[GitHub] [incubator-nuttx] xiaoxiang781216 commented on a diff in pull request #6120: Implement execle, execve, execvp, execlp and execvpe

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

xiaoxiang781216 commented on code in PR #6120:
URL: https://github.com/apache/incubator-nuttx/pull/6120#discussion_r855216794


##########
libs/libc/unistd/lib_execle.c:
##########
@@ -0,0 +1,211 @@
+/****************************************************************************
+ * libs/libc/unistd/lib_execle.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
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <stdarg.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include "libc.h"
+
+#ifdef CONFIG_LIBC_EXECFUNCS
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+/* This is an artificial limit to detect error conditions where an argv[]
+ * and envp[] list is not properly terminated.
+ */
+
+#define MAX_EXECL_ARGS 256
+#define MAX_EXECL_ENVS 256
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: execle
+ *
+ * Description:
+ *   The standard 'exec' family of functions will replace the current process
+ *   image with a new process image. The new image will be constructed from a
+ *   regular, executable file called the new process image file. There will
+ *   be no return from a successful exec, because the calling process image
+ *   is overlaid by the new process image.
+ *
+ *   Simplified 'execl()' and 'execv()' functions are provided by NuttX for
+ *   compatibility.  NuttX is a tiny embedded RTOS that does not support
+ *   processes and hence the concept of overlaying a tasks process image with
+ *   a new process image does not make any sense.  In NuttX, these functions
+ *   are wrapper functions that:
+ *
+ *     1. Call the non-standard binfmt function 'exec', and then
+ *     2. exit(0).
+ *
+ *   Note the inefficiency when 'exec[l|v]()' is called in the normal, two-
+ *   step process:  (1) first call vfork() to create a new thread, then (2)
+ *   call 'exec[l|v]()' to replace the new thread with a program from the
+ *   file system.  Since the new thread will be terminated by the
+ *   'exec[l|v]()' call, it really served no purpose other than to support
+ *   Unix compatility.
+ *
+ *   The non-standard binfmt function 'exec()' needs to have (1) a symbol
+ *   table that provides the list of symbols exported by the base code, and
+ *   (2) the number of symbols in that table.  This information is currently
+ *   provided to 'exec()' from 'exec[l|v]()' via NuttX configuration setting:
+ *
+ *     CONFIG_LIBC_EXECFUNCS         : Enable exec[l|v] support
+ *     CONFIG_EXECFUNCS_SYMTAB_ARRAY : Symbol table name used by exec[l|v]
+ *     CONFIG_EXECFUNCS_NSYMBOLS_VAR : Variable holding number of symbols in
+ *                                     the table
+ *
+ *   As a result of the above, the current implementations of 'execl()' and
+ *   'execv()' suffer from some incompatibilities that may or may not be
+ *   addressed in a future version of NuttX.  Other than just being an
+ *   inefficient use of MCU resource, the most serious of these is that
+ *   the exec'ed task will not have the same task ID as the vfork'ed
+ *   function.  So the parent function cannot know the ID of the exec'ed
+ *   task.
+ *
+ * Input Parameters:
+ *   path - The path to the program to be executed.  If CONFIG_LIBC_ENVPATH
+ *     is defined in the configuration, then this may be a relative path
+ *     from the current working directory.  Otherwise, path must be the
+ *     absolute path to the program.
+ *   ... - A list of the string arguments to be recevied by the
+ *     program.  Zero indicates the end of the list.
+ *
+ * Returned Value:
+ *   This function does not return on success.  On failure, it will return
+ *   -1 (ERROR) and will set the 'errno' value appropriately.
+ *
+ ****************************************************************************/
+
+int execle(FAR const char *path, FAR const char *arg0, ...)
+{
+  FAR char **argv = NULL;
+  FAR char **envp = NULL;
+  FAR char *arg = (FAR char *)arg0;
+  size_t nargs;
+  size_t nenvs;
+  va_list ap;
+  size_t i;
+  int ret;
+
+  /* Count the number of arguments and environment variables */
+
+  va_start(ap, arg0);
+  nargs = 0;
+
+  while (arg != NULL)
+    {
+      /* Yes.. increment the number of arguments.  Here is a sanity
+       * check to prevent running away with an unterminated argv[] list.
+       * MAX_EXECL_ARGS should be sufficiently large that this never
+       * happens in normal usage.
+       */
+
+      if (++nargs > MAX_EXECL_ARGS)
+        {
+          set_errno(E2BIG);
+          va_end(ap);
+          return ERROR;
+        }
+
+      arg = va_arg(ap, FAR char *);
+    }
+
+  arg = va_arg(ap, FAR char *);
+  nenvs = 0;

Review Comment:
   Yes, you are right, I misunderstand how execle layout envp.



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