From 2337a3b8864bdf4e700a9af020f665e9f4bec56d Mon Sep 17 00:00:00 2001
From: Gilles Peskine <Gilles.Peskine@arm.com>
Date: Fri, 22 Dec 2023 13:25:18 +0100
Subject: [PATCH] Explain the use of control

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
---
 scripts/common.make | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/scripts/common.make b/scripts/common.make
index a2d1449fea..6d2fbc3e2b 100644
--- a/scripts/common.make
+++ b/scripts/common.make
@@ -66,6 +66,10 @@ else # Not building for Windows
   SHARED_SUFFIX=
   ifndef THREADING
     # Auto-detect configurations with pthread.
+    # If the call to remove_unset_options returns "control", the symbols
+    # are confirmed set and we link with pthread.
+    # If the auto-detection fails, the result of the call is empty and
+    # we keep THREADING undefined.
     ifeq (control,$(call remove_unset_options,control MBEDTLS_THREADING_C MBEDTLS_THREADING_PTHREAD))
       THREADING := pthread
     endif