anchao opened a new pull request, #21438:
URL: https://github.com/apache/nuttx/pull/21438
## Summary
When `realloc()` moves a block forward by consuming a preceding free
chunk (the `takeprev` path in `mm_realloc.c`), the destination starts
at a lower address than the source and the two user regions overlap.
The previous code used `memcpy()`, whose behavior is undefined for
overlapping regions. Depending on libc optimizations, architecture,
or compiler settings this could corrupt user data.
Switch to `memmove()`, which is guaranteed to handle overlapping
regions correctly.
## Impact
- **New behavior**: Overlapping downward copy in `realloc()` uses
`memmove()` instead of `memcpy()`.
- **User impact**: Fixes a potential data-corruption bug in the default
heap allocator path.
- **Build**: None (no new dependencies).
- **Documentation**: None.
- **Security**: None (bug fix; reduces undefined behavior).
## Testing
sim/nsh
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