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Path: utzoo!watmath!clyde!rutgers!lll-lcc!well!msudoc!crlt!michael
From: michael@crlt.UUCP
Newsgroups: comp.arch
Subject: Re: Abusing pointers (was: Available no. of registers)
Message-ID: <646@crlt.UUCP>
Date: Fri, 20-Feb-87 13:45:10 EST
Article-I.D.: crlt.646
Posted: Fri Feb 20 13:45:10 1987
Date-Received: Sun, 22-Feb-87 10:44:17 EST
References: <749@cullvax.UUCP>
Organization: McClary Associates, Ann Arbor MI
Lines: 37
Summary: Oh, really?  Where did they say so?

In article <1029@cuuxb.UUCP>, mwm@cuuxb.UUCP (Marc W. Mengel) writes:
+> Unfortunately, you don't have to take the address of a given variable
+> to use it, you merely have to take the address of a variable near it
+> and add an offset to it.  The way C is defined, this is quite legal.
+> 
+> For example, suppose I have a function f, declared as follows:
+> 	f(p)
+> 		struct { int a, b, c; } *p;
+> 	{
+> 	...
+> 	}
+> And I call it as follows:
+> 	b()
+> 	{
+> 		int a, b, c;
+> 
+> 		f( &a );
+> 	}
+> According to our venerable friends kerningham&ritchie, this is legal;
+> it is also used to some great extent in the older (v6 & v7) unix kernels.

I have heard that this is used in a number of kernels, and of course it
would work in a lot of compiler-generated code that didn't do tricks with
registers or storage allocation, and didn't waste a lot of processor and
programmer effort trying to "protect" you against your folly, but where
do K&R come out and say it is legal?  I just re-read the source I think
would be the most likely place (the "pointers" chapter of the sky-blue
C book) and didn't find it.

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