proc_rwmem help

Kernel development, writing drivers, coding, and questions regarding FreeBSD internals.

proc_rwmem help

Postby fernape » 07 Apr 2010, 18:25

Hi all,

I'm trying to read process memory other than the current process in kernel. I was told to use the proc_rwmem function, however I can't get it working properly. At first, I'm trying to read how many elements the environment variables vector has. To do this I tried this:

Code: Select all
   char *buff;
   struct iovec iov;
   struct uio tmp_uio;
   struct ps_strings *pss;
   int ret_code;

   buff = malloc(sizeof(struct ps_strings), M_TEMP, M_WAITOK);
   memset(buff, 0, sizeof(struct ps_strings));

   iov.iov_base = (caddr_t) buff;
   iov.iov_len = sizeof(struct ps_strings);
   tmp_uio.uio_iov = &iov;
   tmp_uio.uio_iovcnt = 1;
   tmp_uio.uio_offset = (off_t)(p->p_sysent->sv_psstrings);
   tmp_uio.uio_resid = sizeof(struct ps_strings);
   tmp_uio.uio_segflg = UIO_USERSPACE;
   tmp_uio.uio_rw = UIO_READ;
   tmp_uio.uio_td = td;
   ret_code = proc_rwmem(td->td_proc, &tmp_uio);

   if (ret_code == 0) {
      sbuf_printf(sb, "proc_rwmem successfully executed: %d\n", ret_code);
   } else {
      sbuf_printf(sb, "Error in proc_rwmem: %d\n", ret_code);

   pss = (struct ps_strings *)(iov.iov_base);
   sbuf_printf(sb, "ps_nargvstr = %d\nps_nenvstr = %d\n",
         pss->ps_nargvstr, pss->ps_nenvstr);

   free(buff, M_TEMP);

proc_rwmem returns 0 indicating no failure, but when I try to print the result, I get random stuff. I thought maybe the problem is in the uio_offset field, but p->p_sysent->sv_psstrings is a vm_offset_t. Is the offset properly specified? If not, what else could be the problem?

Thanks in advance.
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Posts: 2
Joined: 14 Feb 2010, 21:48

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