Symbol binding directives

Description

Operation

The symbol binding directive can be at any point in the assembly file, before or after any references or definitions of the symbol.

If the binding of a symbol is not specified using one of these directives, the default binding is:

• If a symbol is not defined in the assembly file, it has global visibility by default.
• If a symbol is defined in the assembly file, it has local visibility by default.

Examples

    // This function has global binding, so can be referenced from other object
    // files. The symbol 'value' defaults to local binding, so other object
    // files can use the symbol name 'value' without interfering with this
    // definition and reference.
    .global get_val
  get_val:
    ldr r0, value
    bx lr
  value:
    .word 0x12345678

    // The symbol 'printf' is not defined in this file, so defaults to global
    // binding, so the linker searches other object files and libraries to
    // find a definition of it.
    bl printf

    // The debug_trace symbol is a weak reference. If a definition of it is
    // found by the linker, this call is relocated to point to it. If a
    // definition is not found (e.g. in a release build, which does not include
    // the debug code), the linker points the bl instruction at the next
    // instruction, so it has no effect.
    .weak debug_trace
    bl debug_trace