Messages in this thread Patch in this message | | | Date | Thu, 24 Aug 2023 23:47:21 +0900 | From | Masami Hiramatsu (Google) <> | Subject | Re: [RFC PATCH v2 1/1] tracing/kprobes: Return EADDRNOTAVAIL when func matches several symbols |
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On Thu, 24 Aug 2023 16:31:13 +0200 Francis Laniel <flaniel@linux.microsoft.com> wrote:
> Hi. > > Le jeudi 24 août 2023, 15:02:27 CEST Masami Hiramatsu a écrit : > > On Thu, 24 Aug 2023 12:37:34 +0200 > > > > Francis Laniel <flaniel@linux.microsoft.com> wrote: > > > Previously to this commit, if func matches several symbols, a kprobe, > > > being > > > either sysfs or PMU, would only be installed for the first matching > > > address. This could lead to some misunderstanding when some BPF code was > > > never called because it was attached to a function which was indeed not > > > call, because the effectively called one has no kprobes. > > > > > > So, this commit returns EADDRNOTAVAIL when func matches several symbols. > > > This way, user needs to use addr to remove the ambiguity. > > > > Thanks for update the patch. I have some comments there. > > > > > Suggested-by: Masami Hiramatsu <mhiramat@kernel.org> > > > Signed-off-by: Francis Laniel <flaniel@linux.microsoft.com> > > > Link: > > > https://lore.kernel.org/lkml/20230819101105.b0c104ae4494a7d1f2eea742@kern > > > el.org/ --- > > > > > > kernel/trace/trace_kprobe.c | 42 +++++++++++++++++++++++++++++++++++++ > > > 1 file changed, 42 insertions(+) > > > > > > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c > > > index 23dba01831f7..0c8dd6ba650b 100644 > > > --- a/kernel/trace/trace_kprobe.c > > > +++ b/kernel/trace/trace_kprobe.c > > > @@ -705,6 +705,25 @@ static struct notifier_block trace_kprobe_module_nb = > > > {> > > > .priority = 1 /* Invoked after kprobe module callback */ > > > > > > }; > > > > > > +static int count_symbols(void *data, unsigned long unused) > > > +{ > > > + unsigned int *count = data; > > > + > > > + (*count)++; > > > + > > > + return 0; > > > +} > > > + > > > +static unsigned int func_name_several_symbols(char *func_name) > > > > If this returns boolean, please use 'bool' for return type. > > Also, I think 'func_name_is_unique()' is more natural. > > > > This name sounds better but it means it will check count == 1. > I am fine with it, but please see my below comment. > > > > +{ > > > + unsigned int count; > > > + > > > + count = 0; > > > + kallsyms_on_each_match_symbol(count_symbols, func_name, &count); > > > + > > > + return count > 1; > > > +} > > > + > > > > > > static int __trace_kprobe_create(int argc, const char *argv[]) > > > { > > > > > > /* > > > > > > @@ -836,6 +855,18 @@ static int __trace_kprobe_create(int argc, const char > > > *argv[])> > > > } > > > > > > } > > > > > > + /* > > > + * If user specifies KSYM, we check it does not correspond to several > > > + * symbols. > > > + * If this is the case, we return EADDRNOTAVAIL to indicate the user > > > + * he/she should use ADDR rather than KSYM to remove the ambiguity. > > > + */ > > > + if (symbol && func_name_several_symbols(symbol)) { > > > > Then, here will be > > > > if (symbol && !func_name_is_unique(symbol)) { > > > > I am fine with the above, but it means if users gives an unknown symbol, we > will return EADDRNOTAVAIL instead of currently returning ENOENT. > Is it OK?
Ah, good catch! Hm, then what about 'int number_of_same_symbols()' ?
if (symbol) { num = number_of_same_symbols(symbol); if (num > 1) return -EADDRNOTAVAIL; else if (num == 0) return -ENOENT; }
Thank you,
> > > > + ret = -EADDRNOTAVAIL; > > > + > > > + goto error; > > > + } > > > + > > > > > > trace_probe_log_set_index(0); > > > if (event) { > > > > > > ret = traceprobe_parse_event_name(&event, &group, gbuf, > > > > > > @@ -1699,6 +1730,7 @@ static int unregister_kprobe_event(struct > > > trace_kprobe *tk)> > > > } > > > > > > #ifdef CONFIG_PERF_EVENTS > > > > > > + > > > > > > /* create a trace_kprobe, but don't add it to global lists */ > > > struct trace_event_call * > > > create_local_trace_kprobe(char *func, void *addr, unsigned long offs, > > > > > > @@ -1709,6 +1741,16 @@ create_local_trace_kprobe(char *func, void *addr, > > > unsigned long offs,> > > > int ret; > > > char *event; > > > > > > + /* > > > + * If user specifies func, we check that function name does not > > > + * correspond to several symbols. > > > + * If this is the case, we return EADDRNOTAVAIL to indicate the user > > > + * he/she should use addr and offs rather than func to remove the > > > + * ambiguity. > > > + */ > > > + if (func && func_name_several_symbols(func)) > > > > Ditto. > > > > Thanks! > > > > > + return ERR_PTR(-EADDRNOTAVAIL); > > > + > > > > > > /* > > > > > > * local trace_kprobes are not added to dyn_event, so they are never > > > * searched in find_trace_kprobe(). Therefore, there is no concern of > > Best regards. > >
-- Masami Hiramatsu (Google) <mhiramat@kernel.org>
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