Why does getting the address of some linker variables stop the execution of SAMD21 in Rust with LLVM, but not in C with GCC?

Question

I am trying to get my Arduino MKRZero to work in Rust. I successfully blinked the LED, and my next step was to copy the global data from text to data.

I have the following linker variables:

Rust

extern {
    static __StackTop: u32;
    static mut __etext: u32;
    static mut __data_start__: u32;
    static mut __data_end__: u32;
    static mut __bss_start__: u32;
    static mut __bss_end__: u32;
} 

WITH

extern uint32_t __etext;
extern uint32_t __data_start__;
extern uint32_t __data_end__;
extern uint32_t __bss_start__;
extern uint32_t __bss_end__;
extern uint32_t __StackTop;

To shorten the long history, rust code

let mut pSrc: *mut u32;
pSrc = &mut __etext;

causes execution to stop, i.e. LED does not blink. Commenting out this line and moving on to the code that zeros the BSS segment

let mut pDest: *mut u32;
pDest = &mut __bss_start__;

makes blinker code work fine. As far as I can see, getting the address of the __etextlinker variable pauses execution, but getting the address __bss_start__is fine.

In version C there is no problem:

  uint32_t *pSrc, *pDest;
  pSrc = &__etext;
  pDest = &__data_start__;
  // <fill pDest with pSrc>

  for (pDest = &__bss_start__; pDest < &__bss_end__; pDest++)
  {
      *pDest = 0;
  }

( , ). arm-none-eabi-gcc Rust LLVM JSON, LLVM:

{
    "llvm-target"         : "thumbv6m-none-eabi",
    "data-layout"         : "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64",
    "linker"              : "arm-none-eabi-gcc",
    "pre-link-args"       : [ "-nostartfiles", "-Tlayout.ld" ],
    "target-endian"       : "little",
    "target-pointer-width": "32",
    "arch"                : "arm",
    "os"                  : "none",
    "executables"         : true
}

build.sh , , .

clang --target=thumbv6m-none-eabi -S -emit-llvm empty.c -o empty.ll

C , Rust . src/main.rs:38.

arm-none-eabi-objdump -Cd 1) C, 2) Rust 3) Rust . , , .

, LLVM C GCC, , - , C Rust C. MKRZero, , , - SAMD21 .