Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751303AbbD3JAC (ORCPT ); Thu, 30 Apr 2015 05:00:02 -0400 Received: from foss.arm.com ([217.140.101.70]:35102 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751056AbbD3I7z (ORCPT ); Thu, 30 Apr 2015 04:59:55 -0400 Date: Thu, 30 Apr 2015 09:59:49 +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 Subject: Re: [PATCH] arm64: perf: Fix callchain parse error with kernel tracepoint events Message-ID: <20150430085949.GA32373@arm.com> References: <1430227248-19657-1-git-send-email-houpengyang@huawei.com> <20150429101234.GJ8236@arm.com> <55418A4D.5010900@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55418A4D.5010900@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: 2479 Lines: 51 On Thu, Apr 30, 2015 at 02:50:05AM +0100, Hou Pengyang wrote: > On 2015/4/29 18:12, Will Deacon wrote: > > On Tue, Apr 28, 2015 at 02:20:48PM +0100, Hou Pengyang wrote: > >> 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. > > > Hi, will, as you said, we can get fp by __builtin_frame_address() and > pstate by setting it to a static value. However, for sp, there isn't a > gcc builtin fuction like __builtin_stack_pointer, so assembly code is > needed. What's more, if CONFIG_FRAME_POINTER is close, can fp be got by > __builtin_frame_address()? Ah yes, I forgot the history of __builtin_stack_pointer (I think the LLVM guys proposed it and it was rejected by GCC). Anyway, we can use current_stack_pointer() instead. I don't think CONFIG_FRAME_POINTER is relevant here; if you don't have frame pointers then you won't be able to backtrace. The same issue happens with your proposed patch. 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/