Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422698AbbD2KMl (ORCPT ); Wed, 29 Apr 2015 06:12:41 -0400 Received: from foss.arm.com ([217.140.101.70]:60998 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031674AbbD2KMj (ORCPT ); Wed, 29 Apr 2015 06:12:39 -0400 Date: Wed, 29 Apr 2015 11:12:34 +0100 From: Will Deacon To: Hou Pengyang Cc: "a.p.zijlstra@chello.nl" , "paulus@samba.org" , "mingo@redhat.com" , "acme@kernel.org" , "wangnan0@huawei.com" , Catalin Marinas , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , mark.rutland@arm.com Subject: Re: [PATCH] arm64: perf: Fix callchain parse error with kernel tracepoint events Message-ID: <20150429101234.GJ8236@arm.com> References: <1430227248-19657-1-git-send-email-houpengyang@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1430227248-19657-1-git-send-email-houpengyang@huawei.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: 3492 Lines: 82 Hello, On Tue, Apr 28, 2015 at 02:20:48PM +0100, Hou Pengyang wrote: > For ARM64, when tracing with tracepoint events, the IP and cpsr are set > to 0, preventing the perf code parsing the callchain and resolving the > symbols correctly. > > ./perf record -e sched:sched_switch -g --call-graph dwarf ls > [ perf record: Captured and wrote 0.146 MB perf.data ] > ./perf report -f > Samples: 194 of event 'sched:sched_switch', Event count (approx.): 194 > Children Self Command Shared Object Symbol > 100.00% 100.00% ls [unknown] [.] 0000000000000000 > > The fix is to implement perf_arch_fetch_caller_regs for ARM64, which fills > several necessary registers used for callchain unwinding, including pc,sp, > fp and psr . > > With this patch, callchain can be parsed correctly as follows: > > ...... > + 2.63% 0.00% ls [kernel.kallsyms] [k] vfs_symlink > + 2.63% 0.00% ls [kernel.kallsyms] [k] follow_down > + 2.63% 0.00% ls [kernel.kallsyms] [k] pfkey_get > + 2.63% 0.00% ls [kernel.kallsyms] [k] do_execveat_common.isra.33 > - 2.63% 0.00% ls [kernel.kallsyms] [k] pfkey_send_policy_notify > pfkey_send_policy_notify > pfkey_get > v9fs_vfs_rename > page_follow_link_light > link_path_walk > el0_svc_naked > ....... > > For tracepoint event, stack parsing also doesn't work well for ARM. Jean Pihet > comed up a patch: > http://thread.gmane.org/gmane.linux.kernel/1734283/focus=1734280 Any chance you could revive that series too, please? I'd like to update both arm and arm64 together, since we're currently working at merging the two perf backends and introducing discrepencies is going to delay that even longer. > Signed-off-by: Hou Pengyang > --- > arch/arm64/include/asm/perf_event.h | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/arch/arm64/include/asm/perf_event.h b/arch/arm64/include/asm/perf_event.h > index d26d1d5..16a074f 100644 > --- a/arch/arm64/include/asm/perf_event.h > +++ b/arch/arm64/include/asm/perf_event.h > @@ -24,4 +24,20 @@ extern unsigned long perf_misc_flags(struct pt_regs *regs); > #define perf_misc_flags(regs) perf_misc_flags(regs) > #endif > > +#define perf_arch_fetch_caller_regs(regs, __ip) { \ > + unsigned long sp; \ > + __asm__ ("mov %[sp], sp\n" : [sp] "=r" (sp)); \ > + (regs)->pc = (__ip); \ > + __asm__ ( \ > + "str %[sp], %[_arm64_sp] \n\t" \ > + "str x29, %[_arm64_fp] \n\t" \ > + "mrs %[_arm64_cpsr], spsr_el1 \n\t" \ > + : [_arm64_sp] "=m" (regs->sp), \ > + [_arm64_fp] "=m" (regs->regs[29]), \ > + [_arm64_cpsr] "=r" (regs->pstate) \ Does this really all need to be in assembly code? Ideally we'd use something like __builtin_stack_pointer and __builtin_frame_pointer. That just leaves the CPSR, but given that it's (a) only used for user_mode_regs tests and (b) this macro is only used by ftrace, then we just set it to a static value indicating that we're at EL1. So I *think* we should be able to write this as three lines of C. Will -- 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/