[Pal/Linux-SGX] Rename enclave_tls to pal_tcb_sgx

[dimakuv]

• TLS stands for "Thread Local Storage" and is a memory area dedicated to storing app-specific thread-local variables.

• TCB stands for "Thread Control Block" and contains thread-specific internal state such as thread ID, stack pointer, and saved registers.

The Linux PAL correctly defines the struct pal_tcb. The Linux-SGX PAL however defines the struct enclave_tls. The enclave_tls name is misleading and breaks uniformity of code (see e.g. #555).

I suggest to rename:

• struct enclave_tls to struct pal_tcb_sgx
• SET/GET_ENCLAVE_TLS to SET/GET_ENCLAVE_TCB
• sgx_tls.h to sgx_tcb.h

If agreed, this change should be enacted after #555 is merged.

[yamahata]

+1 for naming consistency.

[mkow]

+1, though I also don't like "TCB", as it's used in SGX nomenclature as "Trusted Code Base". But we probably won't find any better name.

[HW42]

I also always read "trusted code base" first. But the suggested change seems reasonable.

[HW42]

SGX calls it internal thread specific state TCS ("Thread Control Structure"). So something like GTCS (Graphene TCS, to avoid confusion with the SGX's TCS) would be an options. But this naming might be too SGX specific.

[dimakuv]

@HW42: TCS is too SGX-specific. I still prefer TCB.