RFR [XS] : 8239224: libproc_impl.c previous_thr may be used uninitialized warning

[Baesken, Matthias]

Hi David,  building  with gcc / -Os  sometimes gives strange (+different) warnings  when comparing to the other O-modes.

> I don't see the need for the NULL check however as previous_thr can't be
> NULL if we reach that part of the code.

What about   current_thr != NULL,  but   current_thr == thr_to_be_removed   ?
The we would not enter the body of the while-loop ,   would not return early in 283  , but we would  access  "previous_thr->next = current_thr->next;"   ?


 277       while (current_thr && current_thr != thr_to_be_removed) {
 278         previous_thr = current_thr;
 279         current_thr = current_thr->next;
 280       }
 281       if (current_thr == NULL) {
 282         print_error("Could not find the thread to be removed");
 283         return;
 284       }
 285       if (previous_thr != NULL) {
 286         previous_thr->next = current_thr->next;
 287       }


Best regards, Matthias


> 
> On 17/02/2020 11:10 pm, Baesken, Matthias wrote:
> > Hello, please review this small fix.
> >
> > When building a product build  with gcc7 on linux x86_64, and trying out
> different optimization options, I run into this error when
> > optimizing for space (-Os)  :
> >
> >
> >
> /open_jdk/jdk_5/jdk/src/jdk.hotspot.agent/linux/native/libsaproc/libproc_i
> mpl.c: In function 'delete_thread_info':
> >
> /open_jdk/jdk_5/jdk/src/jdk.hotspot.agent/linux/native/libsaproc/libproc_i
> mpl.c:285:26: error: 'previous_thr' may be used uninitialized in this function [-
> Werror=maybe-uninitialized]
> >         previous_thr->next = current_thr->next;
> >         ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
> >
> > We should probably better initialize previous_thr to avoid this warning.
> >
> > (it does not show up however with the default optimization options ).
> 
> Seems like a spurious warning to me but initializing to NULL is harmless.
> 
> I don't see the need for the NULL check however as previous_thr can't be
> NULL if we reach that part of the code.
> 
> Thanks,
> David
> 
> >
> > Bug/webrev :
> >
> > https://bugs.openjdk.java.net/browse/JDK-8239224
> >
> > http://cr.openjdk.java.net/~mbaesken/webrevs/8239224.0/
> >
> >
> > Thanks, Matthias
> >