Section `text` will not fit after upgrading `arm-none-eabi-gcc`

Question

I have an open source micromouse robot project. For easier compilation, I use containers (both Podman and Docker should be fine):

make image
make libopencm3
make

This works just fine and generates a main.elf file about 874 kB in size. But that is as long as I fix the arm-none-eabi-gcc-cs to 7.4.0 in the Dockerfile.

If I remove the specific version or set it to 9.2.0, then I get the following error:

$ make
/usr/lib/gcc/arm-none-eabi/9.2.0/../../../../arm-none-eabi/bin/ld: main.elf section `.text' will not fit in region `rom'
/usr/lib/gcc/arm-none-eabi/9.2.0/../../../../arm-none-eabi/bin/ld: region `rom' overflowed by 5288 bytes
collect2: error: ld returned 1 exit status
make: *** [opencm3/libopencm3.rules.mk:204: main.elf] Error 1

What could have changed between those versions?

If I add this line to my Makefile:

LDFLAGS         += -specs=nano.specs

Then it compiles just fine with version 9.2.0 and generates a main.elf file about 885 kB in size. But I wonder if the performance would be the same (or equivalent) as before.

Update

I am expecting some performance differences, of course, just like I was expecting some differences in the binary size. But I was wondering if I could expect a higher than 20% difference in performance (specially if it could be now 20% slower).

The new binary is less than 2% bigger, and I would consider this to be "the same" as before. :-D

Answer 1

I do perfectly understand you want to use the latest and greatest toolchain from your prefered, mainstream Linux distribution, but this is not always going well.

In my humble opinion, you should:

• stick to Linaro or ARM gcc toolchains,
• in the case of your specific cortex-m related project, stick to a gcc toolchain more specifically targeting the cortex-m, i.e. the so called 'GNU Arm Embedded Toolchain'.

Some remarks:

• There are probably excellent reasons why ARM itself is providing two specifics toolchains for the two profiles,
• Latest GCC toolchain version available from Linaro is 7.4.1, but if they used to point to it by default on this page, they now pointing to version 7.2.1, which may (or not) ring a bell regarding 7.4.1 - there are no official 9.2 versions available yet.
• Latest GCC toolchain available from ARM is 8.3.1 for cortex-m, and 8.3 for cortex-a - there are no official 9.2 versions available yet.

Back to your specific issue now: I was able to compile your project using the following steps:

wget "https://developer.arm.com/-/media/Files/downloads/gnu-rm/8-2019q3/RC1.1/gcc-arm-none-eabi-8-2019-q3-update-linux.tar.bz2?revision=c34d758a-be0c-476e-a2de-af8c6e16a8a2?product=GNU%20Arm%20Embedded%20Toolchain,64-bit,,Linux,8-2019-q3-update" -O gcc-arm-none-eabi-8-2019-q3-update-linux.tar.bz2
mkdir -p /opt/arm
tar jxf gcc-arm-none-eabi-8-2019-q3-update-linux.tar.bz2 -C /opt/arm
export PATH=/opt/arm/gcc-arm-none-eabi-8-2019-q3-update/bin:$PATH

Command which arm-none-eabi-gcc should display /opt/arm/gcc-arm-none-eabi-8-2019-q3-update/bin/arm-none-eabi-gcc.

git clone --recurse-submodules https://github.com/Bulebots/bulebule.git
cd bulebule
scripts/setup_libopencm3.sh
make -s -C src/

Command arm-none-eabi-size ./src/main.elf should display:

text    data     bss     dec     hex filename
55152    3336    7100   65588   10034 ./src/main.elf

Please note that there is a Docker file for the latest GCC toolchain from ARM targeting the cortex-m profile here. You may want to use it in your own Docker file and remove those two lines:

arm-none-eabi-gcc-cs-7.4.0 \
arm-none-eabi-newlib-3.1.0-2.fc30 \

I hope this helps.