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

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Date:   Thu, 19 Dec 2019 18:33:49 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sven Schnelle <svens@...ux.ibm.com>
Cc:     linux-trace-devel@...r.kernel.org,
        Tom Zanussi <zanussi@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] ftrace: fix endianness bug in histogram trigger

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?

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-svens@linux.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++;
>  		}
>  	}