Messages in this thread | | | Date | Tue, 28 Apr 2009 19:55:27 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 5/5] proc: export more page flags in /proc/kpageflags |
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On Wed, 29 Apr 2009 10:38:42 +0800 Wu Fengguang <fengguang.wu@intel.com> wrote:
> > > +#define kpf_copy_bit(uflags, kflags, visible, ubit, kbit) \ > > > + do { \ > > > + if (visible || genuine_linus()) \ > > > + uflags |= ((kflags >> kbit) & 1) << ubit; \ > > > + } while (0); > > > > Did this have to be implemented as a macro? > > > > It's bad, because it might or might not reference its argument, so if > > someone passes it an expression-with-side-effects, the end result is > > unpredictable. A C function is almost always preferable if possible. > > Just tried inline function, the code size is increased slightly: > > text data bss dec hex filename > macro 1804 128 0 1932 78c fs/proc/page.o > inline 1828 128 0 1956 7a4 fs/proc/page.o >
hm, I wonder why. Maybe it fixed a bug ;)
The code is effectively doing
if (expr1) something(); if (expr1) something_else(); if (expr1) something_else2();
etc. Obviously we _hope_ that the compiler turns that into
if (expr1) { something(); something_else(); something_else2(); }
for us, but it would be good to check...
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