I'm using KBUILD_OUTPUT to build my kernels. When I try to emerge nvidia-kernel, the kernel module has unresolved symbols. This is caused by conftest.sh failing to compile the test programs for remap_pfn_range and pci_get_class. This on the other hand is caused by asm/irq.h failing to include irq_vectors.h. The file is located in ${KBUILD_OUTPUT}/include2/asm/mach-default, but conftest.sh looks for it in ${KERNEL_SOURCE}/include/asm/mach-default.
Created attachment 71743 [details, diff] A patch that fixes the problem on my system.
Is this still an issue with the current releases of nvidia-drivers?
Reopen if you still have problems.