Why does my linker script not include my subroutine in the target memory section when I declare (void) __attribute__ ((section (".rwdata"))) in the code?

The linker in the Nios® II IDE will not automatically put a subroutine in a memory that is not designated as .text.

In order to include the subroutine in a specific memory section other than .text (in this example, .rwdata), do the following:

1. Define a custom section for this specific routine, for example: void my_subroutine(void) __attribute__ ((section (".usersection")));
2. Open the generated.x file that is located in your <sw_proj>_syslib/Debug/system_description folder and look for the __ram_rwdata_end
3. Add the following lines to the generated.x file:

.usersection : AT ( LOADADDR (.rwdata) SIZEOF (.rwdata) )

{
      PROVIDE (_alt_partition_usersection_start = ABSOLUTE(.));
     *(.usersection .usersection.*)
     . = ALIGN(4);
     PROVIDE (_alt_partition_usersection_end = ABSOLUTE(.));

} >onchip_ram

        PROVIDE (__flash_alt_partition_usersection_start = LOADADDR(.usersection));

4. Modify alt_load.c to perform the custom section copy operation. See below for reference:

extern void __flash_alt_partition_usersection_start;
extern void _alt_partition_usersection_end;
extern void _alt_partition_usersection_start;

/*

* Copy the .usersection section.

*/     
      
  alt_load_section (&__flash_alt_partition_usersection_start,
                  &_alt_partition_usersection_start,
                  &_alt_partition_usersection_end);