These only exist for inserting some debugging information which normally a
compiler would (could) take care of. CFI stands for Call Frame Information
and helps a debugger create a reliable backtrace through functions.
This has potential value for looking at the kernel with debuggers such as
GDB and NLKD and potential value inside the kernel itself when somebody
ports a DWARF unwinder to the kernel proper (DWARF is the debugging format
CFI is a part of) which google shows some are contemplating.
If you look at CFI_ADJUST_CFA_OFFSET you see it turn into an assembler
pesudo op that you could, as it advices, learn more about in info as.
You also see that without CONFIG_UNWIND_INFO, they turn into whitespace and
given that at least currently CONFIG_UNWIND_INFO is a dead config variable
you may conclude that it's currently fairly safe not too worry about them.
Robert Day tried to remove the macro defintions a while ago it seems so he
may have further information in the form of people telling him why they
wanted them to stay.
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