[chbot] AVR linker issue (?)

[Mark Atherton]

Thanks Andy, Richard.

Was hoping that I had just something daft.

Started looking at disassembly of the OBJ modules.

I don't plan to waste too much time on the problem. Failing all else, the parent module can subsume the table and the problem goes away; this will detract from modularity. Ho-hum.

Hope to see you all tomorrow eve at Robotics :)

-mark




> On 18 July 2021 at 10:14 Andrew Dachs <dachsa492 at gmail.com> wrote:
> 
> 
> A dependency issue maybe. Did it definitely recompile font.c? 
> Andy
> 
> Sent from my iPhone
> 
> > On 18/07/2021, at 9:02 AM, Mark Atherton <markaren1 at xtra.co.nz> wrote:
> > 
> > I need another pair of eyes to look at this issue as am obviously doing something daft. This is part of a larger problem; minimal code to show issue is below.
> > 
> > All I am trying to do is move a table into a separate module, but the linker is giving me a hard time.
> > 
> > Remove 'const' in the external module and everything works fine.
> > 
> > Thoughts please !
> > 
> > -Mark
> > 
> > 
> > -------------
> > 
> > mkdir -p .build
> > avr-g++ -c -g -Os -Wall -w -ffunction-sections -fdata-sections -mmcu=atmega328p -DF_CPU=16000000L font.c -o .build/font.o
> > avr-g++ -c -g -Os -Wall -w -ffunction-sections -fdata-sections -mmcu=atmega328p -DF_CPU=16000000L main.c -o .build/main.o
> > avr-gcc .build/font.o .build/main.o -o .build/hw.elf -Os -Wl,--gc-sections -mmcu=atmega328p -lm
> > 
> > .build/main.o: In function `main':
> > C:\Temp\linker_test/main.c:18: undefined reference to `ext_font'
> > collect2.exe: error: ld returned 1 exit status
> > make: *** [.build/hw.elf] Error 1
> > 
> > ------------- font.c
> > 
> > #include <avr\pgmspace.h>
> > 
> > const unsigned char ext_font[] =        // links OK with const removed
> > {
> >  0x00, 0x00, 0x00, 0x00, 0x00
> > };
> > 
> > ------------- font.h
> > 
> > #ifndef    _FONT_H_
> > #define _FONT_H_
> > 
> > extern const unsigned char ext_font[5]; // links OK with const removed
> > 
> > #endif
> > 
> > ------------- main.c
> > 
> > #include <avr\io.h>
> > #include <avr\pgmspace.h>
> > #include <ctype.h>
> > #include "font.h"
> > 
> > const unsigned char local_font[] = // const has no effect on linker !!
> > {
> >  0x00, 0x00, 0x00, 0x00, 0x00
> > };
> > 
> > int main(void)
> > {
> >  volatile unsigned char val;
> >  val = local_font[3];        // links OK
> >  val = ext_font[3];        // link Fails
> > 
> > }
> > 
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