Discussion
As part of initialization Linux allocates memory store concatenated commandline arguments. Which were originally in 3 parts.
This involves counting the length of the strings with stripped surrounding whitespace (using some string utils), summing allocating the desired amount of memory in 2 chunks, copying the strings into place, possibly splices in the 3rd part or appending it after a " -- ", & remembers the length of the result.
Now I'll discuss memory allocation & panicking...
1/5?
... checks (via a helper) a flag for which helper it should to allocate the memory & calls it, carefully (via helpers) inserts an entry into a dynamic array of regions merging entries where possible, retries with more flexible parameters, & validates a MIRROR bitflag. If any of those approaches were successful it the memory-leak checks & any virtualization that everything's fine.
That allocation logic might carefully iterate over each free memrange looking for an appropriate entry to return.
3/
Or it performs similar logic iterating in reverse & rounding sizes down.
This memblock allocator may occasionally use a `kalloc` memory allocator, but I'll discuss that another day! For now...
One of those wrappers triggers a panic upon failure, crashing the system! Which has a wrapper to handle variadic args.
It crashes by ensuring a `panic_on_warn` flag's unset, disables IRQs & debugging features, carefully considers having another CPU core handle the crash (via a helper) & shuts down, ...
... grabs a lock, validates noone else is panicking, configures the loglevel to "motormouth" (lol!), increments a counter or runs CPU-specific code to break out of any spinlocks, formats & outputs the given error message with an added prefix, validates its state outputting any additional errors, ensures any GDB clients receive the remainder of the debug ringbuffer by triggering a CPU-specific breakpoint, possibly attempts to execute (via a helper) a crash image under lock, ...
5/6!
As mentioned that routine invokes a memory allocator. With extensive wrappers adding compiletime-debugging info, validation, tidier APIs, debugging & cleanliness, retries upon failing to achieve memory locality, & virtual memory translation.
The core logic here has a helper convert conditions into 1 of 3 flags, validates globals to see if its initialized & if not deferring to another allocator, if no alignment outputs (via a helper) an error message combining general & CPU-specific info, ...
2/