OS: fixed segfault.

os/extra/src/main.c

@@ -19,9 +19,20 @@
 #include "input.lex.h"
 #include "input.l.h"
 
+/*
+ * Buffer size of path concatenation.
+ */
 #define PATH_LENGTH 1024
 
+/*
+ * When the shell is attached to a terminal, this value is true. If the shell
+ * is attached to a pipe, this value is false.
+ */
 int is_interactive = 0;
+
+/*
+ * Toggle debug messages. Only useful dring the development.
+ */
 int is_debug_mode = 1;
 
 /*
@@ -49,7 +60,6 @@ inline int base10len(unsigned int n) {
         return len + 1;
 }
 
-
 /*
  * Display a debug message, when running in debug mode, in stderr.
  */
@@ -133,6 +143,9 @@ shell_args *shell_pop_args() {
     return args;
 }
 
+/*
+ * Execute the binary and its parsed arguments.
+ */
 void shell_exec(shell_args *args) {
     assert(args && args->arg);
     shell_debug("exec `%s'", args->arg);
@@ -177,10 +190,11 @@ void shell_exec_process(shell_args *args) {
     // Convert argument structure to list of strings. And add a NULL pointer as
     // a marker for the end of the list. The first string should point to the
     // binary being executed.
+    assert(argc >= 1);
     char **argv = malloc((argc+1) * sizeof(char *));
     argv[0] = bin;
     shell_args *cur = args + sizeof(shell_args *);
-    for( int a = 0; a < argc && cur; cur = args->next, a++)
+    for( int a = 1; a < argc && cur; cur = args->next, a++)
         argv[a] = strdup(cur->arg);
     argv[argc] = NULL;