| Message ID | 1352844821-18952-6-git-send-email-daniel.santos@pobox.com (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On Tue, Nov 13, 2012 at 04:13:38PM -0600, danielfsantos@att.net wrote: > When calling BUILD_BUG_ON in an optimized build using gcc 4.3 and later, > the condition will be evaulated twice, possibily with side-effects. > This patch eliminates that error. > > Signed-off-by: Daniel Santos <daniel.santos@pobox.com> > --- > include/linux/bug.h | 5 +++-- > 1 files changed, 3 insertions(+), 2 deletions(-) > > diff --git a/include/linux/bug.h b/include/linux/bug.h > index 1b2465d..ccd44ce 100644 > --- a/include/linux/bug.h > +++ b/include/linux/bug.h > @@ -58,8 +58,9 @@ struct pt_regs; > extern int __build_bug_on_failed; > #define BUILD_BUG_ON(condition) \ > do { \ > - ((void)sizeof(char[1 - 2*!!(condition)])); \ > - if (condition) __build_bug_on_failed = 1; \ > + bool __cond = !!(condition); \ > + ((void)sizeof(char[1 - 2*!!(__cond)])); \ No need for the !!(__cond) here because you've done it in the line above. IOW, bool __cond = !!(condition); ((void)sizeof(char[1 - 2 * __cond])); which is even a bit more readable, as a matter of fact. > + if (__cond) __build_bug_on_failed = 1; \ > } while(0) > #endif Thanks.
On 11/15/2012 09:07 AM, Borislav Petkov wrote: > On Tue, Nov 13, 2012 at 04:13:38PM -0600, danielfsantos@att.net wrote: >> When calling BUILD_BUG_ON in an optimized build using gcc 4.3 and later, >> the condition will be evaulated twice, possibily with side-effects. >> This patch eliminates that error. >> >> Signed-off-by: Daniel Santos <daniel.santos@pobox.com> >> --- >> include/linux/bug.h | 5 +++-- >> 1 files changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/include/linux/bug.h b/include/linux/bug.h >> index 1b2465d..ccd44ce 100644 >> --- a/include/linux/bug.h >> +++ b/include/linux/bug.h >> @@ -58,8 +58,9 @@ struct pt_regs; >> extern int __build_bug_on_failed; >> #define BUILD_BUG_ON(condition) \ >> do { \ >> - ((void)sizeof(char[1 - 2*!!(condition)])); \ >> - if (condition) __build_bug_on_failed = 1; \ >> + bool __cond = !!(condition); \ >> + ((void)sizeof(char[1 - 2*!!(__cond)])); \ > No need for the !!(__cond) here because you've done it in the line > above. IOW, > > bool __cond = !!(condition); > ((void)sizeof(char[1 - 2 * __cond])); > > which is even a bit more readable, as a matter of fact. Ah yes. I did notice that at one point, but I think it slipped my mind. Also, the kernel has introduced me to the usage of the !! construct, of which I'm well versed in its affects in various situations and how gcc's optimizer ends up treating its usage, so probably another reason I didn't change it immediately. But it's basically shorthand for the expression (condition ? 1 : 0), correct? Or are there other details in the C standard that makes it different in some cases? Thanks, Daniel -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Nov 15, 2012 at 01:11:15PM -0600, Daniel Santos wrote: > Ah yes. I did notice that at one point, but I think it slipped > my mind. Also, the kernel has introduced me to the usage of the > !! construct, of which I'm well versed in its affects in various > situations and how gcc's optimizer ends up treating its usage, so > probably another reason I didn't change it immediately. But it's > basically shorthand for the expression (condition ? 1 : 0), correct? I don't think so: "!!" is simply a double negation which turns the whatever wild construct you have into either 0 or 1, depending on what it evaluates to. But I don't know what the standard says so you'll have to check :-) Thanks.
diff --git a/include/linux/bug.h b/include/linux/bug.h index 1b2465d..ccd44ce 100644 --- a/include/linux/bug.h +++ b/include/linux/bug.h @@ -58,8 +58,9 @@ struct pt_regs; extern int __build_bug_on_failed; #define BUILD_BUG_ON(condition) \ do { \ - ((void)sizeof(char[1 - 2*!!(condition)])); \ - if (condition) __build_bug_on_failed = 1; \ + bool __cond = !!(condition); \ + ((void)sizeof(char[1 - 2*!!(__cond)])); \ + if (__cond) __build_bug_on_failed = 1; \ } while(0) #endif
When calling BUILD_BUG_ON in an optimized build using gcc 4.3 and later, the condition will be evaulated twice, possibily with side-effects. This patch eliminates that error. Signed-off-by: Daniel Santos <daniel.santos@pobox.com> --- include/linux/bug.h | 5 +++-- 1 files changed, 3 insertions(+), 2 deletions(-)