Acessing global symbols from main.c

[Bert Lange]

Hi folks!

I wish to access global symbols from my main:

void main( void)
{
    extern uint16_t l__GSINIT;
    printf( "gsinit: %04X\n", l__GSINIT);
}

But at linker stage I got an error:

sdldz80  -n  -mwx  -m1 -u  -b _CODE=0x200 -l stuff.lib -l printf.lib  -i build/stuff.ihx  build/crt0.rel build/stuff.rel

?ASlink-Warning-Undefined Global '_l__GSINIT' referenced by module 'main'

The compiler(?) will add an underscore, because in the map file I can find the symbol:

ASxxxx Linker V03.00/V05.40 + sdld,  page 1.
Hexadecimal  [32-Bits]

Area                                    Addr        Size        Decimal Bytes (Attributes)
--------------------------------        ----        ----        ------- ----- ------------
.  .ABS.                            00000000    00000000 =           0. bytes (ABS,CON)

      Value  Global                              Global Defined In Module
      -----  --------------------------------   ------------------------
     00000000  .__.ABS.                           
     00000000  l__BSEG                         
     00000000  l__BSS                          
 ...
     00000022  l__GSINIT                       
 ...  

How can I make this work?

regards,
Bert

[Benedikt Freisen]

The compiler prepending an underscore is the expected behavior.
That happens to prevent name clashes.
I believe that you can use inline assembly to copy the value of a global variable originating from assembly code to a variable originating from C code, provided that you use the name of the latter with a prepended underscore within the inline assembly code block.

[Bert Lange]

Ok, thanks Benedikt. This will do:

uint16_t val; // need to be global (or use static and find the internal name)

void main( void)
{
    __asm
        ld hl, #(l__GSINIT)
        ld (_val), hl
    __endasm;
    printf( "l_gsinit: %04X\n", val);
}

regards,
Bert