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
