another bug in PDP-11 'ld'

[utzoo!decvax!pur-ee!bruner]

Someone here recently discovered another problem with the PDP-11 "ld".
While in the course of investigating it, I found several cases of
signed arithmetic in the compiler/assembler/loader.  Compile the files:

	f1.c:
		short junk[16383];

	f2.c:
		short junk[];
		main(){}

and everything works just great.  Now, change the 16383 to 16384 and
try again.  This time, the loader will complain that "junk" is
undefined.  I suspect that this occurs because it is using an "int"
rather than an "unsigned" to hold the size of ".comm" symbols.
If there is no explicit declaration of the storage (there is none
in the example above), the loader takes the maximum size of all
".comm" definitions.  In this case, the sizes that it compares are
zero (junk[]) and -32768, so the maximum size is zero and it appears
that the symbol is undefined.

You can't even get this far if you use a "char" array:

	char junk[32768];

because the compiler gets mad at the (apparently negative) constant
and says "Constant required".

You can force the array into the data segment by adding an initializer:

	short junk[16384] = {};

but the assembler gets mad at this because the compiler passes it
the code:

	.globl	_junk
	.data
	_junk:
	0
	.=.+100000

and it thinks you are trying to decrease "." (a forbidden operation)
by adding -32768.

--John Bruner
decvax!pur-ee!bruner
ucbvax!pur-ee!bruner