9.5.3.2 Provide Command

In some cases, it is desirable for a linker script to define a symbol only if it is referenced and is not defined by any object included in the link. For example, traditional linkers defined the symbol etext. However, the C standard indicates that etext is a valid function name. The PROVIDE keyword may be used to define a symbol, such as etext, only if it is referenced but not defined. The syntax is:

PROVIDE(symbol = expression)

.

Here is an example of using PROVIDE to define etext:

   SECTIONS
{
  .text :
   {
     *(.text)
     _etext = .;
     PROVIDE(etext = .);
   }
}

If the symbol etext is defined by the program, that definition is used by the linker. If it is not defined by the program, then the definition provided by the linker script is used. Compare this with the definition for _etext (with a leading underscore) in the linker script, which will trigger an error if it is also defined in the program.

The default linker script used with PIC32M devices makes use of the PROVIDE command to define the default _min_stack_size, _min_heap_size, and _vector_spacing symbol values, for example:

PROVIDE(_min_stack_size = 0x400) ;
PROVIDE(_min_heap_size = 0) ;
PROVIDE(_vector_spacing = 0x00000001);