Fix dlclose / exit running in parallel resulting in dtor being called twice
Commit Message
* Florian Weimer:
> * Paul Pluzhnikov:
>
>> On Wed, Feb 6, 2019 at 1:37 AM Florian Weimer <fweimer@redhat.com> wrote:
>>>
>>> * Paul Pluzhnikov:
>>>
>>> > + /* Clear any errors. */
>>> > + dlerror ();
>>> > + return dso;
>>> > +}
>>>
>>> Why did you add the dlerror call in the success case?
>>
>> I don't remember / can't recall.
>>
>> But it seems like it should always be a no-op. Do you have a case
>> where dlopen() succeeds and dlerror() is not a no-op?
>
> I think it may matter for dlsym, where you need to look dlerror to tell
> if the symbol was NULL, or there was an actual error. But you would
> have to clear dlerror *before* dlsym anyway, in case something else had
> called dlsym without clearing the error.
In other words, something like this.
Thanks,
Florian
support: Use dlerror to detect NULL symbols in xdlsym
2019-02-06 Florian Weimer <fweimer@redhat.com>
* support/xdlfcn.c (xdlopen, xdlclose): Do not call dlerror.
(xdlsym): Use dlerror to detect a NULL symbol.
Comments
On Wed, Feb 6, 2019 at 7:28 AM Florian Weimer <fweimer@redhat.com> wrote:
> > I think it may matter for dlsym, where you need to look dlerror to tell
> > if the symbol was NULL, or there was an actual error. But you would
> > have to clear dlerror *before* dlsym anyway, in case something else had
> > called dlsym without clearing the error.
>
> In other words, something like this.
The patch looks good to me.
Thanks!
@@ -28,22 +28,25 @@ xdlopen (const char *filename, int flags)
if (dso == NULL)
FAIL_EXIT1 ("error: dlopen: %s\n", dlerror ());
- /* Clear any errors. */
- dlerror ();
-
return dso;
}
void *
xdlsym (void *handle, const char *symbol)
{
+ /* Clear any pending errors. */
+ dlerror ();
+
void *sym = dlsym (handle, symbol);
if (sym == NULL)
- FAIL_EXIT1 ("error: dlsym: %s\n", dlerror ());
-
- /* Clear any errors. */
- dlerror ();
+ {
+ const char *error = dlerror ();
+ if (error != NULL)
+ FAIL_EXIT1 ("error: dlsym: %s\n", error);
+ /* If there was no error, we found a NULL symbol. Return the
+ NULL value in this case. */
+ }
return sym;
}
@@ -53,7 +56,4 @@ xdlclose (void *handle)
{
if (dlclose (handle) != 0)
FAIL_EXIT1 ("error: dlclose: %s\n", dlerror ());
-
- /* Clear any errors. */
- dlerror ();
}