1. create asm listing: compile .o only, then use objdump kos32-tcc.exe -c -g clipview.c -o clipviewtcc.o kos32-objdump -d -M intel -S -l clipviewtcc.o > clipviewtcc.asm 2. see offset in resulting kolibri executable compared to listing (i have 0xD0) 3. in kolibri debugger mtdbg set breakpoint to funtion address >bp 140 where 0x140 is 0x70 in assemly + offset 0xD0 Warning !!Error. sometimes tcc dont warn about unsuccesful linking (not found function body code). Hopefully, i fix this. Usually, at runtime you have crash with "Illegal cpu instruction" In assembler code this is easy to recognize as myaddr:E8 FC FF FF FF call myaddr+1 4.how to see defines kos32-tcc.exe -E -dD null 5.if you use GNU LD as a linker, add option -Map=hellocpp.map to ld. Mtdbg can use resulting .map file 6.now you can use -g option to generate .dbg file. This enables source code level debugging with Mtdbg