libinterfork/interfork.c

   1 /* Copyright (C) 2009  Pierre-Marc Fournier
   2  *
   3  * This library is free software; you can redistribute it and/or
   4  * modify it under the terms of the GNU Lesser General Public
   5  * License as published by the Free Software Foundation; either
   6  * version 2.1 of the License, or (at your option) any later version.
   7  *
   8  * This library is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * Lesser General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU Lesser General Public
  14  * License along with this library; if not, write to the Free Software
  15  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
  16  */
  17
  18 #define _GNU_SOURCE
  19 #include <dlfcn.h>
  20 #include <unistd.h>
  21 #include <stdio.h>
  22 #include <signal.h>
  23 #include <ust/ust.h>
  24 #include <sched.h>
  25 #include <stdarg.h>
  26 #include <ust/tracectl.h>
  27 #include "usterr.h"
  28
  29 struct user_desc;
  30
  31 pid_t fork(void)
  32 {
  33         static pid_t (*plibc_func)(void) = NULL;
  34         ust_fork_info_t fork_info;
  35
  36         pid_t retval;
  37
  38         if(plibc_func == NULL) {
  39                 plibc_func = dlsym(RTLD_NEXT, "fork");
  40                 if(plibc_func == NULL) {
  41                         fprintf(stderr, "libcwrap: unable to find fork\n");
  42                         return -1;
  43                 }
  44         }
  45
  46         ust_before_fork(&fork_info);
  47
  48         /* Do the real fork */
  49         retval = plibc_func();
  50
  51         if(retval == 0) {
  52                 /* child */
  53                 ust_after_fork_child(&fork_info);
  54         }
  55         else {
  56                 ust_after_fork_parent(&fork_info);
  57         }
  58
  59         return retval;
  60 }
  61
  62 int execve(const char *filename, char *const argv[], char *const envp[])
  63 {
  64         static int (*plibc_func)(const char *filename, char *const argv[], char *const envp[]) = NULL;
  65
  66         pid_t retval;
  67
  68         if(plibc_func == NULL) {
  69                 plibc_func = dlsym(RTLD_NEXT, "execve");
  70                 if(plibc_func == NULL) {
  71                         fprintf(stderr, "libinterfork: unable to find execve\n");
  72                         return -1;
  73                 }
  74         }
  75
  76         ust_potential_exec();
  77
  78         retval = plibc_func(filename, argv, envp);
  79
  80         return retval;
  81 }
  82
  83 struct interfork_clone_info {
  84         int (*fn)(void *);
  85         void *arg;
  86         ust_fork_info_t fork_info;
  87 };
  88
  89 static int clone_fn(void *arg)
  90 {
  91         struct interfork_clone_info *info = (struct interfork_clone_info *)arg;
  92
  93         /* clone is now done and we are in child */
  94         ust_after_fork_child(&info->fork_info);
  95
  96         return info->fn(info->arg);
  97 }
  98
  99 int clone(int (*fn)(void *), void *child_stack, int flags, void *arg, ...)
 100 {
 101         static int (*plibc_func)(int (*fn)(void *), void *child_stack, int flags, void *arg, pid_t *ptid, struct user_desc *tls, pid_t *ctid) = NULL;
 102
 103         /* varargs */
 104         pid_t *ptid;
 105         struct user_desc *tls;
 106         pid_t *ctid;
 107
 108         int retval;
 109
 110         va_list ap;
 111
 112         va_start(ap, arg);
 113         ptid = va_arg(ap, pid_t *);
 114         tls = va_arg(ap, struct user_desc *);
 115         ctid = va_arg(ap, pid_t *);
 116         va_end(ap);
 117
 118         if(plibc_func == NULL) {
 119                 plibc_func = dlsym(RTLD_NEXT, "clone");
 120                 if(plibc_func == NULL) {
 121                         fprintf(stderr, "libinterfork: unable to find clone\n");
 122                         return -1;
 123                 }
 124         }
 125
 126         if(flags & CLONE_VM) {
 127                 /* creating a thread, no need to intervene, just pass on the arguments */
 128                 retval = plibc_func(fn, child_stack, flags, arg, ptid, tls, ctid);
 129         }
 130         else {
 131                 /* creating a real process, we need to intervene */
 132                 struct interfork_clone_info info = { fn: fn, arg: arg };
 133
 134                 ust_before_fork(&info.fork_info);
 135
 136                 retval = plibc_func(clone_fn, child_stack, flags, &info, ptid, tls, ctid);
 137
 138                 /* The child doesn't get here */
 139                 ust_after_fork_parent(&info.fork_info);
 140         }
 141
 142         return retval;
 143 }