Re: [PATCH v2] libtraceevent: Handle parsing of "(REC)->" case

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 9 Jun 2021 07:43:08 +0200 (CEST)
Julia Lawall <julia.lawall@inria.fr> wrote:

> > If a trace event wraps the special __entry variable to dereference it with
> > parenthesis, it shows up in the trace event format file wrapping the
> > "(REC)" as well. For example, the "func_repeats" event passed the __entry
> > into a helper macro in the TP_printk() portion, and the macro correctly
> > wrapped its parameter in parenthesis. This caused the output to show:
> >
> >  "(((u64)(REC)->top_delta_ts << 32) | (REC)->bottom_delta_ts)"
> >
> > The parser then failed to parse the "(REC)->" portion, as it expected the
> > "->" to appear directly after the "REC". This is not a requirement, and
> > the parser should be able to handle such cases.
> >
> > When this occurred, trace-cmd would error with the following message:
> >
> > trace-cmd: No such file or directory
> >   Error: expected type 4 but read 5  
> 
> For the record, I have tried tracing two programs with Linux v5.13-rc4 or
> rc5 and both of them had this problem, while they didn't have this problem
> when traced with the same arguments with earlier Linux versions.  So it
> may be systematic for Linux v5.13.

The event mentioned in the change log was added in 5.13. But it is a valid
pattern, and not a bug in the 5.13 kernel.

-- Steve