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Date: Thu, 30 Jun 2016 09:38:28 -0400
From: Rich Felker <>
Subject: Re: Issues when building libcxx libcxxabi with MUSL

On Thu, Jun 30, 2016 at 02:50:14PM +0200, Julien Ramseier wrote:
> > Le 22 juin 2016 à 21:41, Rich Felker <> a écrit :
> > 
> > On Wed, Jun 22, 2016 at 09:38:17PM +0200, Julien Ramseier wrote:
> >> Hi Zhao,
> >> 
> >> Not sure how you did build llvm-libcxx, but the only issue I encountered myself is
> >> the use of PTHREAD_MUTEX_INITIALIZER in libcxx include/__mutex_base.
> >> musl uses volatile types in its pthread_mutex_t struct and C++11 does not allow them
> >> with constexpr member initializers. This rule has been relaxed in C++14.
> > 
> > Note that the code using them is still formally/conceptually buggy.
> > POSIX does not permit using these initializers as values. They can
> > only be used as initializers for objects with static storage duration.
> > A "mutex value" makes no sense; mutexes are objects not values.
> Actually the latest POSIX spec allows it.
> See <>

Could you cite the specific text you're looking at? The requirement of
static storage was removed by but I see nothing allowing
the use of mutex values or assigning one to another, which as I
understand it is what the offending libc++ code is doing.

> A workaround for the C++11 constexpr issue should land soon in libcxx trunk.
> <>

I'm not very good at reading modern C++, but that looks like an actual
fix, not a workaround.


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