atomic_add_unless() in libdrm xf86atomic.h may reverse the mea=
ning
of its return value.
Linux kernel documentation seems to indicate something like:
"Returns non-zero if @v was not @u, and zero otherwise."
A simple inverting the meaning of libdrm's return value
allowed glxgears to properly function for a hacked version
of pkgsrc on DragonFly 4.7-DEVELOPMENT on an Intel IvyBridge
integrated graphics machine. glxgears was already properly
functioning on the same machine for NetBSD current, NetBSD
using its own atomic operations declared in its sys/atomic.h
header.
A one line (character) fix is of the form:
--- xf86atomic.h.orig 2015-09-22 04:34:51.000000000 +0000
+++ xf86atomic.h
@@ -111,7 +111,7 @@ static inline int atomic_add_unless(atom
c =3D atomic_read(v);
while (c !=3D unless && (old =3D atomic_cmpxchg(v, c, c + a=
dd)) !=3D c)
c =3D old;
- return c =3D=3D unless;
+ return c !=3D unless;
}