Hello all,
I maintain the AVR LLVM backend, for which downstream users typically use avr-gcc to link, so they get the CRT, startup routines, and libgcc.
I've noticed that AVR-GCC does not insert the __do_copy_data function for LLVM generated executables, but it does for GCC generated ones.
In case reads have not heard of this function, it is one of a few small routines which copies all variables from the .data, .rodata, and .bss in program memory into RAM during startup.
When does AVR-GCC insert __do_copy_data? How do I need to tune the output of LLVM in order to trigger GCC's insertion of this function?
I've looked at the GCC source and as far as I can tell, the logic is based in 'avr_asm_named_section' in 'gcc/config/avr/avr.c'. The code I can see just looks at the section names, sees if it can find sections prefixed with '.rodata', '.data', or '.bss'.
The LLVM backend is correctly placing my global variable into a section prefixed with '.data', but linking with avr-gcc still does not include __do_copy_data.
I have attached the output of 'objdump -t' for my reference LLVM and GCC program. They are not identical, but they both read from a global variable named 'FOO'.
blink.gcc.o.objdump