mpv, ffmpeg seg fault in macOS catalina

Gill Bates smogus at
Fri Oct 18 13:56:21 UTC 2019

Thanks all for the explanations and workaround. 

From: "Mojca Miklavec" <mojca at> 
To: "smogus" <smogus at> 
Cc: "macports-users" <macports-users at> 
Sent: Friday, October 18, 2019 5:02:55 AM 
Subject: Re: mpv, ffmpeg seg fault in macOS catalina 

V čet., 17. okt. 2019 22:58 je oseba Gill Bates < [ mailto:smogus at | smogus at ] > napisala: 

I recently updated to catalina (10.15) and Xcode (11.1), installed MacPorts from source (2.6.1) and had it build mpv and its dependencies. However, mpv (and ffmpeg for example) do not run apparently related to some new default compiler option enforcing 16 byte stack alignment? See: 
[ | ] 
[ | ] 
[ | ] 

I first saw [ | ] , but that one eventually leads to the same thread linked above. 


The advice seems to be to revert Xcode but will rebuilding everything with Xcode 10.3 on macos 10.15 really be a workaround? Or is a better choice to modify portfiles to include the CFLAG option to disable stack checks as mentioned in the linked posts and use Xcode 11.1? 


Workaround is to either blacklist the compiler which has this option turned on by default (which is what Chris replied) or in fact use a flag to disable this. But disabling this flag is not needed for non-broken compilers, so it's probably better to just blacklist the compiler, and the latest compiler with be automatically used again when the bug gets fixed. 


"Part B" is a question for my understanding, is this a really an Xcode/compiler issue or a problem with the source software packages? 


I would say that this is in fact an issue with the compiler. As they said, the bug has been present before, it's just that nobody noticed it until it was switched on by default. I've seen an email saying that this is likely to be fixed in one of the next Xcode updates, so it's just a matter of time. 

I believe this affects only source code which uses some heavy optimisations, which is why you would not see it in most of the software where high performance is not crucially important for the functionality. 


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