| Message ID | 1448451059-156220-1-git-send-email-wangnan0@huawei.com |
|---|---|
| State | New |
| Headers | show |
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. -- 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/
On 2015/11/26 3:35, Arnaldo Carvalho de Melo wrote: > Em Wed, Nov 25, 2015 at 11:30:59AM +0000, Wang Nan escreveu: >> 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} >> # ./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 > Understood, since we are giving the path to that module, we can, if its > build-id matches the one for the online module, use it, is that the > case, i.e. do we check, int his scenario, that the build-id matches? Please see my test result in v2 patch [1]. In symsrc__init() build-id would be checked. [1] http://lkml.kernel.org/r/1448507949-187812-1-git-send-email-wangnan0@huawei.com # ./perf probe -m ./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 # ./perf probe -d '*' Removed event: probe:my_func # mv ./mymodule.{ko,.bak} # mv ./moduleb.ko mymodule.ko # ./perf probe -m ./mymodule.ko my_func /home/wangnan/kmodule/mymodule.ko 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 probe -v -m ./mymodule.ko my_func probe-definition(0): my_func symbol:my_funcfile:(null) line:0 offset:0 return:0 lazy:(null) 0 arguments Could not open debuginfo. Try to use symbols. symsrc__init: build id mismatch for /home/wangnan/kmodule/mymodule.ko. /home/wangnan/kmodule/mymodule.ko 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. Reason: No such file or directory (Code: -2) -- 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/
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c index 93996ec..ea4f79f 100644 --- a/tools/perf/util/probe-event.c +++ b/tools/perf/util/probe-event.c @@ -2516,6 +2516,7 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev, struct probe_trace_point *tp; int num_matched_functions; int ret, i, j, skipped = 0; + const char *dup_filename; map = get_target_map(pev->target, pev->uprobes); if (!map) { @@ -2523,6 +2524,21 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev, goto out; } + /* + * If the map's dso is an offline module, give dso__load() a chance + * to find the file path of that module by fixing long_name. + */ + if (map->dso && strchr(pev->target, '/')) { + if (!map->dso->long_name || map->dso->long_name[0] == '[') { + dup_filename = strdup(pev->target); + if (!dup_filename) { + ret = -ENOMEM; + goto out; + } + dso__set_long_name(map->dso, dup_filename, true); + } + } + syms = malloc(sizeof(struct symbol *) * probe_conf.max_probes); if (!syms) { ret = -ENOMEM;
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} # ./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. In another aspect, if dso__load() can get the offline module through buildid cache, it can read symble table from that ko. Even if debuginfo is not available, 'perf probe' can success if the '.symtab' can be found. This patch fixes long_name so dso__load() is able to find module's path and read symbol table in this case. After this patch: # rm -rf ~/.debug/ # mv /usr/lib64/elfutils/libebl_x86_64.so{,.bak} # ./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 # mv /usr/lib64/elfutils/libebl_x86_64.so{.bak,} Signed-off-by: Wang Nan <wangnan0@huawei.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Zefan Li <lizefan@huawei.com> Cc: pi3orama@163.com --- tools/perf/util/probe-event.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) -- 1.8.3.4 -- 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/