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(ld.info)PROVIDE

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PROVIDE
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   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, ANSI C requires that the user be able to use `etext' as a
function name without encountering an error.  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 = .);
         }
     }

   In this example, if the program defines `_etext' (with a leading
underscore), the linker will give a multiple definition error.  If, on
the other hand, the program defines `etext' (with no leading
underscore), the linker will silently use the definition in the program.
If the program references `etext' but does not define it, the linker
will use the definition in the linker script.