stack_fill.s File Reference

Memory check utilities: stack filler. More...

Variables
syntax unified thumb global MemStackFill word _Stack_Fill_Value word _sheap word _estack section text MemStackFill type	MemStackFill
syntax unified thumb global MemStackFill word _Stack_Fill_Value word _sheap word _estack section text MemStackFill type function adds	r2
syntax unified thumb global MemStackFill word _Stack_Fill_Value word _sheap word _estack section text MemStackFill type function adds	LoopFillHeapStack

Detailed Description

Memory check utilities: stack filler.

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Author

SMFSW

Copyright

MIT (c) 2017-2026, SMFSW

Note

_Stack_Fill_Value has to be defined in linker script with 32b value to fill stack with (eg: _Stack_Fill_Value = 0xB00BFACE;)

MemStackFill has to be called by startup routine (after memory init steps, AND prior to any memory used on heap or stack), You may want to call stack fill routine:
1) for every build target, add:

bl MemStackFill 

2) only for specific targets:

PREFERED METHOD
     // Declare weak external symbol. If the linker finds a real definition elsewhere, it's used;
     // if not, the symbol resolves to 0 (NULL) instead of causing a link error.
     .weak MemStackFill
     // Load the (possibly 0) address of external symbolinto r0. This is resolved by the linker,
     // so it correctly reflects whether the symbol was ultimately defined anywhere in the final image.
     ldr r0, =MemStackFill
     // "Compare and Branch if Zero": if r0 == 0 (symbol was never defined, so it's NULL),
     // skip the call and jump to label 1.
     cbz r0, 1f
     // Otherwise, branch-and-link to the address in r0, i.e. call optional_cb().
     // "x" allows switching between ARM/Thumb state if needed.
     blx r0
   1: // Local label "1:" — landing point when there was nothing to call.
   // `cbz .. 1f` is GNU assembler's **local label** syntax, not a special instruction field.
   // **The rule:**
   // - A label like `1:` (just a digit) is a *local/numeric label* — you can reuse the number `1` many times in the same file for different spots.
   // - When you *reference* it, you must say which direction to search:
   //  - `1f` = search **f**orward from here for the next `1:` label.
   //  - `1b` = search **b**ackward from here for the nearest previous `1:` label.

 CORES WITHOUT CBZ INSTRUCTION SUPPORT
...
//Call memory stack filler (following build target)
  bl MemStackFill
...
 
// Create weak MemStackFill routine (in startup file)
  .section  .text.MemStackFill
  .weak  MemStackFill
  .type  MemStackFill, %function
// Fill the user heap & stack.
MemStackFill:
  bx lr
 
  .size  MemStackFill, .-MemStackFill

Variable Documentation

LoopFillHeapStack

syntax unified thumb global MemStackFill word _Stack_Fill_Value word _sheap word _estack section text MemStackFill type function adds LoopFillHeapStack

MemStackFill

syntax unified thumb global MemStackFill word _Stack_Fill_Value word _sheap word _estack section text MemStackFill type function adds r4 bcc FillHeapStack bx lr size MemStackFill

r2

syntax unified thumb global MemStackFill word _Stack_Fill_Value word _sheap word _estack section text MemStackFill type function adds r2