Messages in this thread | | | Date | Sun, 22 Jul 2007 21:47:06 +0530 | From | "Satyam Sharma" <> | Subject | Re: [PATCH 1/1] i386: Geode's TSC is not neccessary to mark tu unstable |
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> > > On Sun, 15 Jul 2007 21:06:27 +0200 > > > Juergen Beisert <juergen127@kreuzholzen.de> wrote: > > > > Replace NSC/Cyrix specific chipset access macros by inlined functions. > > > > With the macros a line like this fails (and does nothing): > > > > setCx86(CX86_CCR2, getCx86(CX86_CCR2) | 0x88); > > > > With inlined functions this line will work as expected.
> > On Thursday 19 July 2007 03:02, Andrew Morton wrote: > > > > > > I don't get it. Why would the macros behave differently from inlined > > > functions?
> On Thu, 19 Jul 2007 08:49:05 +0200 > Juergen Beisert <juergen127@kreuzholzen.de> wrote: > > > > X86 magic. The access order is important. The first access must always be the > > offset at 0x22. This access enables the next access to 0x23 (data). If you do > > it in wrong order, it fails. With the macros you get something like 0x22, > > 0x22, 0x23, 0x23. With the inline functions 0x22,0x23,0x22,0x23.
On 7/19/07, Andres Salomon <dilinger@queued.net> wrote: > > Wow, that's a really cool bug; nice work! Don't forget to update > arch/i386/kernel/cpu/mtrr/state.c, though; it uses setCx86() as well. It needs > to include processor-cyrix.h.
On 7/19/07, Andi Kleen <ak@suse.de> wrote: > > It also needs some big fat comments
Ok, I was discussing macros-in-C on some other thread and got reminded about this one. Anyway, I don't really think there was anything weird / surprising about this case at all -- it's just another manifestation of the same age-old time-tested advise all our respective grandmothers have always given us:
Never pass arguments that have side-effects to macros.
Of course, ideally the user shouldn't even know that the API call he's using is a macro or a function -- which puts the onus upon the person who *wrote* that API to ensure that he doesn't write macros for what could, and should, easily be functions. Macros are generally evil and always horrible, all IMHO, of course.
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