C++ to ASM linkage in GCC: Difference between revisions

In assembly, (NASM, specifically; the author does not use GAS. Anyone who knows how GAS works may add to this article as they see fit.) all symbols are automatically local to the particular assembly file in which they appear. To make a symbol global, you must use the 'global _SYMBOL_NAME_' directive. If I remember right, in GAS, that's '.globl _SYMBOL_NAME'.

 

;-------------------------------------

; I usually like to place all my directives in a section above the code:

ret

 

 

To clarify, technically, the linker can 'see' all symbols. It just chooses to ignore linkage between files for symbols not exclusively declared global. If you were to write a second file:

 

;--------------------------------------

; Extern directives here

extern mylocalsymbol

;--------------------------------------

 

This file will assemble, but when passed through the linker, you will receive a message to the effect that no such symbol has been defined for 'mylocalsymbol'.

If you do the following:

 

class foo {

public:

extern foo fubar;

extern "C++" foo fubar

 

The compiler will take them both to mean the same thing: 'Link to an external symbol which has the ''demangled'' name fubar, and is of type foo'.