[GitHub] [incubator-nuttx] sebastianene07 commented on a change in pull request #1703: arch/sim: Add support for ucontext API

[GitBox <gi...@apache.org>]

sebastianene07 commented on a change in pull request #1703:
URL: https://github.com/apache/incubator-nuttx/pull/1703#discussion_r519154289



##########
File path: arch/sim/src/sim/up_ucontext.c
##########
@@ -0,0 +1,283 @@
+/****************************************************************************
+ * arch/sim/src/sim/up_ucontext.c
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+/* This define is required to compile on OSX */
+
+#ifndef _XOPEN_SOURCE
+#  define _XOPEN_SOURCE           (500)
+#endif
+
+#include <assert.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+#include <ucontext.h>
+
+/****************************************************************************
+ * Preprocessor Definition
+ ****************************************************************************/
+
+/* The minimum ucontext stack size */
+
+#define MIN_UCONTEXT_STACK_LENGTH (128 * 1024)
+#define STACK_ALIGNMENT_BYTES     (8)
+#define ASSERT(x)                 assert((x))
+#define ARRAY_LENGTH(array)       (sizeof((array))/sizeof((array)[0]))
+
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+
+/* This container stores the exit information for a NuttX task */
+
+typedef struct exit_data_context_s
+{
+  ucontext_t *parent_ucontext;    /* We jump to this context after we release
+                                   * the resources for the task that wants to
+                                   * exit.
+                                   */
+  ucontext_t *current_ucontext;
+  void *ucontext_sp;
+  int cpu_index;
+} exit_data_context_t;
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+/* This context is used on the exit path for the initial task */
+
+static ucontext_t g_uctx_main;
+
+/* We use an alternate ucontext for the task exit point to tear down
+ * allocated resources. On the task exit we jump to this exit context
+ * and we free the stack memory used by ucontext.
+ */
+
+#ifdef CONFIG_SMP
+static exit_data_context_t g_task_exit_details[CONFIG_SMP_NCPUS];
+static ucontext_t g_task_exit_context[CONFIG_SMP_NCPUS];
+static uint8_t
+  g_task_exit_context_stack[CONFIG_SMP_NCPUS][MIN_UCONTEXT_STACK_LENGTH];
+#else
+static exit_data_context_t g_task_exit_details[1];
+static ucontext_t g_task_exit_context[1];
+static uint8_t g_task_exit_context_stack[1][MIN_UCONTEXT_STACK_LENGTH];
+#endif
+
+/****************************************************************************
+ * Public Prototype
+ ****************************************************************************/
+
+#ifdef CONFIG_SMP
+int up_cpu_index(void);
+#endif
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: task_exit_point
+ *
+ * Description:
+ *   This function is used to release the allocated stack memory for a task
+ *   on it's exit path.
+ *
+ * Assumptions:
+ *   This function does not return.
+ *
+ ****************************************************************************/
+
+static void task_exit_point(void)
+{
+  for (; ; )
+    {
+      int cpu_id = 0;
+
+#ifdef CONFIG_SMP
+      cpu_id = up_cpu_index();
+#endif
+      if (g_task_exit_details[cpu_id].ucontext_sp)
+        {
+          /* Free stack memory used by the ucontext structure */
+
+          free(g_task_exit_details[cpu_id].current_ucontext);
+          free(g_task_exit_details[cpu_id].ucontext_sp);
+
+          /* Activate the parent ucontext */
+
+          setcontext(g_task_exit_details[cpu_id].parent_ucontext);
+        }
+    }
+}
+
+/****************************************************************************
+ * Name: up_setup_exit_context
+ *
+ * Description:
+ *   Creates new exit context for tasks. In a SMP configuration every CPU
+ *   has a different exit context.
+ *
+ ****************************************************************************/
+
+static void up_setup_exit_context(int cpu)
+{
+  ucontext_t *exit_context = &g_task_exit_context[cpu];
+  int ret = getcontext(exit_context);
+  ASSERT(ret >= 0);
+
+  uint8_t *sp = &g_task_exit_context_stack[cpu][0];
+
+  uint64_t align_offset = STACK_ALIGNMENT_BYTES - ((uint64_t)sp %
+      STACK_ALIGNMENT_BYTES);
+
+  uint8_t *aligned_stack = sp + align_offset;
+  exit_context->uc_stack.ss_sp   = aligned_stack;
+  exit_context->uc_stack.ss_size = MIN_UCONTEXT_STACK_LENGTH -
+    align_offset;
+  exit_context->uc_link          = &g_uctx_main;
+
+  makecontext(exit_context, task_exit_point, 0);
+}
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: up_create_context
+ *
+ * Description:
+ *   Creates a new ucontext structure and initialize it.
+ *
+ * Input Parameters:
+ *   ucontext_sp   - buffer where we store the ucontext stack pointer
+ *   prev_ucontext - the parent ucontext used%i to return to when the
+ *    execution of the current context ends.
+ *   entry_point   - the entry point of the new context
+ *
+ * Return Value:
+ *   A pointer to the ucontext structure or NULL in case something went
+ *   wrong.
+ *
+ ****************************************************************************/
+
+void *up_create_context(void **ucontext_sp, void *prev_ucontext,
+    void (*entry_point)(void))
+{
+  ucontext_t *new_context = calloc(1, sizeof(ucontext_t));
+  ASSERT(new_context != NULL);
+
+  int ret = getcontext(new_context);
+  ASSERT(ret >= 0);
+
+  uint8_t *sp = calloc(1, MIN_UCONTEXT_STACK_LENGTH);

Review comment:
       Hello @acassis thanks for your interest ! Unfortunately I hit some problems on the road with this patch because it doesn't seem to work well with SMP. I'm still investigating this.




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