Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752149AbaAQJAO (ORCPT ); Fri, 17 Jan 2014 04:00:14 -0500 Received: from mail-vb0-f43.google.com ([209.85.212.43]:55384 "EHLO mail-vb0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751331AbaAQJAK (ORCPT ); Fri, 17 Jan 2014 04:00:10 -0500 MIME-Version: 1.0 In-Reply-To: References: <1389869123-5884-1-git-send-email-jean.pihet@linaro.org> <20140116115634.GE30257@mudshark.cambridge.arm.com> <20140116125727.GI30257@mudshark.cambridge.arm.com> Date: Fri, 17 Jan 2014 10:00:09 +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 Hi Will, Some more thoughts below On 16 January 2014 14:47, Jean Pihet wrote: > 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. I see 2 issues in your proposal: 1) user_stack_pointer(regs) calls compat_user_stack_pointer if compat_user_mode(regs)) and compat_user_stack_pointer expands to user_stack_pointer. I see a circular dependency in the macros. 2) current_pt_regs() returns the current task regs although perf passes a regs struct that had been recorded previously. Am I missing something? Thx, Jean >> >> 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/