arm64: fix stack pointer initialization when CONFIG_STACK_COLORATION …

[hujun260]

Summary

Fix ARM64 multi-core stack pointer initialization when CONFIG_STACK_COLORATION is not defined. The boot code now correctly advances the stack pointer (x24) by SMP_STACK_SIZE for each CPU even when stack coloration is disabled, preventing adjacent CPU stacks from overlapping. The fix adds a missing else clause to handle the non-coloration code path.

Changes

• arch/arm64/src/common/arm64_head.S:
  • Add else clause after CONFIG_STACK_COLORATION conditional in real_start label
  • In the non-coloration path, advance x24 (current stack pointer) by SMP_STACK_SIZE
  • Ensures proper per-CPU stack spacing regardless of CONFIG_STACK_COLORATION setting

Benefits & Technical Details

• Correct stack layout: Each CPU stack occupies SMP_STACK_SIZE bytes without overlap
• Configuration independence: Stack initialization works correctly with or without coloration enabled
• Boot safety: Prevents stack corruption from concurrent CPU initialization
• Multi-core correctness: Ensures each CPU has properly isolated stack space
• Consistency: Matches stack pointer advancement behavior from coloration code path

Testing

• Verified stack pointers correctly spaced by SMP_STACK_SIZE for each CPU without coloration
• Confirmed no stack corruption when multiple CPUs boot simultaneously without coloration enabled
• Tested system boot with CONFIG_STACK_COLORATION disabled on multi-core ARM64
• Validated stack traces show correct stack boundaries for each CPU
• Confirmed no memory overlap between different CPU stacks

Impact

• Correctness: Fixes multi-core stack initialization bug when coloration is disabled
• Compatibility: Fully backward compatible, no API changes
• Configuration: Particularly important for builds without CONFIG_STACK_COLORATION
• Scope: Affects ARM64 multi-core boot sequence and stack initialization