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### 12.2 Reentrant covers for OS subroutines

Since the system subroutines are used by other library routines that require reentrancy, `libc.a` provides cover routines (for example, the reentrant version of `fork` is `_fork_r`). These cover routines are consistent with the other reentrant subroutines in this library, and achieve reentrancy by using a reserved global data block (see Reentrancy).