Some relocatable rust code

reloc.rs

/* Use this linker script:

```text
SECTIONS {
    . = 0x10000000;

    Flash : {
        KEEP(*(.entry))
        KEEP(*(.entry.*))

        *(.text)
        *(.text.*)

        *(.rodata)
        *(.rodata.*)

        . = ALIGN(4);
    }

    Ram : {
        *(.data)
        *(.data.*)

        *(.sdata)
        *(.sdata.*)
        
        *(.bss)
        *(.bss.*)

        *(.uninit)
        *(.uninit.*)

        . = ALIGN(4);
    }

    /DISCARD/ : {
        /* Unused exception related info that only wastes space */
        *(.ARM.exidx);
        *(.ARM.exidx.*);
        *(.ARM.extab.*);
    }
}
```

And build with this command:

rustc -o reloc -C opt-level=3 reloc.rs --crate-type=bin -C relocation-model=ropi-rwpi  --target=thumbv6m-none-eabi -C link-arg=-Tlink.x

*/

#![no_std]
#![no_main]

use core::sync::atomic;

static GLOBAL_VALUE: atomic::AtomicI32 = atomic::AtomicI32::new(5);

static GLOBAL_VALUE2: atomic::AtomicI32 = atomic::AtomicI32::new(0);

#[inline(never)]
#[no_mangle]
#[link_section = ".entry"]
pub fn reloc_get() -> i32 {
    GLOBAL_VALUE.load(atomic::Ordering::Relaxed) + GLOBAL_VALUE2.load(atomic::Ordering::Relaxed)
}

#[link_section = ".entry"]
#[no_mangle]
pub fn reloc_add(a: i32) -> i32 {
    let x = reloc_get();
    a.wrapping_add(x)
}

#[link_section = ".entry"]
#[no_mangle]
pub fn reloc_update(foo: i32) {
    GLOBAL_VALUE.store(foo, atomic::Ordering::Relaxed);
    GLOBAL_VALUE2.store(foo, atomic::Ordering::Relaxed);
}

#[panic_handler]
fn panic_handler(_info: &core::panic::PanicInfo) -> ! {
    loop {}
}