linux-kernel - Re: [PATCH] tracing/synthetic: use union instead of casts

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Date:   Tue, 08 Aug 2023 19:33:06 +0200
From:   Sven Schnelle <svens@...ux.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing/synthetic: use union instead of casts

Steven Rostedt <rostedt@...dmis.org> writes:

> The "dynamic" I was using wasn't about the fields were dynamic (union), but
> because the field the offset/len combo represents is of dynamic size. It's
> used all over the trace_events code.
>
> I would have in include/linux/trace_events.h (right above struct trace_entry):
>
> /* Used to find the offset and length of dynamic fields in trace events */
> struct trace_dynamic_info {
> #ifdef CONFIG_CPU_BIG_ENDIAN
> 	u16 offset;
> 	u16 len;
> #else
> 	u16 len;
> 	u16 offset;
> #endif
> };
>
> And then it kernel/trace/trace.h:
>
> union trace_synthetic_field {
> 	u8				as_u8;
> 	u16				as_u16;
> 	u32				as_u32;
> 	u64				as_u64;
> 	struct trace_dynamic_info	as_dynamic;
> };

Ok.

> I could work on the part of the trace_dynamic_info if you want.

Whatever you prefer. Should i update my patch and send it again, or do
you want to adjust it?

Thanks
Sven