On Wed, 19 Mar 2025 14:34:19 +0000 Douglas Raillard <[email protected]> wrote:
> Hi, > > On 19-03-2025 12:18, Masami Hiramatsu (Google) wrote: > > Hi, > > > > On Tue, 18 Mar 2025 18:09:38 +0000 > > Douglas RAILLARD <[email protected]> wrote: > > > >> From: Douglas Raillard <[email protected]> > >> > >> The printk format for synth event uses "%.*s" to print string fields, > >> but then only passes the pointer part as var arg. > >> > >> Add the missing precision var arg. > > > > I'm not sure what you want to. Would you mean showing the string length too? > > But I think actual output(*) shows only string, right? > > > > (*) the output data which can be read from `trace` file. > > The "%.*s" printf/printk format specifier has 2 components: > 1. the "*" part that in printf documentation called the "precision" > 2. the "s" part that is called the "specifier" > > For a "s" specifier, the precision is interpreted as the number of chars to > display from that string. > In any case, using "*" as precision means the value is passed dynamically, as > a parameter to printf/printk, > before the actual char *. Both those args are consumed by printk to display > "%.*s", the precision is never > displayed on its own. > > In the current state, synthetic event use "%.*s" for string fields, but then > only a single `__get_str(field)` > is passed to printk, so it's missing the precision arg. Both trace-cmd and > our parser report an error because of that. > > The alternative would be to just use "%s" instead of "%.*s", but I assume > whoever wrote the code initially had a reason > to use the precision (maybe to print non-null-terminated strings ?), so I > simply fixed the arguments. Ah, got it. It seems that the first precision parameter is for limiting the length of the string according to the commit; https://lore.kernel.org/all/b6bdb34e70d970e8026daa3503db6b8e5cdad524.1601848695.git.zanu...@kernel.org/T/#u So, I think it should always print the STR_VAR_LEN_MAX value. Steve, can you check it? Thank you, > > > > > Thank you, > > > >> > >> Signed-off-by: Douglas Raillard <[email protected]> > >> --- > >> kernel/trace/trace_events_synth.c | 3 ++- > >> 1 file changed, 2 insertions(+), 1 deletion(-) > >> > >> diff --git a/kernel/trace/trace_events_synth.c > >> b/kernel/trace/trace_events_synth.c > >> index e3f7d09e5512..274b9b1d9f7d 100644 > >> --- a/kernel/trace/trace_events_synth.c > >> +++ b/kernel/trace/trace_events_synth.c > >> @@ -620,7 +620,8 @@ static int __set_synth_event_print_fmt(struct > >> synth_event *event, > >> if (event->fields[i]->is_string && > >> event->fields[i]->is_dynamic) > >> pos += snprintf(buf + pos, LEN_OR_ZERO, > >> - ", __get_str(%s)", event->fields[i]->name); > >> + ", (int)__get_dynamic_array_len(%s), > >> __get_str(%s)", > >> + event->fields[i]->name, event->fields[i]->name); > >> else if (event->fields[i]->is_stack) > >> pos += snprintf(buf + pos, LEN_OR_ZERO, > >> ", __get_stacktrace(%s)", > >> event->fields[i]->name); > >> -- > >> 2.43.0 > >> > -- Masami Hiramatsu (Google) <[email protected]>
