Re: static link problems with alias

[Nick Clifton <nickc at redhat dot com>]

Hi Carmelo,

> I've encountered a problem doing a static link due to duplicated symbols 
> error.

You appear to misunderstand how aliases and libraries work...

> I have the following dummy functions:
> - int foo();
> - foo_alias() as weak alias of foo()
> - int bar(); (thats call foo_alias())
> all archived into libfoo_alias.a

Note that in your libfoo_alias.a you have a *strong* definition of a 
symbol called "foo" and a *weak* definition of a symbol called "foo_alias".

> and the following ones:
>
> int foo();
> int other();
> archied into libfoo.a

Note that in libfoo.a you have a *second* strong definition of a symbol 
called "foo".

> and the main.c calling bar() and other().
>
> When I compile the main with the following command:
>
> gcc -static -L. main.c -lfoo_alias -lfoo I get the following error:
>
> ./libfoo.a(foo.o)(.text+0x0): In function `foo':
> : multiple definition of `foo'
> ./libfoo_alias.a(foo_alias.o)(.text+0x0): first defined here

Which is quite correct.  It goes like this:

  1) main calls bar.  bar is defined in libfoo_alias:bar.o

  2) bar calls foo_alias.  foo_alias is weakly defined in 
libfoo_alias:foo.o, but there are no strong definitions provided 
elsewhere, so the weak definition is used.  Hence libfoo_alias:foo.o is 
included in the link which brings with it a strong definition of the 
"foo" symbol.

  3) main calls other.  other is defined in libfoo.a:foo.o. 
libfoo.a:foo.o also defines "foo", hence there is now a duplicate 
definition.

What you probably wanted was the following:

  1) Edit foo.c and add these lines to the end:

int foo_alias () {
  return 2;
}

  This provides a strong definition of the foo_alias symbol which can 
override the weak definition in foo_alias.c.

  2) Change the gcc link command line to:

gcc -static -L. main.c -lfoo -lfoo_alias

  ie moving the linking of libfoo.a to before libfoo_alias.a so that 
the strong definition of foo_alias is available when the reference to it 
is encountered in libfoo_alias:bar.o.

Cheers
  Nick