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Date: Sun, 30 Sep 2012 17:26:49 -0700 From: Josh Triplett <josh@...htriplett.org> To: Daniel Santos <daniel.santos@...ox.com> Cc: LKML <linux-kernel@...r.kernel.org>, Andi Kleen <ak@...ux.intel.com>, Andrea Arcangeli <aarcange@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, Christopher Li <sparse@...isli.org>, David Daney <david.daney@...ium.com>, David Howells <dhowells@...hat.com>, Joe Perches <joe@...ches.com>, Konstantin Khlebnikov <khlebnikov@...nvz.org>, linux-sparse@...r.kernel.org, Michel Lespinasse <walken@...gle.com>, Paul Gortmaker <paul.gortmaker@...driver.com>, Pavel Pisa <pisa@....felk.cvut.cz>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Steven Rostedt <rostedt@...dmis.org> Subject: Re: [PATCH 8/10] bug.h: Make BUILD_BUG_ON generate compile-time error On Sun, Sep 30, 2012 at 06:29:01PM -0500, Daniel Santos wrote: > On 09/28/2012 09:55 PM, Josh Triplett wrote: > > Assuming you don't call BUILD_BUG_ON_MSG more than once per line: > > > > /tmp$ cat test.c > > #define BUILD_BUG_ON_MSG_INTERNAL2(cond, msg, line) \ > > do { \ > > extern void __build_bug_on_failed_ ## line (void) __attribute__((error(msg))); \ > > if (cond) \ > > __build_bug_on_failed_ ## line(); \ > > } while (0) > > > > #define BUILD_BUG_ON_MSG_INTERNAL(cond, msg, line) BUILD_BUG_ON_MSG_INTERNAL2(cond, msg, line) > > #define BUILD_BUG_ON_MSG(cond, msg) BUILD_BUG_ON_MSG_INTERNAL(cond, msg, __LINE__) > > > > void f(void) > > { > > BUILD_BUG_ON_MSG(0, "test 1"); > > BUILD_BUG_ON_MSG(1, "test 2"); > > BUILD_BUG_ON_MSG(0, "test 3"); > > BUILD_BUG_ON_MSG(1, "test 4"); > > } > > /tmp$ gcc -c test.c > > test.c: In function ‘f’: > > test.c:14:119: error: call to ‘__build_bug_on_failed_14’ declared with attribute error: test 2 > > test.c:16:119: error: call to ‘__build_bug_on_failed_16’ declared with attribute error: test 4 > Thanks! This is very nice! I've done a little more research and > discovered that there's also a __COUNTER__ macro that is available > in gcc 4.3+. Before I realized that it was only available in gcc > 4.3, I wrote this little macro: > > #define _CONCAT1(a, b) a##b > #define CONCAT(a, b) _CONCAT1(a, b) > > #ifdef __COUNTER__ > # define UNIQUIFY(prefix) CONCAT(prefix, __COUNTER__) > #else > # define UNIQUIFY(prefix) CONCAT(prefix, __LINE__) > #endif > > However, this could lead to code might compile on gcc 4.3+, but > not compile prior, so this is bad, right? Yes, as long as Linux continues to support prior GCC versions (currently anything 3.2 or newer), I'd suggest sticking with __LINE__ so that it consistently breaks if you use more than one BUILD_BUG_ON_MSG per line. Good to know that __COUNTER__ exists, though. Also, the name BUILD_BUG_ON_MSG seems wrong to me somehow; I keep parsing it as though something about the message causes the build bug. - Josh Triplett -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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