpath_null+0x14/0x20 [] kgdb_handle_exception+0x1d8/0x1f4 [] kgdb_brk_fn+0x18/0x28 [] brk_handler+0x9c/0xe8 [] do_debug_exception+0x3c/0xac Exception stack(0xffffffc07e027650 to 0xffffffc07e027770) ... [] el1_dbg+0x14/0x68 [] kgdb_cpu_enter+0x464/0x5c0 [] kgdb_handle_exception+0x190/0x1f4 [] kgdb_brk_fn+0x18/0x28 [] brk_handler+0x9c/0xe8 [] do_debug_exception+0x3c/0xac Exception stack(0xffffffc07e027ac0 to 0xffffffc07e027be0) ... [] el1_dbg+0x14/0x68 [] __handle_sysrq+0x11c/0x190 [] write_sysrq_trigger+0x4c/0x60 [] proc_reg_write+0x54/0x84 [] vfs_write+0x98/0x1c8 [] SyS_write+0x40/0xa0 Once some interrupt occurs, a breakpoint at gic_handle_irq() triggers kgdb. Kgdb then calls kgdb_roundup_cpus() to sync with other cpus. Current kgdb_roundup_cpus() unmasks interrupts temporarily to use smp_call_function(). This eventually allows another interrupt to occur and likely results in hitting a breakpoint at gic_handle_irq() again since debug exception is always enabled in el1_irq. We can avoid this issue by specifying "nokgdbroundup" in kernel parameter, but this will also leave other cpus be in unknown state in terms of kgdb, and may result in interfering with kgdb activity. Signed-off-by: AKASHI Takahiro --- arch/arm64/kernel/entry.S | 1 - arch/arm64/kernel/kgdb.c | 29 +++++++++++++++++++---------- 2 files changed, 19 insertions(+), 11 deletions(-) diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index fdd6eae..a935d5f 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -325,7 +325,6 @@ el1_dbg: mrs x0, far_el1 mov x2, sp // struct pt_regs bl do_debug_exception - enable_dbg kernel_exit 1 el1_inv: // TODO: add support for undefined instructions in kernel mode diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c index 75c9cf1..f1fc1d8 100644 --- a/arch/arm64/kernel/kgdb.c +++ b/arch/arm64/kernel/kgdb.c @@ -22,6 +22,7 @@ #include #include #include +#include #include struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] = { @@ -95,6 +96,8 @@ struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] = { { "fpcr", 4, -1 }, }; +static DEFINE_PER_CPU(unsigned int, kgdb_pstate); + char *dbg_get_reg(int regno, void *mem, struct pt_regs *regs) { if (regno >= DBG_MAX_REG_NUM || regno < 0) @@ -176,18 +179,14 @@ int kgdb_arch_handle_exception(int exception_vector, int signo, * over and over again. */ kgdb_arch_update_addr(linux_regs, remcom_in_buffer); - atomic_set(&kgdb_cpu_doing_single_step, -1); - kgdb_single_step = 0; - - /* - * Received continue command, disable single step - */ - if (kernel_active_single_step()) - kernel_disable_single_step(); err = 0; break; case 's': + /* mask interrupts while single stepping */ + __this_cpu_write(kgdb_pstate, linux_regs->pstate); + linux_regs->pstate |= (1 << 7); + /* * Update step address value with address passed * with step packet. @@ -198,8 +197,6 @@ int kgdb_arch_handle_exception(int exception_vector, int signo, */ kgdb_arch_update_addr(linux_regs, remcom_in_buffer); atomic_set(&kgdb_cpu_doing_single_step, raw_smp_processor_id()); - kgdb_single_step = 1; - /* * Enable single step handling */ @@ -229,6 +226,18 @@ static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned int esr) static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr) { + unsigned int pstate; + + kernel_disable_single_step(); + atomic_set(&kgdb_cpu_doing_single_step, -1); + + /* restore interrupt mask status */ + pstate = __this_cpu_read(kgdb_pstate); + if (pstate & (1 << 7)) + regs->pstate |= (1 << 7); + else + regs->pstate &= ~(1 << 7); + kgdb_handle_exception(1, SIGTRAP, 0, regs); return 0; }