Re: MAXSTRINGLEN applied to printf()?

[halcyonic at gmail dot com]

Sorry...didn't want to spam a lot of code and output.

So, for example, I get a long output that contains this fragment:

... ,"localhost.localdomain"localhost.localdomain_2012-8-8-23-47-30.bz2", ...

...generated by the following probe (I've set string lengths to be 2048).  The thing to notice is that any string concatenation I do should always involve the addition of a pair of quotes, so I should never be able to get an output that involves an odd number of quotes (as per above).  So either I'm somehow getting intermingled output (I don't think I am...the rest of the output looks perfectly fine), or somehow a string is getting silently truncated somewhere (fyi, all the filenames it's listing are of the form localhost.localdomain_2012-8-8-23-47-30.bz2).

Any theories appreciated.

Thanks,
Nick

-----
probe syscall.getdents.return {
    if ((execname() != "stap") && !is_fd_blacklisted(pid(), $fd)) {
    printf("{ \"arglist\":")
    arglist = "[ "
    if ($return > 0) {
        total_entries = 0
        dirent = $dirent
        total_bytes = 0
        current_bytes = 0
        while (total_bytes < $return) {
          if (dirent == 0) {
              break
          }
          nextarg = clean_string(user_string_warn(@cast(dirent, "struct linux_dirent")->d_name))
          len = @cast(dirent, "struct linux_dirent")->d_reclen
          formatlen = strlen(nextarg) + 2
          dirent += len
          total_bytes += len
          total_entries += 1

          if (total_entries < 256) {
              if (current_bytes + formatlen > 2048) {
                printf("%s", arglist)
                arglist = ""
                current_bytes = 0
              }
              
              arglist .= "\"".nextarg."\""
              current_bytes += formatlen 
              if (total_bytes < $return) {
                arglist .= ","
              }
          }          
        }
    }
    printf("%s],", arglist)
#    arglist = substr(arglist, 0, strlen(arglist)-1)."]"
#    outstr = "{ "
#    outstr .= "\"arglist\": "
#    outstr .= arglist.","
    outstr .= "\"count\": "
    outstr .= sprintf("%u", $count).","
    outstr .= "\"execname\": \""
    outstr .= clean_string(execname())."\","
    outstr .= "\"fd\": "
    outstr .= sprintf("%d", $fd).","
    outstr .= "\"op\": \""
    outstr .= clean_string("GETDENTS")."\","
    outstr .= "\"pid\": "
    outstr .= sprintf("%d", pid()).","
    outstr .= "\"ppid\": "
    outstr .= sprintf("%d", ppid()).","
    outstr .= "\"return\": "
    outstr .= sprintf("%d", $return).","
    outstr .= "\"timestamp\": "
    outstr .= sprintf("%d", gettimeofday_ms()).","
    outstr .= "\"total_bytes\": "
    outstr .= sprintf("%u", total_bytes).","
    outstr .= "\"total_entries\": "
    outstr .= sprintf("%u", total_entries).","
    outstr .= "\"uid\": "
    outstr .= sprintf("%d", uid())."}\n"
    printf("%s", outstr)
  }
}
-----

On Aug 9, 2012, at 12:56 PM, Josh Stone <jistone@redhat.com> wrote:

> On 08/08/2012 09:01 PM, halcyonic@gmail.com wrote:
>> If I try to printf() more than MAXSTRINGLEN characters without
>> outputting a newline, does that mean I'm exceeding the string length
>> limit?  I.e., is just a normal string serving as the printf buffer,
>> and all the normal rules about strings apply to it?  (I was trying to
>> get around the string length limits by issuing multiple printf()'s,
>> but that seems to be backfiring...)
> 
> As long as you're not using intermediate strings, MAXSTRINGLEN should
> not limit you.  There is a different limit STP_BUFFER_SIZE which is 8192
> bytes, but I believe even that is for each individual printf call.
> 
> As before, examples of what you're trying and the result would be helpful.
> 
> 
> Josh