linux-kernel - Re: [PATCH 3/3] ftrace: fix endianness bug in histogram trigger

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Date:   Fri, 20 Dec 2019 09:25:10 -0600
From:   Tom Zanussi <zanussi@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Sven Schnelle <svens@...ux.ibm.com>
Cc:     linux-trace-devel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] ftrace: fix endianness bug in histogram trigger

Hi Steve,

On Thu, 2019-12-19 at 18:33 -0500, Steven Rostedt wrote:
> On Wed, 18 Dec 2019 08:44:27 +0100
> Sven Schnelle <svens@...ux.ibm.com> wrote:
> 
> > At least on PA-RISC and s390 synthetic histogram triggers are
> > failing
> > selftests because trace_event_raw_event_synth() always writes a 64
> > bit
> > values, but the reader expects a field->size sized value. On little
> > endian
> > machines this doesn't hurt, but on big endian this makes the reader
> > always
> > read zero values.
> 
> Tom,
> 
> Does this patch look fine to you?

Yeah, it looks fine to me.

Acked-by: Tom Zanussi <tom.zanussi@...ux.intel.com>

> 
> Also, it was only sent to linux-trace-devel. You can see the original
> patch here:
> 
>   https://lore.kernel.org/linux-trace-devel/20191218074427.96184-4-sv
> ens@...ux.ibm.com/
> 
> -- Steve
> 
> 
> > 
> > Signed-off-by: Sven Schnelle <svens@...ux.ibm.com>
> > ---
> >  kernel/trace/trace_events_hist.c | 21 ++++++++++++++++++++-
> >  1 file changed, 20 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/trace/trace_events_hist.c
> > b/kernel/trace/trace_events_hist.c
> > index f49d1a36d3ae..f62de5f43e79 100644
> > --- a/kernel/trace/trace_events_hist.c
> > +++ b/kernel/trace/trace_events_hist.c
> > @@ -911,7 +911,26 @@ static notrace void
> > trace_event_raw_event_synth(void *__data,
> >  			strscpy(str_field, str_val,
> > STR_VAR_LEN_MAX);
> >  			n_u64 += STR_VAR_LEN_MAX / sizeof(u64);
> >  		} else {
> > -			entry->fields[n_u64] =
> > var_ref_vals[var_ref_idx + i];
> > +			struct synth_field *field = event-
> > >fields[i];
> > +			u64 val = var_ref_vals[var_ref_idx + i];
> > +
> > +			switch (field->size) {
> > +			case 1:
> > +				*(u8 *)&entry->fields[n_u64] =
> > (u8)val;
> > +				break;
> > +
> > +			case 2:
> > +				*(u16 *)&entry->fields[n_u64] =
> > (u16)val;
> > +				break;
> > +
> > +			case 4:
> > +				*(u32 *)&entry->fields[n_u64] =
> > (u32)val;
> > +				break;
> > +
> > +			default:
> > +				entry->fields[n_u64] = val;
> > +				break;
> > +			}
> >  			n_u64++;
> >  		}
> >  	}
> 
>