Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752221AbaBCP2J (ORCPT ); Mon, 3 Feb 2014 10:28:09 -0500 Received: from mail-ve0-f181.google.com ([209.85.128.181]:38400 "EHLO mail-ve0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750967AbaBCP2H (ORCPT ); Mon, 3 Feb 2014 10:28:07 -0500 MIME-Version: 1.0 In-Reply-To: References: <1390252922-25889-1-git-send-email-jean.pihet@linaro.org> Date: Mon, 3 Feb 2014 16:28:06 +0100 Message-ID: Subject: Re: [Libunwind-devel] [RFC PATCH 0/3] Add support for dwarf compat mode unwinding From: Jean Pihet To: Arun Sharma , Jiri Olsa , Arnaldo Carvalho de Melo Cc: Will Deacon , "linux-kernel@vger.kernel.org" , libunwind-devel 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 Arun, On 22 January 2014 06:15, Arun Sharma wrote: > On Tue, Jan 21, 2014 at 12:16 AM, Jean Pihet wrote: > >>>> This is the case when e.g. profiling an ARMv7 binary that runs on an >>>> ARMv8 (aka AARCH64) platform. >>> >>> Why not configure libunwind for ARMv7 in that case? >>> >>> I'm trying to understand how is your use case different from using >>> x86_32 libunwind to do local unwinding on a x86_64 machine. >> Can you give more details on the use case and how to configure >> libunwind? > > You could either build libunwind on a ARMv7 machine and copy it over > or setup a 32 bit chroot on a 64 bit kernel and compile libunwind > inside that. > >> The provided patches dynamically detect the target binary >> address size and parse the debug info accordingly, all that in a >> single library. > > This is generally called cross-unwinding in libunwind lingo. Some > description here: > > http://www.nongnu.org/libunwind/man/libunwind%283%29.html#section_4 > >> >> Note: my use case is to call libunwind from the perf utility in order >> to unwind from the dwarf info. >> > > You could link in two copies of libunwind into the perf binary: > * libunwind.a for local (host == target) unwinding > * libunwind-arm.a for 32 bit cross-unwinding > > Doing cross-unwinding requires you to write a bunch of "accessors" on > how to access the address space of a non-local thread. > > Something like ./configure --target=arm on aarch64. Thanks for the link and info. Is there a concrete example of cross-unwinding with multiple targets, for example on x86_64 using native and x86_32 libunwind libraries simultaneously? I am trying to assess the impact of multiple unwinding libs in the perf code. Jiri, Arnaldo, How is that done on x86? I do not think this can be done with the current perf code, am I correct? > > -Arun Regards, 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/