Add custom `unmapself` function as glue code

`unmapself()` provides a detached thread the ability
to free the memory region allocated for the stack and
TLS. In the original version, this function does
`munmap()', which will deallocate the thread's stack,
after which it executes exit() (NB: SYS_exit). This
works because there is another stack in the Kernel.
Since this does not exist in Unikraft, we implement
our version of unmapself.

Signed-off-by: Dragos Iulian Argint <dragosargint21@gmail.com>
Reviewed-by: Florin Postolache <florin.postolache80@gmail.com>
Reviewed-by: Simon Kuenzer <simon@unikraft.io>
Reviewed-by: Cezar Craciunoiu <cezar.craciunoiu@unikraft.io>
Reviewed-by: Razvan Deaconescu <razvand@unikraft.io>
Reviewed-by: Robert Kuban <robert.kuban@opensynergy.com>
Approved-by: Simon Kuenzer <simon@unikraft.io>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #9

diff --git a/__uk_unmapself.c b/__uk_unmapself.c
new file mode 100644 (file)
index 0000000..54a16d1
--- /dev/null
+++ b/__uk_unmapself.c
@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * Authors: Dragos Iulian Argint <dragosargint21@gmail.com>
+ *
+ * Copyright (c) 2022, University POLITEHNICA of Bucharest. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the copyright holder nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/types.h>
+#include <uk/print.h>
+#include <uk/alloc.h>
+#include <uk/sched.h>
+
+/*
+ * This glue code source is meant to replace the `__unmapself()`
+ * call in musl. When a thread is detached it must clear its mapped
+ * regions (e.g. stack). This is not a problem when running on Linux,
+ * because there is a stack in the kernel. For Unikraft we use a
+ * single stack. `__unmapself()' is an architecture-dependent function,
+ * but there is also a generic version in `src/thread/__unmapself.c'
+ * that uses a shared stack on which the code is run. However, we also
+ * have our version in which we deal with this special case in our own
+ * way. `__uk_unmapself()' will call a special version of `exit()'
+ * exposed by the sched library through which we can register a callback.
+ * This callback will be executed by another thread and will call `unmap()`.
+ */
+
+
+struct __map_area {
+       void *map_base;
+       size_t map_size;
+};
+
+int __munmap(void *map, size_t size);
+
+/*
+ * This will be called in the context of the `idle` thread
+ */
+static void __uk_unmapself_cb(struct uk_thread *t, void *mapped_area)
+{
+       uk_pr_debug("unmapself's callback is called\n");
+       struct __map_area *m = (struct __map_area *) mapped_area;
+
+       __munmap(m->map_base, m->map_size);
+}
+
+static __uk_tls struct __map_area __per_thread_map_area = {};
+
+void __uk_unmapself(void *base, size_t size)
+{
+       /*
+        * In order not to allocate memory (e.g. with malloc()) that could fail,
+        * we will use a variable in TLS to store the map address and size.
+        * When the callback will be run from the context of the `idle` thread,
+        * the TLS of this thread will be accessed, after which everything
+        * will be deallocated.
+        */
+       __per_thread_map_area.map_base = base;
+       __per_thread_map_area.map_size = size;
+
+       uk_sched_thread_exit2(__uk_unmapself_cb, &__per_thread_map_area);
+}