From bc57635a82b91937317d89bde21700431b20f862 Mon Sep 17 00:00:00 2001
From: Julia Vassiliki <julia.vassiliki@unsw.edu.au>
Date: Fri, 13 Feb 2026 11:00:12 +1100
Subject: [PATCH] use LibSel4UseThreadLocals to disable TLS ipcbuf

See the motivation in the commit
    libsel4: make thread-local ipc buffer optional
in seL4 which adds this option.

Signed-off-by: Julia Vassiliki <julia.vassiliki@unsw.edu.au>
---
 build_sdk.py                   |  7 +++++++
 libmicrokit/include/microkit.h |  1 -
 libmicrokit/src/dbg.c          |  1 -
 libmicrokit/src/main.c         |  1 -
 monitor/src/main.c             | 21 ---------------------
 5 files changed, 7 insertions(+), 24 deletions(-)

diff --git a/build_sdk.py b/build_sdk.py
index 346932f86..3b560e7dc 100644
--- a/build_sdk.py
+++ b/build_sdk.py
@@ -45,6 +45,13 @@
 DEFAULT_KERNEL_OPTIONS = {
     "KernelIsMCS": True,
     "KernelRootCNodeSizeBits": "17",
+    # Thread local storage is painful and annoying to configure.
+    # We'd really rather NOT use thread local storage (especially
+    # consider we never have more than one thread in a Vspace)
+    #
+    # Turning off this feature removes the __thread attribute on
+    # __sel4_ipc_buffer and makes it a true global.
+    "LibSel4UseThreadLocals": False,
 }
 
 DEFAULT_KERNEL_OPTIONS_AARCH64 = {
diff --git a/libmicrokit/include/microkit.h b/libmicrokit/include/microkit.h
index db43ff99a..90155d21e 100644
--- a/libmicrokit/include/microkit.h
+++ b/libmicrokit/include/microkit.h
@@ -9,7 +9,6 @@
 
 #pragma once
 
-#define __thread
 #include <sel4/sel4.h>
 
 typedef unsigned int microkit_channel;
diff --git a/libmicrokit/src/dbg.c b/libmicrokit/src/dbg.c
index 298b3c12c..60090e42b 100644
--- a/libmicrokit/src/dbg.c
+++ b/libmicrokit/src/dbg.c
@@ -5,7 +5,6 @@
  */
 #include <microkit.h>
 
-#define __thread
 #include <sel4/sel4.h>
 
 void microkit_dbg_putc(int c)
diff --git a/libmicrokit/src/main.c b/libmicrokit/src/main.c
index c533bb0c5..cff14f642 100644
--- a/libmicrokit/src/main.c
+++ b/libmicrokit/src/main.c
@@ -7,7 +7,6 @@
 #include <stddef.h>
 #include <stdint.h>
 
-#define __thread
 #include <sel4/sel4.h>
 
 #include <microkit.h>
diff --git a/monitor/src/main.c b/monitor/src/main.c
index b2ff8019a..2adb47a5f 100644
--- a/monitor/src/main.c
+++ b/monitor/src/main.c
@@ -12,27 +12,6 @@
  *   Acting as the fault handler for protection domains.
  */
 
-/*
- * Why this you may ask? Well, the seL4 headers depend on
- * a global `__sel4_ipc_buffer` which is a pointer to the
- * thread's IPC buffer. Which is reasonable enough, passing
- * that explicitly to every function would be annoying.
- *
- * The seL4 headers make this global a thread-local global,
- * which is also reasonable, considering it applies to a
- * specific thread! But, for our purposes we don't have threads!
- *
- * Thread local storage is painful and annoying to configure.
- * We'd really rather NOT use thread local storage (especially
- * consider we never have more than one thread in a Vspace)
- *
- * So, by defining __thread to be empty it means the variable
- * becomes a true global rather than thread local storage
- * variable, which means, we don't need to waste a bunch
- * of effort and complexity on thread local storage implementation.
- */
-#define __thread
-
 #include <stdbool.h>
 #include <stdint.h>
 #include <sel4/sel4.h>