Bug#842513: vlc: immediate crash on launch on powerpc

[James Cowgill]

Control: tags -1 - help
Control: severity -1 important
Control: retitle -1 vlc: should prevent installation on powerpc G3

Hi,

On 30/10/16 00:16, Robert Ou wrote:
> On Sat, Oct 29, 2016 at 3:43 PM, James Cowgill <jcowgill at debian.org> wrote:
>> Control: tags -1 help
>> Control: severity -1 grave
>>
>> Hi,
>>
>> On 29/10/16 23:00, Robert Ou wrote:
>>> Package: src:vlc
>>> Version: 2.2.4-7
>>> Severity: normal
>>>
>>> Dear Maintainer,
>>>
>>> I decided I wanted to test the performance of Debian PowerPC on my
>>> ancient iMac, and I discovered that vlc will immediately crash with an
>>> illegal instruction right after showing the "Privacy and Network Access
>>> Policy" window and before showing the main window. The crashes look like
>>> the following:
>>>
>>> [ 1560.952016] vlc[997]: unhandled signal 4 at 0ea48f58 nip 0ea48f58 lr 0ea48f4c code 30001
>>
>> As powerpc is a release architecture, this bug is RC.
>>
>> I tried running vlc on partch. It managed to get further, but then
>> segfaulted inside QT so it's probably a separate issue. I also had to
>> run it in xvfb so it probably gets different results.
>>
>> Specifically what powerpc hardware do you have? Could you run vlc within
>> gdb to determine which instruction it SIGILLs on (try 'layout asm')?
> 
> I was testing on a first-generation iMac with a 333 MHz PowerPC 750
> (G3). Running vlc under gdb shows that the crash occurs in
> libqt4_plugin.so in QRect::adjusted. The crash occurs on a "lvx
> v0,r10,r5" opcode, which is an Altivec opcode. The G3 however does not
> support Altivec. Here is a backtrace and some more debug information:

This explains it. From the PowerPC FAQ:
https://wiki.debian.org/PowerPC/FAQ#VLC_crashes_on_startup._What.27s_up_with_that.3F

"
If VLC immediately crashes, it's probably because you're on a G3 and
VLC was compiled with Altivec instructions. To use VLC on a G3, you
must compile it with the configure option --disable-altivec.
"

Having said that, I think adding something to vlc's preinst to prevent
installation on systems without altivec would be a good idea here.

I'm not sure going through all the trouble of compiling vlc twice so it
works on the G3 is worth it here - especially since powerpc may not be
a release architecture in 24 hours...

Thanks,
James

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