Building and debugging a monolithic bin/hex/elf/out

[Eliot Stock]

It would be useful in debugging to be able to fire up gdb and point it at a single binary so that I can step through code in both the bootloader and the application. The mergehex tool from Nordic makes it easy to merge soft device, bootloader and application hex files into one. I can then flash a single hex file. This much I can do now.

But I don't debug with the hex file - I debug with the elf file. And there's no such tool as "merge elf" that I can find. I guess I could start building both bootloader and application as a single project. We have no elf file for the soft device, only a hex file, but that should be OK to leave out of the combined elf file.

How can I build a combined elf file for both bootloader and application, ideally leaving them as separate projects in my build system? I'm using gcc and make.

Note that merging the hex files then going back to ELF from there appears not to be a good option, because the debug symbols are lost:

$make gdb-client
printf "target remote localhost:2331\nload\nmon reset\nbreak main\nset print elements 0\neval \"monitor exec SetRTTAddr %%p\", &_SEGGER_RTT\n" > _build/.gdbinit
/Users/Eliot/dev/gcc-arm-none-eabi-4_9-2015q3/bin/arm-none-eabi-gdb -x _build/.gdbinit _build/biketracker.elf
...
Reading symbols from _build/biketracker.elf...(no debugging symbols found)...done.
0x000006d0 in ?? ()
Loading section .sec1, size 0x7c0 lma 0x0
Loading section .sec2, size 0xf000 lma 0x1000
Loading section .sec3, size 0xafe0 lma 0x10000
Loading section .sec4, size 0x5000 lma 0x1b000
Loading section .sec5, size 0x10000 lma 0x20000
Loading section .sec6, size 0x6690 lma 0x30000
Loading section .sec7, size 0x7c24 lma 0x38000
Loading section .sec8, size 0x4 lma 0x10001014
Start address 0x0, load size 252504
Transfer rate: 41097 KB/sec, 3945 bytes/write.
Resetting target
No symbol table is loaded.  Use the "file" command.
Make breakpoint pending on future shared library load? (y or [n]) [answered N; input not from terminal]
_build/.gdbinit:6: Error in sourced command file:
No symbol table is loaded.  Use the "file" command.

[Thomas Stenersen]

Hi,

First of all make sure you build your project (and bootloader) with -g for adding the debug symbols to the .elf file. Next, take a look at the gdb command add-symbol-file https://sourceware.org/gdb/current/onlinedocs/gdb/Files.html#index-add_002dsymbol_002dfile-1172.

[Eliot Stock]

Yep, done that. Actually, I just realised the Makefile for the bootloader from the SDK does NOT build an .elf file at all yet. Just .bin, .out and .hex. And the .out file it builds is not debuggable, even in the _debug build. First of all, how do I modify Makefile.common to link an .elf file? Here's how it links the .out file:

# Link object files
%.out:
	@echo Linking target: $@
	$(NO_ECHO)$(CC) -Wl,-Map=$(@:.out=.map) $(LDFLAGS) $^ $(LIB_FILES) -lm -o $@
	-@echo ''
	$(NO_ECHO)$(SIZE) $@
	-@echo ''

[Vidar Berg]

Shouldn't be a problem to use .out instead of .elf, we use it for all of our GCC examples. However, you may want to disable link time optimization (remove -flto flag in Makefile). I my experience it does not always work well with debugging (maybe dependent on toolchain version).

[Eliot Stock]

OK, I'll stick to the .out file, forget the .elf file, run gdb against the application .out file and then use add-symbol-file to add the bootloader .out file. Will leave -flto out of my application build, but I see you've got it turned on for the armgcc debug build of the bootloader in SDK 12.1.0 btw.