From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Wangnan (F)" Subject: Re: [PATCH] perf probe: Adjust dso->long_name for offline module Date: Thu, 26 Nov 2015 09:29:32 +0800 Message-ID: <5656607C.40907@huawei.com> References: <1448451059-156220-1-git-send-email-wangnan0@huawei.com> <50399556C9727B4D88A595C8584AAB3752631912@GSjpTKYDCembx32.service.hitachi.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from szxga02-in.huawei.com ([119.145.14.65]:59225 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751349AbbKZB3z (ORCPT ); Wed, 25 Nov 2015 20:29:55 -0500 In-Reply-To: <50399556C9727B4D88A595C8584AAB3752631912@GSjpTKYDCembx32.service.hitachi.net> Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: =?UTF-8?B?5bmz5p2+6ZuF5bezIC8gSElSQU1BVFXvvIxNQVNBTUk=?= , "acme@kernel.org" Cc: "linux-perf-users@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Arnaldo Carvalho de Melo , Namhyung Kim , Zefan Li , "pi3orama@163.com" On 2015/11/26 9:10, =E5=B9=B3=E6=9D=BE=E9=9B=85=E5=B7=B3 / HIRAMATU=EF=BC= =8CMASAMI wrote: > From: Wang Nan [mailto:wangnan0@huawei.com] >> If libelf unable to open debuginfo for an offline module but the ko = has >> symtab, something unexpected may happen. >> >> # rm -rf ~/.debug/ >> # mv /usr/lib64/elfutils/libebl_x86_64.so{,.bak} > Please do give more possible usecase. removing libebl is crazy, > and broken environment. It is a real problem we met, where perf itself is statically linked and copied to target platform. > If you'd like to use perf probe without debuginfo, make NO_DWARF=3D1 = or > strip the target binary. Can't simply stripping the target binary because the symtab would also be stipped out. >> # ./perf probe -m /home/wangnan/kmodule/mymodule.ko my_func >> [mymodule] with build id 326ab42550ef3d24944f53c817533728367effeb no= t found, continuing without symbols >> Failed to find symbol my_func in /home/wangnan/kmodule/mymodule.ko >> Error: Failed to add events >> # ./perf buildid-cache -a ./mymodule.ko >> # ./perf probe -m /home/wangnan/kmodule/mymodule.ko my_func >> Added new event: >> probe:my_func (on my_func in /home/wangnan/kmodule/mymodul= e.ko) >> >> You can now use it in all perf tools, such as: >> >> perf record -e probe:my_func -aR sleep 1 >> >> In the above example, probe fails if it isn't in buildid-cache. Howe= ver, >> user would expect it success in both case because perf is able to fi= nd >> probe points actually. >> >> The problem is because perf won't utilize module's full path if it >> failed to open debuginfo. In >> convert_to_probe_trace_events -> >> find_probe_trace_events_from_map -> >> get_target_map -> >> kernel_get_module_map -> >> machine__findnew_module_map -> >> map_groups__find_by_name >> >> map_groups__find_by_name() is able to find the map of that module, b= ut >> this information is found from /proc/modules before it knows the rea= l >> path of the offline module. Therefore, the map->dso->long_name is >> set to something like '[mymodule]', which prevents dso__load() find >> the real path of the module file. > Hmm, if so, it should be fixed in map or machine, not in probe-event.= c. Will do in next version. Thank you.