On machines that run vanilla kernel-4.3.0 just fine, I do 'make oldconfig' in the kernel-4.4-rc? source and select the defaults for all new choices. The newly compiled kernel will crash at boot on any system I have. (No ultra modern stuff.) There seem to be two different cases/bugs. On my laptops (Dell Inspiron 4100 and 510m, Intel ICH4/5 chipset) it will print up to 'Thermal Zone THM[..]', then wait half a minute or so, then print 'Battery Slot [BAT0] (battery absent)' and 'Battery Slot [BAT1] (battery absent)' and wait again a long time. Then it proceeds into a stackdump and crashes. They don't have a sufficiently higher video mode to read relevant lines above the dump. Interestingly it says 'battery absent' in the machine that does have a working battery. It waits but prints nothing on the machine that doesn't have a battery. On an HP desktop (xw4300 workstation, Intel ICH7 chips) it seems to quickly run past that point and then panics with 'cannot open root device'. It doesn't seem to know about hda or sda. It suggest available options only as ram0 to ram15.
(In reply to Wim Osterholt from comment #0) > On machines that run vanilla kernel-4.3.0 just fine, .... The newly released Kernel-4.4-rc4 boots somewhat further on my Inspiron 4100. (Other machines not yet tested.) Now it crashes at the same spot where desktops also crashes: 'cannot open root fs'. It does not recognize any harddisk. I still haven't found a machine that actually can run a 4.4-kernel. For what kind of hardware you are developing this kernel?
It appears that make oldconfig from 4.3 -> 4.4-rc1 -> rc2 -> rc3 -> rc4 is a dangerous way to go. When I do make oldconfig from a 4.3 config file directly tot 4.4-rc4, then I get a dozen differences, like CONFIG_IDE=y where is was CONFIG_IDE=m. Anyway, both laptops now run kernel-4.4-rc4 and so do two desktops. The problems seems to be solved.