Question

During my project’s linking process the linker fails with the following errors unless I make an explicit call in my code to one of of the stub functions (i.e. _sbrk):

c:/toolchains/yagarto/bin/../lib/gcc/arm-none-eabi/4.6.2/../../../../arm-none-eabi/lib\libg.a(lib_a-abort.o): In function `abort':
C:\msys\1.0\home\yagarto\newlib-build\arm-none-eabi\newlib\libc\stdlib/../../../../../newlib-1.19.0/newlib/libc/stdlib/abort.c:63: undefined reference to `_exit'
c:/toolchains/yagarto/bin/../lib/gcc/arm-none-eabi/4.6.2/../../../../arm-none-eabi/lib\libg.a(lib_a-signalr.o): In function `_kill_r':
C:\msys\1.0\home\yagarto\newlib-build\arm-none-eabi\newlib\libc\reent/../../../../../newlib-1.19.0/newlib/libc/reent/signalr.c:61: undefined reference to `_kill'
c:/toolchains/yagarto/bin/../lib/gcc/arm-none-eabi/4.6.2/../../../../arm-none-eabi/lib\libg.a(lib_a-signalr.o): In function `_getpid_r':
C:\msys\1.0\home\yagarto\newlib-build\arm-none-eabi\newlib\libc\reent/../../../../../newlib-1.19.0/newlib/libc/reent/signalr.c:96: undefined reference to `_getpid'
c:/toolchains/yagarto/bin/../lib/gcc/arm-none-eabi/4.6.2/../../../../arm-none-eabi/lib\libg.a(lib_a-sbrkr.o): In function `_sbrk_r':
C:\msys\1.0\home\yagarto\newlib-build\arm-none-eabi\newlib\libc\reent/../../../../../newlib-1.19.0/newlib/libc/reent/sbrkr.c:60: undefined reference to `_sbrk'
collect2: ld returned 1 exit status

I am aware that I need some stubs functions that newlibc requires and I have a “C” file that contains all of the ones mentioned above as missing and I am also positive that the file is being compiled and added to an archive file (*.a) that is later linked.

I am calling the linker using the following commands

arm-none-eabi-gcc -L -T linkerscript.ld -nostartfiles -Wl,-Map,$(TARGET).map -lc archive.a

My question is simple (I hope) How can I make sure that the linker links my stub functions into the elf file without having to make an explicit function call from one of my project files?

Answer 1

I think those errors you’re getting refer to the linker not being able to find the appropriate library. My first suspicion is in how you’re using your arguments, specifically your specification of archive directory (-L) and the archive.a file. I’m thinking it should go like this:

arm-none-eabi-gcc -L. -T linkerscript.ld -nostartfiles -Wl,-Map,$(TARGET).map -lc -larchive

where the changes I’d make are:

1. -L. means use the current directory to look for library files to link.
2. -lc specifies to use the archive file libc.a.
3. -larchive specifies to use the archive file libarchive.a.

For more info I’d suggest checking out theGNU GCC reference.