when _syserrno() fails to map a plan9 error string to
a unix error number, we copy the plan9 error string
to the per process error buffer "plan9err" and set
errno = EPLAN9.
when strerror() is called with EPLAN9, it returns
a pointer to the plan9err buffer.
amd64 passes first argument in RARG (BP) register
which has the be preserved duing _profin() and
_profout() calls. to handle this we introduce
_saveret() and _savearg(). _saveret() returns
AX, _savearg() returns RARG (BP). for archs other
and amd64, _saveret() and _savearg() are the
same function, doing nothing.
restoing works with dummy function:
uintptr
_restore(uintptr, uintptr ret)
{
return ret;
}
...
ret = _saveret();
arg = _savearg();
...
return _restore(arg, ret);
as we pass arg as the first argument, RARG (BP) is
restored.
semaphore locks have much higher overhead than initially presented
in the "Semaphores in Plan9" paper. until the reason for it has been
found out i will revert the changes.
store errno on the private process stack so its always per process
and not just per memory space. errno itself becomes a macro
dereferencing int *_errnoloc; which is initialized from main9.s
pointing to the private stack location.
various fixes in programs that just imported errno variable with
"extern int errno;" instead of including <errno.h>.
