How to specify global heap as box thread heap?

[ccli8]

In https://github.com/ARMmbed/uvisor/raw/docs/uvisor-rtos-docs.pdf, it mentions allocation fallback scheme:

“page-backed thread heap” -> “static process heap” -> “insecure global heap”

The sample https://github.com/ARMmbed/mbed-os-example-uvisor-thread gives how to specify page-backed thread heap or static process heap as box thread heap. But how to specify insecure global heap as box thread heap even though it is insecure?

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ARM Internal Ref: IOTSEC-246