[U-Boot] Problem compiling u-boot for microblaze, libpost.a not found

["Carlos Salvador Pérez Salgado" <carlosalvatore@gmail.com>]

first petalinux:
...petalinux-v0.40-rc4$ source ./settings.sh
PetaLinux environment set to '/media/disk/uClinux/petalinux-v0.40-rc4'
next uboot:
...u-boot-microblaze$ alias ubmake="make ARCH=microblaze 
CROSS_COMPILE=microblaze-uclinux- -j4"
...u-boot-microblaze$ ubmake O="../uboot_test/" distclean
rm -rf /media/disk/uClinux/uboot_test/*
...u-boot-microblaze$ ubmake O="../uboot_test/" microblaze-generic_config
Configuring for microblaze-generic board...
...u-boot-microblaze$ ubmake O="../uboot_test/" all
make[1]: Entering directory `/media/disk/uClinux/u-boot-microblaze/post'
(echo create /media/disk/uClinux/uboot_test/post/libpost.a; for lib in   ; \
      do echo addlib $lib; done; echo save) \
     | microblaze-uclinux-ar -M
*microblaze-uclinux-ar: Can't open output archive 
tmp-/media/disk/uClinux/uboot_test/post/libpost.a*
make[1]: *** [/media/disk/uClinux/uboot_test/post/libpost.a] Error 9
make[1]: Leaving directory `/media/disk/uClinux/u-boot-microblaze/post'
make: *** [/media/disk/uClinux/uboot_test/post/libpost.a] Error 2
make: *** Waiting for unfinished jobs....

I want to know how could I fix this. Thank you!