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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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  • 0

    You can generate a linker map which will give you more information about locations and calling functions, and that may be sufficient.  Under the Build Settings, look for the Miscellaneous settings under the linker entries and add:

    -Wl,-Map=<yourMapFile.txt>

    If that is still not enough, what you might do is to include the necessary libraries to allow the project to link, but build the libraries with debug information included.  Then run the application in the debugger, which will give you the full call tree and let you see exactly where the offending calls are being made from.

    Ron

  • 0 in reply to e14 Contributor

    Thank you Ron, I agree with your suggestions.  I found that the linker has to be TOLD not to pull in the standard libs, and I had to resort to the techniques in this article: www.embedded.com/design/mcus-processors-and-socs/4007119/Building-Bare-Metal-ARM-Systems-with-GNU-Part-1--Getting-Started

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