Prepending _ in C external names necessary?

[Thomas H{meenaho]

In article <1232 at hpda.UUCP> davel at hpda.UUCP (Dave Lennert) writes:
>We're considering changing our C compiler to *not* prepend an underscore
>at the beginning of all external names (functions, variables).  Will this
>break things?  Are there reasons (technical/religious) that we should not
>do this?

I say don't do it!

In one particular C compiler I've seen one can produce perefectly good
C code that doesn't work when compiled!

Consider the following small example from a 68K machine running V7:

main(){
   extern long a7;	/* perfectly legal declaration */
   a7 = 0x1234;
}

As the variable a7 is declared as external the compiler doesn't allocate
any space for it but assumes it will be defined at link time.
If I compile this into assembler the resulting code looks something
like this:

main:
	link	a6,#0
	move.l	#0x1234,a7
	unlk	a6
	rts

As a7 is the stackpointer on a 68K the result will be at best unpredictable
with another program! Needless to say the behaviour is the same for any
legal register name.

-- 
Thomas Hameenaho, Dept. of Computer Science, Uppsala University, Sweden
Phone: +46 18 138650
UUCP: thomas at kuling.UUCP (...!{seismo,mcvax}!enea!kuling!thomas)