Jeff Johnson wrote:
On Jun 16, 2010, at 4:59 PM, Markdv wrote:
Jeff Johnson wrote:
I happen to have a valgrind trace on my screen that shows the issue
==25160== ==25160== 49 bytes in 1 blocks are still reachable in loss record 2
of 2
==25160== at 0x4005BDC: malloc (vg_replace_malloc.c:195)
==25160== by 0x314D9A: poptGetNextOpt (popt.c:1203)
==25160== by 0x40697CD: rpmcliInit (poptALL.c:751)
==25160== by 0x804AC45: main (rpmqv.c:385)
==25160== The "memory leak" is actually a POPT design feature. Every string
returned from POPT is malloc'd so that an application
can do whatever it wishes with the string without
worrying about side effects of fiddling with the memory.
Unfortunately, POPT is mostly not used correctly, and the expectation is
Hey POPT handles argv strings, I shouldn't _HAVE_ to manage those!?!
I don't mind having to manage those, as long as it is documented.
I just started using libpopt for the very first time today and checked my code with
valgrind which showed a leak. The minimal program below always leaks an amount of memory
equal to the length of the argument of the "hostname" option +1. Despite the
fact that I think I'm free-ing everything I'm supposed to free... After skimming the
libpopt source I inserted the two commented lines that, when uncommented (duh), seem to
fix the leak... lucky shot I guess. :)
Does this not demonstrate that there actually is a memory leak in popt?
I use popt & valgrind daily in all sorts of configurations.
So no, it does _NOT_ demonstrate that there's a leak in popt.
The whole point of my e-mail is/was that the arg is malloc'd by
intent so that the application can do whatever it wishes
with the returned memory.
Clear. And I think that the "leak" I demonstrated is not the same one
you are talking about. Sorry for confusing the issue.
And its not sufficient to document the behavior (which has been this
way for a decade). Inquiring minds want to know even if the
amount of memory is <100b.
Misunderstood you, thought you meant something else. Never mind.
If not, I would appreciate someone explaining how I'm using libpopt wrongly.
#include <stdio.h>
#include <stdlib.h>
#include <popt.h>
/** #include "/tmp/popt-1.14/poptint.h" **/
You should not ever need/want to include "poptint.h" which
contains routines and data structures internal to popt.
Well DUH!, I only did this in this case in order to be able to access
the structure member that I thought should have been freed. Just in
order to demonstrate the "problem".
struct opts {
char *hostname;
int verbose;
} opts;
struct poptOption optTable[] = {
{"hostname", 'h', POPT_ARG_STRING, &opts.hostname,
0, "hostname", "HOST" },
{"verbose", 'v', POPT_ARG_NONE, &opts.verbose,
0, "be verbose", 0 },
POPT_AUTOHELP
POPT_TABLEEND
};
int main( int argc, const char **argv )
{
poptContext optCon;
optCon = poptGetContext(NULL, argc, argv,
optTable, POPT_CONTEXT_POSIXMEHARDER);
Do you _REALLY_ want/need POSIXMEHARDER? The issue is
largely whether options must strictly proceed args or not.
Yes, perhaps, but beside the point imho.
IIRC (I don't use anything but popt for option processing)
getopt_long() default behavior in linux is _NOT_ POSIXly correct
but rather the more convenient process --foo where ever found.
poptGetNextOpt(optCon);
There's usually a loop over poptGetNextOpt. E.g. here's what is in RPM
Yes, but there doesn't have to be a loop. At least not according to the
documentation, from popt(3):
If all of the command-line options are handled through arg
pointers, command-line parsing is reduced to the following
line of code:
rc = poptGetNextOpt(poptcon);
Which is exactly what I'm doing...
/* Process all options, whine if unknown. */
while ((rc = poptGetNextOpt(optCon)) > 0) {
const char * optArg = poptGetOptArg(optCon);
optArg = _free(optArg);
switch (rc) {
default:
fprintf(stderr, _("%s: option table misconfigured (%d)\n"),
__progname, rc);
exit(EXIT_FAILURE);
/*...@notreached@*/ /*...@switchbreak@*/ break;
}
}
The free in the loop is what is needed for "squeaky clean".
What's the big difference? Instead of manually getting the optArg in the
loop I have them assigned to variables via "arg pointers". And I _do_
free that memory after I'm done with it.
So (afaict) I'm using libpopt in a documented way, and freeing
everything I can and am supposed to free, and still it "leaks".
But truly, I wouldn't fuss too much about 10-20 bytes of "leak".
glibc leaks far more than that, but the leaks are masked in valgrind.
I agree completely, aside from the fact that valgrind output does not
show the program as "squeaky clean" it's absolutely nothing to really
worry about. But having it show as clean instead of showing some
possible problem that I have to look at before realising "oh, no, that's
just the usual libpopt thingy" would be nice.
I just don't see why you wouldn't want to "fix" this. Seems like all
you'd have to do is add
con->os->nextArg = _free(con->os->nextArg);
to poptFreeContext(poptContext con) and be done with it.
And technically none of these are "leaks" because its one-time
allocation, not continually increasing unfree'd memory.
Also true, but I'd just like to be able to show-off the valgrind output
and go "Look ma! No leaks!!" and get the cookie without having to
explain anything.
printf("Options:\n"
"hostname: %s\n"
"verbose: %d\n",
opts.hostname,
opts.verbose);
free(opts.hostname);
/** free(optCon->os->nextArg); **/
poptFreeContext(optCon);
See if the loop fixes, then try using poptGetOptArg()
and free the result.
It does not. Because all my options use arg pointers poptGetNextOpt
parses everything on the first invocation after which it returns -1. So
the loop body never executes.
Whether that is obvious or convenient or correct or documented is a different
matter.
>
But whatever behavior is implemented in POPT has been largely unchanged this
century.
What? A bug - albeit not a very serious one - that's been there for ever
is, therefore, not a bug?
Regards,
Mark.
return 0;
}
Regards,
Mark.
I get a tedious bug report every couple of months from otherwise honest
attempts to use valgrind for application "squeaky clean" memory auditing.
Should this behavior be changed in POPT 2.0? It's a 1-liner change to remove
a strdup() somewhere, but the change does have profound (but minor, who
actually cares about a 49b 1-time memory leak these days) ramifications.
Meanwhile I'm way tired of explaining why its _NOT_ a memory leak, but rather
buggy use of POPT.
Opinions welcomed.
73 de Jeff
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