Re: [avr-libc-dev] PROGMEM section variables throw away by --gc-sections?

[Rolf Ebert]

Dean schrieb:
> Hi guys,
>
> I've been noticing some strange behaviour with my makefile arguments.
>
> Firstly, LD.exe crashes when I use -mshort-calls with the --relax linker 
> option, but *only* if I *don't* use -ffunction-sections and --gc-sections. With 
> the latter two options enabled both -mshort-calls and --relax work just fine.
>
> Secondly, -ffunction-sections and --gc-sections seems to throw away some of my 
> PROGMEM variables. I rely on a few PROGMEM variables being embedded into the 
> binary so I can later distinguish which version it was compiled from, similar 
> to:
>
> char PROGMEM buildtime[] = __TIME__;
>
> --gc-sections seems to remove this, although I thought it was only designed to 
> remove unused functions and not PROGMEM data. Is there a workaround to this?

--gc_sections removes all sections, that the linker thinks are unused. 
Did you compile also with the -fdata-sections compiler switch?

The assembler symbol of buildtime is not modified by 
-ffunction-sections, only by -fdata-sections.

I can also imagine a missing KEEP instruction in the linker script

Rolf