From 96023c2a8c240bd00c68b9a9e88c5989b2c80db1 Mon Sep 17 00:00:00 2001
From: Raoul Strackx <raoul.strackx@fortanix.com>
Date: Mon, 5 Sep 2022 13:34:04 +0200
Subject: [PATCH] Document `TCS` struct limitations

---
 intel-sgx/fortanix-sgx-abi/src/lib.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/intel-sgx/fortanix-sgx-abi/src/lib.rs b/intel-sgx/fortanix-sgx-abi/src/lib.rs
index 3511ae34..17188e6c 100644
--- a/intel-sgx/fortanix-sgx-abi/src/lib.rs
+++ b/intel-sgx/fortanix-sgx-abi/src/lib.rs
@@ -441,6 +441,9 @@ impl Usercalls {
 }
 
 /// The absolute address of a TCS in the current enclave.
+///
+/// To ensure a TCS struct will never be located at address 0, a TCS struct should not be located
+/// at the beginning of an enclave.
 // FIXME: `u8` should be some `extern type` instead.
 #[cfg_attr(feature = "rustc-dep-of-std", unstable(feature = "sgx_platform", issue = "56975"))]
 pub type Tcs = NonNull<u8>;