From 65dad3bea6f039ff578e9f9bf04db929c2c42adb Mon Sep 17 00:00:00 2001
From: Tulio A M Mendes <tadryanom@hotmail.com>
Date: Wed, 11 Feb 2026 19:57:23 -0300
Subject: [PATCH] feat: per-process errno + set_thread_area syscall stub for
 future TLS

- user/errno.c: documented per-process errno isolation via fork
- include/syscall.h: added SYSCALL_SET_THREAD_AREA(57) for future TLS
- src/kernel/syscall.c: set_thread_area dispatch stub (-ENOSYS)
- True TLS deferred until clone/threads (task #14) is implemented
- cppcheck clean, 19/19 smoke tests pass
---
 include/syscall.h    | 2 ++
 src/kernel/syscall.c | 6 ++++++
 user/errno.c         | 3 +++
 3 files changed, 11 insertions(+)

diff --git a/include/syscall.h b/include/syscall.h
index c7cc012..2948163 100644
--- a/include/syscall.h
+++ b/include/syscall.h
@@ -76,6 +76,8 @@ enum {
     SYSCALL_LINK     = 54,
     SYSCALL_SYMLINK  = 55,
     SYSCALL_READLINK = 56,
+
+    SYSCALL_SET_THREAD_AREA = 57,
 };
 
 #endif
diff --git a/src/kernel/syscall.c b/src/kernel/syscall.c
index 0e0489a..999115e 100644
--- a/src/kernel/syscall.c
+++ b/src/kernel/syscall.c
@@ -2148,6 +2148,12 @@ void syscall_handler(struct registers* regs) {
         return;
     }
 
+    if (syscall_no == SYSCALL_SET_THREAD_AREA) {
+        /* Stub: will be implemented when clone/threads are added */
+        regs->eax = (uint32_t)-ENOSYS;
+        return;
+    }
+
     regs->eax = (uint32_t)-ENOSYS;
 }
 
diff --git a/user/errno.c b/user/errno.c
index 8330a8f..fbc6e36 100644
--- a/user/errno.c
+++ b/user/errno.c
@@ -1 +1,4 @@
+/* Per-process errno: each fork()ed process gets its own copy in its
+   address space.  When true threads (clone) are added, this must become
+   __thread int errno or use a TLS segment (GS/FS). */
 int errno = 0;
-- 
2.43.0