| Bug ID | 100077 |
|---|---|
| Summary | libdrm atomic_add_unless() may reverse return value meaning |
| Product | DRI |
| Version | unspecified |
| Hardware | x86-64 (AMD64) |
| OS | BSD (Others) |
| Status | NEW |
| Severity | normal |
| Priority | medium |
| Component | libdrm |
| Assignee | dri-devel@lists.freedesktop.org |
| Reporter | davshao@gmail.com |
atomic_add_unless() in libdrm xf86atomic.h may reverse the meaning
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 = atomic_read(v);
while (c != unless && (old = atomic_cmpxchg(v, c, c + add)) != c)
c = old;
- return c == unless;
+ return c != unless;
}
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