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Date: Mon, 19 Oct 2009 11:19:29 -0700
From: Hollis Blanchard <hollisb@...ibm.com>
To: Jan Beulich <JBeulich@...ell.com>
Cc: sfr@...b.auug.org.au, akpm@...ux-foundation.org,
linuxppc-dev@...ts.ozlabs.org,
Rusty Russell <rusty@...tcorp.com.au>, kvm-ppc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-next@...r.kernel.org
Subject: Re: linux-next: tree build failure
On Thu, 2009-10-15 at 08:27 +0100, Jan Beulich wrote:
> >>> Hollis Blanchard <hollisb@...ibm.com> 15.10.09 00:57 >>>
> >On Fri, 2009-10-09 at 12:14 -0700, Hollis Blanchard wrote:
> >> Rusty's version of BUILD_BUG_ON() does indeed fix the build break, and
> >> also exposes the bug in kvmppc_account_exit_stat(). So to recap:
> >>
> >> original: built but didn't work
> >> Jan's: doesn't build
> >> Rusty's: builds and works
> >>
> >> Where do you want to go from here?
> >
> >Jan, what are your thoughts? Your BUILD_BUG_ON patch has broken the
> >build, and we still need to fix it.
>
> My perspective is that it just uncovered already existing brokenness. And
> honestly, I won't be able to get to look into this within the next days. (And
> btw., when I run into issues with other people's code changes, quite
> frequently I'm told to propose a patch, so I'm also having some
> philosophical problem understanding why I can't simply expect the same
> when people run into issues with changes I made, especially in cases like
> this where it wasn't me introducing the broken code.) So, if this can wait
> for a couple of days, I can try to find time to look into this. Otherwise, I'd
> rely on someone running into the actual issue to implement a solution.
Sorry, I thought it was clear, but to be more explicit: I propose the
following patch, which replaces the current BUILD_BUG_ON implementation
with Rusty's version.
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -677,18 +677,19 @@ struct sysinfo {
char _f[20-2*sizeof(long)-sizeof(int)]; /* Padding: libc5 uses this.. */
};
-/* Force a compilation error if condition is true */
-#define BUILD_BUG_ON(condition) ((void)BUILD_BUG_ON_ZERO(condition))
-
-/* Force a compilation error if condition is constant and true */
-#define MAYBE_BUILD_BUG_ON(cond) ((void)sizeof(char[1 - 2 * !!(cond)]))
-
-/* Force a compilation error if condition is true, but also produce a
- result (of value 0 and type size_t), so the expression can be used
- e.g. in a structure initializer (or where-ever else comma expressions
- aren't permitted). */
-#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
-#define BUILD_BUG_ON_NULL(e) ((void *)sizeof(struct { int:-!!(e); }))
+#ifndef __OPTIMIZE__
+#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
+#else
+/* If it's a constant, catch it at compile time, otherwise at link time. */
+extern int __build_bug_on_failed;
+#define BUILD_BUG_ON_ZERO(e) (sizeof(char[1 - 2 * !!(e)]) - 1)
+#define BUILD_BUG_ON(condition) \
+ do { \
+ ((void)sizeof(char[1 - 2*!!(condition)])); \
+ if (condition) __build_bug_on_failed = 1; \
+ } while(0)
+#define MAYBE_BUILD_BUG_ON(condition) BUILD_BUG_ON(condition)
+#endif
/* Trap pasters of __FUNCTION__ at compile-time */
#define __FUNCTION__ (__func__)
--
Hollis Blanchard
IBM Linux Technology Center
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