gateway page is considered kernel space, we can panic when we should
only SIGSEGV. Hence, add the additional constraint that for page
faults we also require running with kernel privileges. The gateway
page is the only kernel code running with user privileges, iso this
is a correct way to exclude the gateway page from kernel land.
We do not currently exclude the gateway page for other faults as it
is not always the right way to do it. Further tuning will happen on
a case by case bases.
thr_create(2). This implementation is so far only compile tested.
But since this is also the last of the functions required to
support libthr, we're now functionally complete (for some weird
definition of functionally; and complete). Runtime testing can
commence.
sigreturn(), we cheat and assume the preserved registers are still
on-chip and unmodified. This is actually the case, but more by accident
than by design. We need to use unwinding eventually or explicitly
compile the kernel in a way that the compiler steers clear from using
the preserved registers completely.
o The SDM states that flushing the RSE in the cycle prior to the
call to ia32 code yields the best performance. We don't really
care to much about performance here, but we do the same anyway.
I'm being paranoia and conservative here.
o Only initialize the ia32 state registers, not the registers used
as scratch by the ia32 engine. This saves a couple of loads from
the trapframe, but also helps debugging: we don't clobber useful
debugging data (engineering hints :-)
o Make sure all general registers constituting ia32 state have been
initialized. If there's no useful to be loaded from the trapframe,
clear the register. This avoids accidentally leaking NaT bits.
o Make sure we set ar.k6 prior to clobbering ar.bspstore and also
set ar.k7 prior to setting sp. This fixes a race seen for ia64
native code as well (and previously fixed too).
backing store before we discard them. It is possible that we
enter the kernel (due to an execve in this case) with a lot of
dirty user registers and that the RSE has only partially spilled
them (to make room for new frames). We cannot move the backing
store pointer down (to discard user registers) when not all of
the user registers are on the backing store.
So, we flush the register stack IFF this happens. Unconditionally
doing the flush is too costly, because the condition in which we
need to flush is very rare.
This change appears to fix the SIGSEGV that sometimes happen for
newly executed processes and so far also appears to fix the last
of the corruption. It is possible, although not likely, that this
change prevents some other bug from happening, even though it is
itself not a fix. Hence the uncertainty. We'll know in a couple
of months I guess :-)
the stack to be changed in a way incompatible with elf32_map_insert()
where we used data_buf without initializing it for when the partial
mapping resulting in a misaligned image (typical when the page size
implied by the image is not the same as the page size in use by the
kernel). Since data_buf is passed by reference to vm_map_find(), the
compiler cannot warn about it.
While here, move all local variables to the top of the function.
