[L2Ork-dev] Segfault using paste from clipboard on Linux

[Jonathan Wilkes]

On Thu, Jun 18, 2020 at 4:29 PM Ivica Ico Bukvic <ico at vt.edu> wrote:
>
> It's by far the most SNAFU'd implementation of a for loop I've ever
> seen. So much so, I am not even sure what it exactly does:
>
>     -->     for (g = x->gl_list; g2 = g->g_next; g = g2)
>                      ;

This is all about that inane ", f $value" syntax that Miller wrote, didn't
test, and then got changed in a later Pd Vanilla version.

This bug is probably from Purr Data attempted to support this
deprecated ", f 12;"
syntax plus the fixed behavior that just uses "#X f 12;" on the next line.

I'd like to continue supporting both syntaxes, otherwise uses of the old syntax
will hit the bug and be sad.

See the note in line above `t_symbol *last_typedmess;` to understand
what's going
on.

I'll drill down on this later and see what's up.

And just to be clear-- I only attempted to do damage control around that
looper, I didn't write it. (Yet another reason why we should just be
using arrays,
but that's for another time.)

-Jonathan

>
> I am assuming it is looking for the last element in the gl_list. If so,
> I have no idea how this has worked so far, since I do not see any kind
> of a check whether g->g_next is not NULL... This is also the only place
> in the entire function (canvas_f) that uses t_gobj *g2.
>
> Running uner that assumption, I refactored it as:
>
> g = x->gl_list;
> if (g) // probably unnecessary but hey let's be pedantic
>      while (g->g_next)
>          g = g->g_next;
>
> Once this is implemented, the segfault now happens on line 2282
> (immediately below) on the first pd_checkobject(&g->g_pd) which also
> segfaults with an invalid read of size 8...
>
>
> On 6/18/2020 4:13 PM, Jonathan Wilkes wrote:
> > On Thu, Jun 18, 2020 at 3:32 PM Ivica Bukvic <ico at vt.edu> wrote:
> >> Valgrind is a bit more descriptive. It does not happen every time but it does happen nonetheless. Looks like Windows is a lot less forgiving. I was pasting the content of a simple patch multiple times (close the window, new window, paste again):
> >>
> >> #N canvas 487 261 450 300 10;
> >> #X floatatom 145 63 5 0 0 0 - - -, f 5;
> >> #X obj 241 123 print;
> >> #X floatatom 126 134 5 0 0 0 - - -, f 5;
> >> #X connect 0 0 1 0;
> >>
> >> ==12982== Invalid read of size 8
> >> ==12982==    at 0x436EF3: canvas_f (g_canvas.c:2273)
> > Something's off for me because 2273 isn't inside canvas_f().
> >
> > Can you tell me what's at that line number in whatever is your current branch?
> >
> > -Jonathan
> >
> >> ==12982==    by 0x49B977: pd_typedmess (m_class.c:779)
> >> ==12982==    by 0x49B7DD: pd_typedmess (m_class.c:883)
> >> ==12982==    by 0x4A4D80: binbuf_eval (m_binbuf.c:937)
> >> ==12982==    by 0x4AC56B: socketreceiver_read (s_inter.c:615)
> >> ==12982==    by 0x4AB554: sys_domicrosleep.constprop.3 (s_inter.c:226)
> >> ==12982==    by 0x4AE35A: sys_pollgui (s_inter.c:1155)
> >> ==12982==    by 0x4A84B9: m_pollingscheduler (m_sched.c:542)
> >> ==12982==    by 0x4A84B9: m_mainloop (m_sched.c:622)
> >> ==12982==    by 0x4AAEF9: sys_main (s_main.c:440)
> >> ==12982==    by 0x5ED882F: (below main) (libc-start.c:291)
> >> ==12982==  Address 0x8 is not stack'd, malloc'd or (recently) free'd
> >> ==12982==
> >> ==12982==
> >> ==12982== Process terminating with default action of signal 11 (SIGSEGV)
> >> ==12982==  Access not within mapped region at address 0x8
> >> ==12982==    at 0x436EF3: canvas_f (g_canvas.c:2273)
> >> ==12982==    by 0x49B977: pd_typedmess (m_class.c:779)
> >> ==12982==    by 0x49B7DD: pd_typedmess (m_class.c:883)
> >> ==12982==    by 0x4A4D80: binbuf_eval (m_binbuf.c:937)
> >> ==12982==    by 0x4AC56B: socketreceiver_read (s_inter.c:615)
> >> ==12982==    by 0x4AB554: sys_domicrosleep.constprop.3 (s_inter.c:226)
> >> ==12982==    by 0x4AE35A: sys_pollgui (s_inter.c:1155)
> >> ==12982==    by 0x4A84B9: m_pollingscheduler (m_sched.c:542)
> >> ==12982==    by 0x4A84B9: m_mainloop (m_sched.c:622)
> >> ==12982==    by 0x4AAEF9: sys_main (s_main.c:440)
> >> ==12982==    by 0x5ED882F: (below main) (libc-start.c:291)
> >> ==12982==  If you believe this happened as a result of a stack
> >> ==12982==  overflow in your program's main thread (unlikely but
> >> ==12982==  possible), you can try to increase the size of the
> >> ==12982==  main thread stack using the --main-stacksize= flag.
> >> ==12982==  The main thread stack size used in this run was 8388608.
> >> ==12982==
> >> ==12982== HEAP SUMMARY:
> >> ==12982==     in use at exit: 355,586 bytes in 3,885 blocks
> >> ==12982==   total heap usage: 7,748 allocs, 3,863 frees, 2,870,428 bytes allocated
> >> ==12982==
> >> ==12982== LEAK SUMMARY:
> >> ==12982==    definitely lost: 416 bytes in 9 blocks
> >> ==12982==    indirectly lost: 85 bytes in 10 blocks
> >> ==12982==      possibly lost: 43,438 bytes in 1,323 blocks
> >> ==12982==    still reachable: 311,647 bytes in 2,543 blocks
> >> ==12982==         suppressed: 0 bytes in 0 blocks
> >> ==12982== Rerun with --leak-check=full to see details of leaked memory
> >> ==12982==
> >> ==12982== For counts of detected and suppressed errors, rerun with: -v
> >> ==12982== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
> >>
> >> --
> >> Ivica Ico Bukvic, D.M.A.
> >> Director, Creativity + Innovation
> >> Institute for Creativity, Arts, and Technology
> >>
> >> Virginia Tech
> >> Creative Technologies in Music
> >> School of Performing Arts – 0141
> >> Blacksburg, VA 24061
> >> (540) 231-6139
> >> ico at vt.edu
> >>
> >> ci.icat.vt.edu
> >> www.icat.vt.edu
> >> www.performingarts.vt.edu
> >> l2ork.icat.vt.edu
> >> ico.bukvic.net
>
> --
> Ivica Ico Bukvic, D.M.A.
> Director, Creativity + Innovation
> Institute for Creativity, Arts, and Technology
>
> Virginia Tech
> Creative Technologies in Music
> School of Performing Arts – 0141
> Blacksburg, VA 24061
> (540) 231-6139
> ico at vt.edu
>
> www.icat.vt.edu
> www.performingarts.vt.edu
> l2ork.icat.vt.edu
> ico.bukvic.net
>