[chbot] AVR linker issue (?)

[Richard Jones]

Could the problem be to do with c++ compiler and c linker?
Sorry I don't have a windows machine to look further.

Richard Jones

On Sun, Jul 18, 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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