[pulseaudio-discuss] ABI breakage in introspect (85e7fbc196f4424f68e530c2e3a01d9b941f293e)

[Colin Guthrie]

[ Solved, Tanu is on the ball once again! Ignore the pointless patch (it
truely is pointless) ]

See below if you want more info.

'Twas brillig, and Tanu Kaskinen at 09/01/14 12:50 did gyre and gimble:
> On Thu, 2014-01-09 at 10:07 +0000, Colin Guthrie wrote:
>> Hi,
>>
>> In order to get Bluetooth support (at least A2DP) I've been tracking the
>> 5.0 release for Mageia (it's generally an unfortunate situation but such
>> is life).
>>
>> Sadly there appears to be some ABI breakage introduced related to card
>> profiles.
>>
>> This is purportedly fixed by the below commit but I think there are
>> still issues.
>>
>> I've had crashes reported in both KDE's kcm_phonon (the bits which which
>> I wrote) and pavucontrol directly, both related to updating card info.
>> It seems invalid string information is passed in to string compare
>> functions and they crash.
>>
>> https://bugs.mageia.org/show_bug.cgi?id=12155
> 
> Here's a snippet of the pavucontrol backtrace:
> 
> Program received signal SIGSEGV, Segmentation fault.
> __strcmp_ssse3 () at ../sysdeps/i386/i686/multiarch/strcmp-ssse3.S:240
> 240             movzbl  (%eax), %ecx
> (gdb) bt
> #0  __strcmp_ssse3 () at ../sysdeps/i386/i686/multiarch/strcmp-ssse3.S:240
> #1  0x0806daa0 in operator() (this=0xbfffe80c, lhs=..., lhs=..., rhs=..., 
>     rhs=...) at mainwindow.cc:43
> #2  _M_get_insert_unique_pos (__k=..., this=0xbfffe80c)
>     at /usr/include/c++/4.8.2/bits/stl_tree.h:1324
> #3  std::_Rb_tree<pa_card_profile_info, pa_card_profile_info, std::_Identity<pa_card_profile_info>, profile_prio_compare, std::allocator<pa_card_profile_info> >::_M_insert_unique (this=0xbfffe80c, __v=...)
>     at /usr/include/c++/4.8.2/bits/stl_tree.h:1377
> #4  0x08069947 in insert (__x=..., this=0xbfffe80c)
>     at /usr/include/c++/4.8.2/bits/stl_set.h:463
> #5  MainWindow::updateCard (this=0x822e688, info=...) at mainwindow.cc:319
> #6  0xb7422e33 in context_get_card_info_callback (pd=pd at entry=0x8133208, 
>     command=command at entry=2, tag=tag at entry=5, t=t at entry=0x825f930, 
>     userdata=userdata at entry=0x82c94f8) at pulse/introspect.c:971
> 
> One of the parameters of std::_Rb_tree is
> std::allocator<pa_card_profile_info>, and that looks like the data
> structure allocates pa_card_profile_info objects. That's not safe. It
> looks like pavucontrol is buggy.

Just out of interest, why is that not safe? Is allocating a struct not
safe in a set?

Various bits I've read seem to suggest this isn't a problem.

> void MainWindow::updateCard(const pa_card_info &info) {
>     ...
>     std::set<pa_card_profile_info,profile_prio_compare> profile_priorities;
> 
> The set should contain pointers, not whole profile info objects.

Using pointers seems somewhat counter-intuitive. By default the ordering
semantics would be on the pointer address which is pretty arbitrary
(although I accept that it's likely equally arbitrary with structs
without overloading the < operator, which we don't do anyway)

> Hmm... but pa_card_profile_info hasn't been modified in the current
> master compared to v4.0, so if pavucontrol was compiled against libpulse
> from v4.0, there should be no problem. Is it possible that pavucontrol
> was compiled against some earlier git snapshot in Mageia that had the
> available flag added to pa_card_profile_info, and now that the flag was
> removed, pavucontrol broke?

Yeah it was complied Sat 19 Oct 2013 00:02:08 BST, at which point the PA
itself was a 5.0 snapshot at f81e3e1d7852c05b4b737ac7dac4db95798f0117.

So thinking about it a bit more, I can see the problem and yes, you got
it bang on as f81e3e1d7852c05b4b737ac7dac4db95798f0117 included the ABI
break but not the fix! D'oh!!

Sorry for noise!

Thanks Tanu!

Col

-- 

Colin Guthrie
gmane(at)colin.guthr.ie
http://colin.guthr.ie/

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