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Must I link against libc?

henry10210

Hello, I am working on a bare metal C++ ELF project targeting Zynq CPU1 (the 2nd CPU).  I successfully tested a simple Xilinx standalone application, and then started removing dependence on the standalone BSP, like this:
* I removed the BSP include and library paths from the project.
* I rewrote the startup.s and asm_vectors.s to not depend on any code from BSP.

But g++ linker is apparently still pulling in libc, as you can see below.  I will NOT use any libc functions.  Is there a way to tell g++ not to link against libc at all?  Thank you for your help!

arm-xilinx-eabi-g++ -L"/mnt/work/Dorking/QP/qpcpp/ports/arm/qk/zynq_rproc/Debug" -Wl,-T -Wl,../src/lscript.ld -o "cpu1app.elf"  ./src/bsp.o ./src/main.o ./src/philo.o ./src/table.o   -lqk
/mnt/opt/Xilinx/SDK/2014.4/gnu/arm/lin/bin/../lib/gcc/arm-xilinx-eabi/4.8.3/../../../../arm-xilinx-eabi/lib/libc.a(lib_a-abort.o): In function `abort':
abort.c:(.text+0x10): undefined reference to `_exit'
...

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    Certain low-level functions (like _exit) are required to be present and are part of the C-runtime provided by libc.  You may not be directly calling any of the functions contained in this object library from your application, but the fact that your compilation is complaining that certain functions are not present proves that there is indeed some low-level code that is attempting to access libc APIs.   You can of course write/include your own versions of the required run-time functions, but you may find there are more than you might think.

    Ron

  • 0 in reply to Former Member

    Thank you Ron, I am trying to figure out where in my code I am calling out to anything in libc.  Normally, a linker should print what function is calling out the undefined function, but the output you see doesn't.  Makes debugging difficult...

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