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README.md

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This is a minimal functioning program that will run on a Cortex-M0. It simply calls __libc_init_array() and then loops.

  1. Set xpack arm-none-eabi-gcc v11.3 to be first in your PATH.

    Run ./build.sh. Output is:

   text    data     bss     dec     hex filename
   4084       0     512    4596    11f4 build/test.elf

build/test.map reveals that lib_a-init.o references symbol __aebi_unwind_cpp_pr0, and thus the linker included unwind-arm.o. This then causes libunwind.o and pr-support.o to be included. This ends up being a little under 4kB of code added to the .text section.

  1. Uncomment this line in main.cc:
char __aeabi_unwind_cpp_pr0[0];

Run ./build.sh. Output:

   text    data     bss     dec     hex filename
    136       0     520     656     290 build/test.elf

We see the size has shrunk to a reasonable 136 bytes.

  1. Now use the official ARM gcc release v11.2. Doesn't matter if you keep the line defining __aeabi_unwind_cpp_pr0

    Run build.sh. Output is:

   text    data     bss     dec     hex filename
    120       0     512     632     278 build/test.elf

  1. Now use the official ARM gcc release v11.2 and change the build flags by removing -fno-unwind-tables -fno-exceptions.

    Run build.sh. Output is:

   text    data     bss     dec     hex filename
   4084       0     512    4596    11f4 build/test.elf

So the exception code is back, but only because we requested it by not specifying -fno-exceptions