unresolvable symbol 'name' referenced in expression

Question

I have a function defined in a .c file (say funcs.c ):

void *funName()
{
    //implementation
}

and compiled to a library ( libname.so ).

And I'm compiling another .c file ( main.c ) which uses this function, and I'm setting symbol names in command line:

gcc -Wl,--just-symbols=symbolsfile.txt main.c -o main -lname

symbolsfile.txt :

FunSym = funName;
Symbol2 = expression2;
...

but I'm getting this linking error:

symbolsfile.txt:1: unresolvable symbol 'funName' referenced in expression
symbolsfile.txt:2: unresolvable symbol 'expression2' referenced in expression
collect2.exe: error: ld returned 1 exit status

I tried adding a function declaration in funcs.c (I don't have a corresponding .h file), but it didn't change a thing.

If I change FunSym = funName to FunSym = garbage , the error changes to " undefined symbol...", so I guess the expression funName is found.

Update:

I tried adding extern void *funName(); at the top of main.c or in a separate header file as suggested in the comments, but it didn't resolve the problem (same error). Is the flag --just-symbols needed to be added in compiling main.c or in compiling/linking the library ( libname.so )?

Answer 1

Move the flag --just-symbols from compiling main.c to linking the library. So compile the library like this:

gcc -g -Wl,--just-symbols=symbolsfile.txt -shared -o libname.so *.o

and main.c like this:

gcc main.c -o main -lname