Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752826AbaAPNrN (ORCPT ); Thu, 16 Jan 2014 08:47:13 -0500 Received: from mail-vb0-f54.google.com ([209.85.212.54]:46795 "EHLO mail-vb0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752646AbaAPNrL (ORCPT ); Thu, 16 Jan 2014 08:47:11 -0500 MIME-Version: 1.0 In-Reply-To: <20140116125727.GI30257@mudshark.cambridge.arm.com> References: <1389869123-5884-1-git-send-email-jean.pihet@linaro.org> <20140116115634.GE30257@mudshark.cambridge.arm.com> <20140116125727.GI30257@mudshark.cambridge.arm.com> Date: Thu, 16 Jan 2014 14:47:10 +0100 Message-ID: Subject: Re: [PATCH] ARM64: perf: support dwarf unwinding in compat mode From: Jean Pihet To: Will Deacon Cc: "linux-kernel@vger.kernel.org" , "linaro-kernel@lists.linaro.org" , "linux-arm-kernel@lists.infradead.org" , Arnaldo , "patches@linaro.org" , Jiri Olsa , Ingo Molnar Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Will, On 16 January 2014 13:57, Will Deacon wrote: > On Thu, Jan 16, 2014 at 12:26:53PM +0000, Jean Pihet wrote: >> On 16 January 2014 12:56, Will Deacon wrote: >> > In your previous series, compat backtracing is actually split out into a >> > separate function (compat_user_backtrace), so it would be more consistent to >> > have a compat_user_stack_pointer macro, rather than add this check here. The compat_user_backtrace function is used to unwind using the frame pointer, it is not used to unwind using the dwarf info (which uses the user stack pointer). >> >> Do you mean this change instead? > > I don't think so... > >> diff --git a/kernel/events/internal.h b/kernel/events/internal.h >> index 569b2187..9b88d2e 100644 >> --- a/kernel/events/internal.h >> +++ b/kernel/events/internal.h >> @@ -185,7 +185,8 @@ static inline bool arch_perf_have_user_stack_dump(void) >> return true; >> } >> >> -#define perf_user_stack_pointer(regs) user_stack_pointer(regs) >> +#define perf_user_stack_pointer(regs) \ >> + (!compat_user_mode(regs)) ? ((regs)->sp) : ((regs)->compat_sp) > > This doesn't belong in core code; compat_user_mode and the fields of regs > are arm64-specific. Right. > So I suppose you need to rework your original patch to > call compat_user_stack_pointer (which we already define in compat.h for > arm64) if compat_user_mode(regs)). The perf core code calls perf_user_stack_pointer(regs) to retrieve the stack pointer, with perf_user_stack_pointer(regs) defined as user_stack_pointer(regs). The problem is that perf is not aware of the compat mode, so every arch has to implement user_stack_pointer(regs) correctly. For this reason I think the first patch proposal is the right one unless the perf core code is redesigned to handle different ABIs. Do you see a better implementation? > > The problem there is the inconsistency with respect to the regs argument: > > user_stack_pointer(regs) // Returns user stack pointer for regs > current_user_stack_pointer() // Returns current user stack pointer > compat_user_stack_pointer() // Doesn't take a regs argument! > > On top of that, x86 treats those last two functions differently when current > is a compat task. > > So the simplest thing would be to make compat_user_stack_pointer expand to > user_stack_pointer(current_pt_regs()) on arm64 and merge that in with your > original patch fixing user_stack_pointer. > > Will Thx! Jean -- 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/