when use arm-none-eabi-gcc compile the test c file, there is something wrong.some function couldn't found. Like follow that:
c:/program files (x86)/gnu tools arm embedded/4.9 2015q3/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib\libc.a(lib_a-exit.o): In function `exit':
exit.c:(.text.exit+0x2c): undefined reference to `_exit'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q3/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib\libc.a(lib_a-sbrkr.o): In function `_sbrk_r':
sbrkr.c:(.text._sbrk_r+0x18): undefined reference to `_sbrk'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q3/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib\libc.a(lib_a-writer.o): In function `_write_r':
writer.c:(.text._write_r+0x20): undefined reference to `_write'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q3/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib\libc.a(lib_a-closer.o): In function `_close_r':
closer.c:(.text._close_r+0x18): undefined reference to `_close'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q3/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib\libc.a(lib_a-fstatr.o): In function `_fstat_r':
fstatr.c:(.text._fstat_r+0x1c): undefined reference to `_fstat'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q3/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib\libc.a(lib_a-isattyr.o): In function `_isatty_r':
isattyr.c:(.text._isatty_r+0x18): undefined reference to `_isatty'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q3/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib\libc.a(lib_a-lseekr.o): In function `_lseek_r':
lseekr.c:(.text._lseek_r+0x20): undefined reference to `_lseek'
c:/program files (x86)/gnu tools arm embedded/4.9 2015q3/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/lib\libc.a(lib_a-readr.o): In function `_read_r':
readr.c:(.text._read_r+0x20): undefined reference to `_read'
collect2.exe: error: ld returned 1 exit status
could you help me