Date: Sun, 22 Jul 2012 19:51:56 GMT From: Ariane van der Steldt <ariane@stack.nl> To: freebsd-gnats-submit@FreeBSD.org Subject: threads/170073: stdatomic.h doesn't use clang builtings for C Message-ID: <201207221951.q6MJpuZl071441@red.freebsd.org> Resent-Message-ID: <201207222000.q6MK0IMo040590@freefall.freebsd.org>
next in thread | raw e-mail | index | archive | help
>Number: 170073
>Category: threads
>Synopsis: stdatomic.h doesn't use clang builtings for C
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-threads
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Sun Jul 22 20:00:18 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator: Ariane van der Steldt
>Release: freebsd HEAD
>Organization:
>Environment:
FreeBSD mud.stack.nl 9.0-STABLE FreeBSD 9.0-STABLE #0: Thu Jun 14 13:51:30 CEST 2012 root@mud.stack.nl:/usr/obj/usr/src/sys/GENERIC amd64
>Description:
First a little disclaimer: I tested this with clang-3.1 on bitrig. The freebsd I ran this on is using clang-3.0 which does returns 0 for the c{,xx}_atomic feature/extension.
stdatomic.h tests for __has_feature(cxx_atomic) which is only true when compiling in c++11 mode.
However since stdatomic.h is a C header file, it should also work in c11 mode.
Running:
echo '__has_feature(cxx_atomic)' | clang-3.1 -x c -std=c11 -E -
yields 0, while running:
echo '__has_feature(c_atomic)' | clang-3.1 -x c -std=c11 -E -
yields 1.
In addition, I'm contemplating if __has_feature should be replaced by __has_extension, so that non-c11 code can also include stdatomic.h.
>How-To-Repeat:
Run the clang 3.1 preprocessor on stdatomic.h for C code and it will use the GNU counterparts of the contained code. Running the same code through the clang++ 3.1 preprocessor yields the clang counterpart of the code.
>Fix:
See provided diff below, using __has_extension instead of __has_feature.
This also requires a compatibility define in sys/cdefs.h:
#ifndef __has_extension
#define __has_extension(x) 0
#endif
diff --git a/include/stdatomic.h b/include/stdatomic.h
index b0d1ea9..89f77dd 100644
--- a/include/stdatomic.h
+++ b/include/stdatomic.h
@@ -33,7 +33,7 @@
#include <sys/cdefs.h>
#include <sys/_types.h>
-#if __has_feature(cxx_atomic)
+#if __has_extension(c_atomic) || __has_extension(cxx_atomic)
#define __CLANG_ATOMICS
#elif __GNUC_PREREQ__(4, 7)
#define __GNUC_ATOMICS
>Release-Note:
>Audit-Trail:
>Unformatted:
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201207221951.q6MJpuZl071441>