How to debug a signed Zephyr application with MCUboot: ELF file missing header data

[ofirshe]

When I build my Zephyr application with CONFIG_BOOTLOADER_MCUBOOT=y and enable image signing, the zephyr.signed.bin contains valid data, but the zephyr.elf has zeros in the first 0x400 bytes (__rom_start_address). When I load the zephyr.elf via a debugger (Segger J-Link in Eclipse), this causes MCUboot to reject the image as invalid.

I want to debug from the very start (not just after main()), so I need the debugger to load the signed image, including the correct header. Is there a way to generate an ELF that matches zephyr.signed.bin so the debugger uploads the real data instead of zeros?

Thanks for help.

[nordicjm]

I'm a bit confused as to why you have asked this here after asking this exact question on discord and getting an answer that imgtool does not support elf file processing, hence no it is not supported. You flash the signed hex file then in a debugger attach to the running target with the elf file

[nordicjm]

But that's exactly how, you load MCUboot and the signed image ala west flash then you attach the elf which has the debug symbols and is built to be loaded by MCUboot ala west attach in the application build subdirectory (if using sysbuild). You would need to adapt your IDE to do that or similar, the above works and as a maintainer of multiple zephyr based bootloaders is something I use on a daily basis

[ofirshe]

Hey @nordicjm, you're right — attaching does work. However, it doesn't fully address the need to debug the entire application from the very beginning. If I want to debug something very early in the Zephyr OS (in my application, not MCUboot), I have to insert a long sleep just to give me time to attach the debugger — which isn't a convenient workflow.

If there were an ELF file corresponding to zephyr.signed.bin (which includes the valid data in the first 0x400 bytes), I could simply load that ELF in the IDE, reset the MCU, and debug from any point — just like I do when flashing only my application without a bootloader.

If this isn't currently supported, is there any way you could suggest to create such a zephyr.signed.elf file?

[nordicjm]

west flash --no-reset then the device will not reboot. There is no signed elf and no plans to support such an output

[ofirshe]

Alright, I’ll try to solve it on my own. But just for my understanding — what exactly is the data stored in the first 0x400 bytes of zephyr.signed.bin in the __rom_start_address section? Is it some kind of checksum or metadata related to the application?

[nordicjm]

https://docs.mcuboot.com/design.html#image-format