4.2.3. Importing linker-defined symbols
There are two ways to import linker-defined symbols into your C or C++ source code. Use either:
extern unsigned int symbol_name;
or:
extern void *symbol_name;
If you declare a symbol as an int, then you must use the address-of operator to obtain the correct value as shown in Example 4.2.
Example 4.2. Importing linker-defined symbols
extern unsigned int Image$$ZI$$Limit
config.heap_base = (unsigned int) &Image$$ZI$$Limit