Date: Fri, 7 Sep 2007 14:50:21 +0300 From: Giorgos Keramidas <keramida@ceid.upatras.gr> To: Luigi Rizzo <rizzo@icir.org> Cc: current@freebsd.org Subject: Re: how to tell 64 vs 32 bit architecture ? Message-ID: <20070907115021.GA2718@kobe.laptop> In-Reply-To: <20070907000950.A91211@xorpc.icir.org> References: <20070906111028.A83649@xorpc.icir.org> <20070906222647.GB2737@kobe.laptop> <20070907000950.A91211@xorpc.icir.org>
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On 2007-09-07 00:09, Luigi Rizzo <rizzo@icir.org> wrote: >On Fri, Sep 07, 2007 at 01:26:47AM +0300, Giorgos Keramidas wrote: >>On 2007-09-06 11:10, Luigi Rizzo <rizzo@icir.org> wrote: >>> hi, >>> i was wondering what is the proper way to tell a 64 vs 32 bit >>> architecture. >>> >>> I see that some code in sys/ uses ' #ifdef __LP64__ ' but i am not >>> sure if this is generic enough (ie not gcc or FreeBSD specific), >>> and also suitable for userland (i.e. works on linux or other platforms >>> as well). >> >> This is usually needed to differentiate between a feature "X" which >> behaves differently in amd64 vs. i386 vs. sparc vs. sparc64, etc. > > i am actually looking at pointer sizes, as i need to do some pointer > manipulation going through intptr_t, and need to know that in the > preprocessor because some constants need to be 32 or 64 bit depending > on that, and are not trivial (i.e. not 0, 1 or something i can build > with size-agnostic expressions) An intptr_t can safely hold any void pointer value, and C99 says: % 7.18.1.4 Integer types capable of holding object pointers % % 1 The following type designates a signed integer type with the % property that any valid pointer to void can be converted to % this type, then converted back to pointer to void, and the % result will compare equal to the original pointer: % % intptr_t What sort of manipulation? Can this sort of manipulation be written in a way that uses sizeof(intptr_t) instead of 4, 8, or preprocessor magic? If not, then I can't think of any cross-compiler and cross-platform way to check in the preprocessor, and you may have to resort to custom checks (i.e. like those written in autoconf scripts) :-( - Giorgos
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