Re: function start address allignment

Article View: comp.sys.intel

Article #1883

#1883

From: Phil Barrett
Date: Fri, 03 Mar 1989 01:42

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In article <687@pcrat.UUCP> rick@pcrat.UUCP (Rick Richardson) writes:
>In article <311@ssp2.idca.tds.philips.nl> pb@idca.tds.PHILIPS.nl (Peter Brouwer) writes:
>>When looking at executables with sdb and dis (unix) I noticed that the
>>start of a function in a c program is always word alligned. If
>
>I think this is due to the Basic-16 ... iAPX286 ... iAPX386 heritage
>of the compiler.  Basic-16 had a mechanism known as transfer vectors

Actually, I believe the reason is performance. The 386 needs to have fetched
the entire instruction before it can begin execution of it.  By aligning
the target of a control transfer, you can minimize the number of DWord fetches
required to start execution of the instruction and thus improve the performance
of your program.

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References: <311@ssp2.idca.tds.philips.nl> <687@pcrat.UUCP>

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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!unmvax!pprg.unm.edu!hc!lll-winken!uunet!microsoft!philba
From: philba@microsoft.UUCP (Phil Barrett)
Newsgroups: comp.sys.intel
Subject: Re: function start address allignment
Keywords: word alignment
Message-ID: <795@microsoft.UUCP>
Date: 3 Mar 89 01:42:26 GMT
References: <311@ssp2.idca.tds.philips.nl> <687@pcrat.UUCP>
Reply-To: philba@microsoft.UUCP (Phil Barrett)
Organization: Microsoft Corp., Redmond WA
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