Failing to build; region `FLASH' overflowed by 680 bytes

[Will_20241202]

I am in process up migrating a legacy project from SDK v2.4 to v3.2 and going through each revision incrementally to catch all the changes needed to modernize it and maintain functionality.  I am able to build up to SDK v2.6.1 so far but stepping to v2.7.0 I am apparently running out of space, even though none of the configuration or source files have changed.  The target board uses an nrf52840 and what is especially peculiar is that the same code with the same proj.conf file and build configuration but targeting a board with an nrf52832 fits just fine, even though that chip has half the FLASH and a fraction of the RAM.  Clearly I'm missing a setting or something but honestly the Zephyr build environment is painfully opaque and unintuitive so I'm having trouble tracking it down.  For reference, the specific error I'm getting during build is:

[254/259] Linking C executable zephyr\zephyr_pre0.elf
FAILED: zephyr/zephyr_pre0.elf zephyr/zephyr_pre0.map C:/<REDACTED>/mcuboot/zephyr/zephyr_pre0.map
cmd.exe /C "cd . && C:\ncs\toolchains\ce3b5ff664\opt\zephyr-sdk\arm-zephyr-eabi\bin\arm-zephyr-eabi-gcc.exe  -gdwarf-4 zephyr/CMakeFiles/zephyr_pre0.dir/misc/empty_file.c.obj -o zephyr\zephyr_pre0.elf  zephyr/CMakeFiles/offsets.dir/./arch/arm/core/offsets/offsets.c.obj  -fuse-ld=bfd  -T  zephyr/linker_zephyr_pre0.cmd  -Wl,-Map=C:/<REDACTED>/mcuboot/zephyr/zephyr_pre0.map  -Wl,--whole-archive  app/libapp.a  zephyr/libzephyr.a  zephyr/arch/common/libarch__common.a  zephyr/arch/arch/arm/core/libarch__arm__core.a  zephyr/arch/arch/arm/core/cortex_m/libarch__arm__core__cortex_m.a  zephyr/arch/arch/arm/core/mpu/libarch__arm__core__mpu.a  zephyr/lib/libc/minimal/liblib__libc__minimal.a  zephyr/lib/libc/common/liblib__libc__common.a  zephyr/soc/soc/arm/nordic_nrf/lib..__modules__soc-hwmv1__soc__arm__nordic_nrf.a  zephyr/drivers/clock_control/libdrivers__clock_control.a  zephyr/drivers/flash/libdrivers__flash.a  zephyr/drivers/pinctrl/libdrivers__pinctrl.a  zephyr/drivers/timer/libdrivers__timer.a  modules/nrf/lib/fprotect/lib..__nrf__lib__fprotect.a  modules/nrf/drivers/hw_cc3xx/lib..__nrf__drivers__hw_cc3xx.a  modules/mcuboot/boot/bootutil/zephyr/libmcuboot_util.a  modules/mbedtls/libmbedTLSBase.a  modules/mbedtls/libmbedTLSCrypto.a  modules/mbedtls/libmbedTLSX509.a  modules/mbedtls/libmodules__mbedtls.a  modules/hal_nordic/nrfx/libmodules__hal_nordic__nrfx.a  -Wl,--no-whole-archive  zephyr/kernel/libkernel.a  -L"c:/ncs/toolchains/ce3b5ff664/opt/zephyr-sdk/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/12.2.0/thumb/v7e-m/nofp"  -LC:/<REDACTED>/mcuboot/zephyr  -lgcc  zephyr/arch/common/libisr_tables.a  modules/mbedtls/libmbedTLSBase.a  modules/mbedtls/libmbedTLSCrypto.a  modules/mbedtls/libmbedTLSX509.a  -mcpu=cortex-m4  -mthumb  -mabi=aapcs  -mfp16-format=ieee  -Wl,--gc-sections  -Wl,--build-id=none  -Wl,--sort-common=descending  -Wl,--sort-section=alignment  -Wl,-u,_OffsetAbsSyms  -Wl,-u,_ConfigAbsSyms  -nostdlib  -static  -Wl,-X  -Wl,-N  -Wl,--orphan-handling=warn  -Wl,-no-pie  C:/ncs/v2.7.0/nrfxlib/crypto/nrf_cc310_platform/lib/cortex-m4/soft-float/no-interrupts/libnrf_cc310_platform_0.9.19.a
&& cmd.exe /C "cd /D C:\<REDACTED>\mcuboot\zephyr && C:\ncs\toolchains\ce3b5ff664\opt\bin\cmake.exe -E true""c:/ncs/toolchains/ce3b5ff664/opt/zephyr-sdk/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/12.2.0/../../../../arm-zephyr-eabi/bin/ld.bfd.exe: zephyr\zephyr_pre0.elf section `rodata' will not fit in region `FLASH'
c:/ncs/toolchains/ce3b5ff664/opt/zephyr-sdk/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/12.2.0/../../../../arm-zephyr-eabi/bin/ld.bfd.exe: region `FLASH' overflowed by 680 bytes
collect2.exe: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

[Will_20241202]

I tried removing giant swathes of code from my project (both functions and static variables) and it still says I am exactly 680 bytes too big...  Which leads me to believe the problem lies outside of my code, and likely in the bootloader.  Is there an easy way to check how big the bootloader is and how big the container that it is being put into is?

[Amanda Hsieh]

You can check the CONFIG_PM_PARTITION_SIZE_MCUBOOT value in the .config file under build/mcuboot/zephyr and try to increase it. 

[Amanda Hsieh]

Try to build with "-Dmcuboot_CONF_FILE=prj_minimal.conf" to see if it helps. 

[Will_20241202]

Ok, couple new data points:

• If I change my build configuration Extra CMake arguments to "-Dmcuboot_CONF_FILE=prj_minimal.conf" it builds without overflowing
• Changing to "-Dmcuboot_CONF_FILE=C:/ncs/v2.7.0/bootloader/mcuboot/boot/zephyr/prj_minimal.conf" also builds within permitted size
• Editing the prj.conf file in the local mcuboot subdirectoy to mimic the above and using that builds  within size
• Experimenting with adding back in the original contents of the local prj.conf, the only line that seems to cause issues (meaning it no longer links within the permitted size) is the removal of "CONFIG_BOOT_USE_MIN_PARTITION_SIZE=y"

I cannot find any documentation from Google searching on what exactly this directive does or why I would want it set to either yes or no.

[Amanda Hsieh]

See https://github.com/nrfconnect/sdk-nrf/blob/v2.7.0/modules/mcuboot/boot/zephyr/Kconfig#L10-L25 

[Will_20241202]

Ok, but what does that mean?  Why wouldn't it always "Build for a minimal image size"?  What specifically changes if that option is not yes or is omitted altogether?

[Amanda Hsieh]

It will set the mcuboot partition to 0x7c00 for the mini size. The default size is 0xc000 if you don't use a static partition or CONFIG_PM_PARTITION_SIZE_MCUBOOT.