The Design and Implementation of the Anykernel and Rump Kernels

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sys/arch/x86/include/cpu.h:
#define curlwp
x86_curlwp()
sys/arch/sparc64/include/{cpu,param}.h (simplified for presentation):
#define curlwp
curcpu()->ci_curlwp
#define curcpu() (((struct cpu_info *)CPUINFO_VA)->ci_self)
#define CPUINFO_VA (KERNEND+0x018000)
#define KERNEND 0x0e0000000 /* end of kernel virtual space */
Figure 3.19: Comparison of curlwp definitions. The i386 port definition
results in a function symbol dereference, while the sparc64 port definition causes a
dereference to an absolute memory address.
For architectures which do not support the standard kernel ABI, we provide override
machine headers under the directory sys/rump/include/machine. This directory
is specified first in the include search path for rump kernel compilation, and therefore
headers contained in there override the NetBSD MD headers. Therefore, definitions
contained in the headers for that directory override the standard NetBSD definitions.
This way we can override problematic definitions in machine dependent code.
An example of what we consider problematic is SPARC64’s definition of curlwp,
which we previously illustrated in Figure 3.19. This approach allows us to support
rump kernels on all NetBSD architectures without having to write machine specific
counterparts or edit the existing MD interface definitions. The only negative
impact is that architectures which depend on override headers cannot use binary
kernel modules and must operate with the components compiled specifically for
rump kernels.
Lastly, the kernel module must be converted to the rump kernel symbol namespace
(Section 3.2.1) before linking. This conversion can be done with the objcopy tool
similar to what is done when components are built. However, using objcopy would
require generating another copy of the same module file. Instead of the objcopy
approach, we modified the module load path in sys/kern/subr_kobj.c to contain