RE: [PATCH v5] kernel/trace: Add DISALLOW_TRACE_PRINTK make option

[David Laight]

From: Nicolas Boichat
> Sent: 24 August 2020 03:59
> 
> trace_printk is meant as a debugging tool, and should not be
> compiled into production code without specific debug Kconfig
> options enabled, or source code changes, as indicated by the
> warning that shows up on boot if any trace_printk is called:
>  **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
>  **                                                      **
>  ** trace_printk() being used. Allocating extra memory.  **
>  **                                                      **
>  ** This means that this is a DEBUG kernel and it is     **
>  ** unsafe for production use.                           **
> 
> If DISALLOW_TRACE_PRINTK=1 is passed on the make command
> line, the kernel will generate a build-time error if
> trace_printk is used. We expect distributors to set this
> option for their production kernels.
> 
> Note that the code to handle trace_printk is still present,
> so this does not prevent people from compiling out-of-tree
> kernel modules, or BPF programs.
> 
> Also, we are not making this a kernel config option as we
> want the developer convenience of being able to reuse a
> production kernel config, add trace_printk for debugging,
> and rebuild, without any config changes.

Since the objective seems to be to ensure there are no
calls to trace_printk() in the git tree, but to allow
them in uncommitted sources. Why not use a config option
and rely on rand-config builds to detect any 'accidental'
commits?

	David

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