Re: [bug report] ASoC: SOF: avoid a NULL dereference with unsupported widgets

["Péter Ujfalusi" <peter.ujfalusi@linux.intel.com>]

On 01/04/2023 10:44, Dan Carpenter wrote:
> On Fri, Mar 31, 2023 at 10:14:11AM +0300, Péter Ujfalusi wrote:
>> if src_fw_module is NULL then the print will be:
>> source (efault) or sink sink.module.name widget weren't set up properly
>>
>> Guennadi is relying on some black magic in the printk system to handle
>> the printing instead of open coding.
> 
> I've done compiler related work and explored some weird aspect of the
> C language and I am so fascinated by this.  I would have thought it
> crashes before the function is called.  I cannot even imagine how black
> magic like this would work.

I think it is not a compiler magic, but kernel magic:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/vsprintf.c#n700

> Is there anyway I can test this?

You could, If you have a laptop which uses SOF and it is Intel 11th gen
or newer then you can switch it to IPC4 and install the opt-in v2.5
(which would need with 6.4 kernel).
Apply this patch to 6.3-rc (or 6.2) and boot up, but unpatched kernel
will NULL dereference, so you need to have a backup option.

https://github.com/thesofproject/sof-bin

The v2.5 is not there as a release,you need to fetch the repo and follow
the instructions.

Read the instruction in v2.5.x/README.md before attempting to use this
release.

Now that I look back at the patch, yes it is not obvious, but it is
doing a valid thing.

-- 
Péter