[Qemu-devel] exec: About DISAS_JUMP and DISAS_UPDATE

[Sergey Fedorov <serge.fdrv@gmail.com>]

Hi all,

I am trying to understand what the difference should be between
DISAS_JUMP and DISAS_UPDATE. Actually, these macros have comments in
include/exec/exec-all.h which say that DISAS_JUMP should be used when
only PC was modified dynamically whereas DISAS_UPDATE should be used
when some other CPU state was (in addition to PC?) modified dynamically.
In fact, every target except ARM AArch64 does not distinguish between
them. As I can see ARM AArch64 seems to suppose that: (1) PC was not
modified when DISAS_UPDATE is used and should be updated with dc->pc
when finishing translation; (2) DISAS_JUMP can be used to indicate that
a new PC value was set and it should be preserved when finishing
translation.

So I'm a bit confused... What the difference should be? Maybe something
should be fixed/clarified to make the comments and the code consistent.

Best regards,
Sergey