ccache never "hits" on buildworld or buildkernel

[Maxim Khitrov]

Hello,

I'm using ccache to build FreeBSD source and ports. Ports work great,
I build something once and the second time just about everything is
found in the cache. For buildworld and buildkernel, however,
everything is a miss. Even when not a single thing changed about the
configuration or the actual source files.

Below is my make.conf configuration for ccache. Ccache is being used
via world-cc and world-c++ binaries for these two operations; I can
see the miss counter go up in 'ccache -s'. Why is it unable to
properly cache when building the source?

Thanks.

make.conf:

.if (!empty(.CURDIR:M/usr/src*) || !empty(.CURDIR:M/usr/obj*)) && \
    !defined(NOCCACHE) && exists(/usr/local/libexec/ccache)
CC= /usr/local/libexec/ccache/world-cc
CXX=/usr/local/libexec/ccache/world-c++
.endif

.if !empty(.CURDIR:M/usr/ports*) && !defined(NOCCACHE) \
    && exists(/usr/local/libexec/ccache)
CC= /usr/local/libexec/ccache/cc
CXX=/usr/local/libexec/ccache/c++
.endif

uname -a:

FreeBSD -.-.- 7.0-CURRENT FreeBSD 7.0-CURRENT #0: Sun Aug 12 15:45:05
EDT 2007     max at -.-.-:/usr/obj/usr/src/sys/KERNEL  i386