Linker Script and Assigning a value to a specific address

Sadly I have no idea what those "invalid character" error messages are! Did you #include <icons.h> in your LD script before preprocessing it?
I would expect the " .abs_tristor50x35 ADDR50X35 : { *(ARM_AT_ADDR(ADDR50X35)) }" line to now feature the 0x0006A4CA after preprocessing

Sadly I have no idea what those "invalid character" error messages are! Did you #include <icons.h> in your LD script before preprocessing it?
I would expect the " .abs_tristor50x35 ADDR50X35 : { *(ARM_AT_ADDR(ADDR50X35)) }" line to now feature the 0x0006A4CA after preprocessing

First of all, when preprocessing as lscript.ld, it gives an error because #include "icons.h" cannot be found. So I changed the extension of the ldscript.ld file to ldscript.c. Likewise, there is the #include section at the beginning and under it are the linker script settings. The command I just ran is

arm-none-eabi-gcc -P -E ldscript.c > ldscript.ld

However, after this command, I received an invalid character error. this is because a problem with encoding. To solve this, I changed the command like this

arm-none-eabi-gcc -P -E  ldscript.c | % {$_ -replace "`r`n","`n"} | Out-File -Encoding ascii ldscript.ld 

and the problem was solved. However, I could not run it with #define's as you said. Instead, addresses are defined one by one in the ldscript.c file, and the preprocessing process must be repeated for each address change.

// ldscript.c file
#include "icons.h"
#define tristor50x35 0x65C00
MEMORY
{
  FLASH    (rx)  : ORIGIN = 0x00000000, LENGTH = 0x40000  /* 256 KB */
  FLASH_RW (rx)  : ORIGIN = 0x00040000, LENGTH = 0x40000  /* 256 KB */
  RAM      (rwx) : ORIGIN = 0x20000000, LENGTH = 0x18000  /*  96 KB */
}
SECTIONS
{
    //other parts
    .flash_rw :
    {
        //flash_rw section
    } > FLASH_RW
    .abs_tristor50x35 tristor50x35 : {*(.flash_rw.__at_tristor50x35)}
}

ld file created after preprocessing;

    .flash_rw :
    {
        . = ORIGIN(FLASH_RW);
        __flash_rw_start__ = .;
        *(.flash_rw)
        *(.flash_rw.*)
        . = ALIGN(4);
        __flash_rw_end__ = .;
    } > FLASH_RW
    .abs_tristor50x35 0x65C00 : { *(.flash_rw.__at_tristor50x35 ) }

Ok, interesting. There definitely must be something funky going on with your editor or operating system for the non-ascii characters to be creeping in. I suspect if you find out what that is and that all files start with the correct ASCII characters, then the on-the-fly replace and encoding change won't be needed.

Another tip:
"-x c " If you add that to your command line to the preprocessor it tells it to treat the input file as C code, regardless of the file extension. Then you won't need to go through renaming to ldscript.c.

What I was aiming for is a world where:

* icons.h contains the definitions for STRINGIFY, ARM_AT_ADDR, etc. and all the address definitions, e.g. "#define tristor50x35 0x65C00"

* your original ld script only #includes icons.h. It then uses the preprocessor macros in the SECTIONS command.

* your C code also only #includes icons.h and uses the preprocessor macros in the __attribute__(section)).

The benefit of this is that you end up defining the addresses in one place, rather than in multiple places. As such, you can more easily move things around in the memory map, and you have less of a maintenance burden when you want to change something