close is not implemented for bfin-elf?

I have just created a bare-metal program with the bfin-elf toolchain and when I compile it I get the following warnings:

/public/gnu/2011R1-RC1/bfin-elf/bin/../lib/gcc/bfin-elf/4.3.5/../../../../bfin-elf/lib/libc.a(lib_a-closer.o): In function `_close_r':

/usr/src/packages/BUILD/blackfin-toolchain-2011R1/gcc-4.3/newlib/libc/reent/closer.c:53: warning: _close is not implemented and will always fail
/public/gnu/2011R1-RC1/bfin-elf/bin/../lib/gcc/bfin-elf/4.3.5/../../../../bfin-elf/lib/libc.a(lib_a-fstatr.o): In function `_fstat_r':
/usr/src/packages/BUILD/blackfin-toolchain-2011R1/gcc-4.3/newlib/libc/reent/fstatr.c:62: warning: _fstat is not implemented and will always fail
/public/gnu/2011R1-RC1/bfin-elf/bin/../lib/gcc/bfin-elf/4.3.5/../../../../bfin-elf/lib/libc.a(lib_a-isattyr.o): In function `_isatty_r':
/usr/src/packages/BUILD/blackfin-toolchain-2011R1/gcc-4.3/newlib/libc/reent/isattyr.c:58: warning: _isatty is not implemented and will always fail
/public/gnu/2011R1-RC1/bfin-elf/bin/../lib/gcc/bfin-elf/4.3.5/../../../../bfin-elf/lib/libc.a(lib_a-lseekr.o): In function `_lseek_r':
/usr/src/packages/BUILD/blackfin-toolchain-2011R1/gcc-4.3/newlib/libc/reent/lseekr.c:58: warning: _lseek is not implemented and will always fail
/public/gnu/2011R1-RC1/bfin-elf/bin/../lib/gcc/bfin-elf/4.3.5/../../../../bfin-elf/lib/libc.a(lib_a-readr.o): In function `_read_r':
/usr/src/packages/BUILD/blackfin-toolchain-2011R1/gcc-4.3/newlib/libc/reent/readr.c:58: warning: _read is not implemented and will always fail
/public/gnu/2011R1-RC1/bfin-elf/bin/../lib/gcc/bfin-elf/4.3.5/../../../../bfin-elf/lib/libc.a(lib_a-writer.o): In function `_write_r':
/usr/src/packages/BUILD/blackfin-toolchain-2011R1/gcc-4.3/newlib/libc/reent/writer.c:58: warning: _write is not implemented and will always fail

Why are these occuring and how do I make them work?