Messages in this thread | | | Date | Thu, 26 Nov 2015 09:29:32 +0800 | From | "Wangnan (F)" <> | Subject | Re: [PATCH] perf probe: Adjust dso->long_name for offline module |
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On 2015/11/26 9:10, 平松雅巳 / HIRAMATU,MASAMI 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=1 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 not 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/mymodule.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. However, >> user would expect it success in both case because perf is able to find >> 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, but >> this information is found from /proc/modules before it knows the real >> 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.
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