Messages in this thread | | | Date | Thu, 21 Oct 2021 09:35:38 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH] [v3] tracing: use %ps format string to print symbols |
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On Tue, 19 Oct 2021 17:33:13 +0200 Arnd Bergmann <arnd@kernel.org> wrote:
> From: Arnd Bergmann <arnd@arndb.de> > > clang started warning about excessive stack usage in > hist_trigger_print_key() > > kernel/trace/trace_events_hist.c:4723:13: error: stack frame size (1336) exceeds limit (1024) in function 'hist_trigger_print_key' [-Werror,-Wframe-larger-than] > > The problem is that there are two 512-byte arrays on the stack if > hist_trigger_stacktrace_print() gets inlined. I don't think this has > changed in the past five years, but something probably changed the > inlining decisions made by the compiler, so the problem is now made > more obvious. > > Rather than printing the symbol names into separate buffers, it > seems we can simply use the special %ps format string modifier > to print the pointers symbolically and get rid of both buffers. > > Marking hist_trigger_stacktrace_print() would be a simpler > way of avoiding the warning, but that would not address the > excessive stack usage. > > Fixes: 69a0200c2e25 ("tracing: Add hist trigger support for stacktraces as keys") > Link: https://lore.kernel.org/all/20211015095704.49a99859@gandalf.local.home/ > Reviewed-by: Tom Zanussi <zanussi@kernel.org> > Tested-by: Tom Zanussi <zanussi@kernel.org> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Looks good to me.
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
BTW, there are other functions under kernel/trace still allocating "char str[KSYM_SYMBOL_LEN]". I guess those also should be changed if this is the stack usage issue, right?
Thank you,
> --- > Changes in v3: > - Fix 32-bit cast warning > > Changes in v2: > - Use %pS instead of %ps to include offset in third string > - add (void*) cast to avoid compile-time warnings > --- > kernel/trace/trace_events_hist.c | 15 +++++---------- > 1 file changed, 5 insertions(+), 10 deletions(-) > > diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c > index f01e442716e2..632386b73fc3 100644 > --- a/kernel/trace/trace_events_hist.c > +++ b/kernel/trace/trace_events_hist.c > @@ -4706,7 +4706,6 @@ static void hist_trigger_stacktrace_print(struct seq_file *m, > unsigned long *stacktrace_entries, > unsigned int max_entries) > { > - char str[KSYM_SYMBOL_LEN]; > unsigned int spaces = 8; > unsigned int i; > > @@ -4715,8 +4714,7 @@ static void hist_trigger_stacktrace_print(struct seq_file *m, > return; > > seq_printf(m, "%*c", 1 + spaces, ' '); > - sprint_symbol(str, stacktrace_entries[i]); > - seq_printf(m, "%s\n", str); > + seq_printf(m, "%pS\n", (void*)stacktrace_entries[i]); > } > } > > @@ -4726,7 +4724,6 @@ static void hist_trigger_print_key(struct seq_file *m, > struct tracing_map_elt *elt) > { > struct hist_field *key_field; > - char str[KSYM_SYMBOL_LEN]; > bool multiline = false; > const char *field_name; > unsigned int i; > @@ -4747,14 +4744,12 @@ static void hist_trigger_print_key(struct seq_file *m, > seq_printf(m, "%s: %llx", field_name, uval); > } else if (key_field->flags & HIST_FIELD_FL_SYM) { > uval = *(u64 *)(key + key_field->offset); > - sprint_symbol_no_offset(str, uval); > - seq_printf(m, "%s: [%llx] %-45s", field_name, > - uval, str); > + seq_printf(m, "%s: [%llx] %-45ps", field_name, > + uval, (void *)(uintptr_t)uval); > } else if (key_field->flags & HIST_FIELD_FL_SYM_OFFSET) { > uval = *(u64 *)(key + key_field->offset); > - sprint_symbol(str, uval); > - seq_printf(m, "%s: [%llx] %-55s", field_name, > - uval, str); > + seq_printf(m, "%s: [%llx] %-55pS", field_name, > + uval, (void *)(uintptr_t)uval); > } else if (key_field->flags & HIST_FIELD_FL_EXECNAME) { > struct hist_elt_data *elt_data = elt->private_data; > char *comm; > -- > 2.29.2 >
-- Masami Hiramatsu <mhiramat@kernel.org>
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