Compiling kernel but doesn't build kernel modules

I ran into the same problem! After googling around for a good while, it finally turned out (in my case) that the kernel build toolchain is very picky about some env options, as pointed out here.

Here, in my ~/.bashrc I had export GREP_OPTIONS='--color=always' and that seems to be causing problem with the module script generation.

So changing it to export GREP_OPTIONS='--color=auto' or export GREP_OPTIONS='--color=never' AND logging out/in solved the problem!

When GREP_OPTIONS='--color=always' used:

$ make clean modules SUBDIRS=drivers/staging/usbip
  CLEAN   drivers/staging/usbip/.tmp_versions
  CLEAN   drivers/staging/usbip/Module.symvers
  LD      drivers/staging/usbip/built-in.o
  CC [M]  drivers/staging/usbip/usbip_common.o
  CC [M]  drivers/staging/usbip/usbip_event.o
  CC [M]  drivers/staging/usbip/stub_dev.o
  CC [M]  drivers/staging/usbip/stub_main.o
  CC [M]  drivers/staging/usbip/stub_rx.o
  CC [M]  drivers/staging/usbip/stub_tx.o
  CC [M]  drivers/staging/usbip/vhci_sysfs.o
  CC [M]  drivers/staging/usbip/vhci_tx.o
  CC [M]  drivers/staging/usbip/vhci_rx.o
  CC [M]  drivers/staging/usbip/vhci_hcd.o
  LD [M]  drivers/staging/usbip/usbip-core.o
  LD [M]  drivers/staging/usbip/vhci-hcd.o
  LD [M]  drivers/staging/usbip/usbip-host.o
  Building modules, stage 2.
  MODPOST 0 modules

Changing to GREP_OPTIONS='--color=auto' and logging out/in:

$ make clean modules SUBDIRS=drivers/staging/usbip
  CLEAN   drivers/staging/usbip/.tmp_versions
  CLEAN   drivers/staging/usbip/Module.symvers
  LD      drivers/staging/usbip/built-in.o
  CC [M]  drivers/staging/usbip/usbip_common.o
  CC [M]  drivers/staging/usbip/usbip_event.o
  CC [M]  drivers/staging/usbip/stub_dev.o
  CC [M]  drivers/staging/usbip/stub_main.o
  CC [M]  drivers/staging/usbip/stub_rx.o
  CC [M]  drivers/staging/usbip/stub_tx.o
  CC [M]  drivers/staging/usbip/vhci_sysfs.o
  CC [M]  drivers/staging/usbip/vhci_tx.o
  CC [M]  drivers/staging/usbip/vhci_rx.o
  CC [M]  drivers/staging/usbip/vhci_hcd.o
  LD [M]  drivers/staging/usbip/usbip-core.o
  LD [M]  drivers/staging/usbip/vhci-hcd.o
  LD [M]  drivers/staging/usbip/usbip-host.o
  Building modules, stage 2.
  MODPOST 3 modules
  CC      drivers/staging/usbip/usbip-core.mod.o
  LD [M]  drivers/staging/usbip/usbip-core.ko
  CC      drivers/staging/usbip/usbip-host.mod.o
  LD [M]  drivers/staging/usbip/usbip-host.ko
  CC      drivers/staging/usbip/vhci-hcd.mod.o
  LD [M]  drivers/staging/usbip/vhci-hcd.ko

Mad!