2.11.8. __user_stack_cleanup_space()
If defined, this function enables a SIGSTAK handler
to run after a stack overflow. It returns the size of the extra
stack your system requires.
__value_in_regs struct __stack_cleanup_space
_user_stack_cleanup_space(unsigned ignore);
There is no default implementation of this function.
If you define this function, it must return to r0 the
amount (measured in bytes) of extra stack that must be available
after stack overflow in order to support recovery from overflow.
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