Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!udel!mmdf
From: bunnell@udel.edu (H Timothy Bunnell)
Newsgroups: comp.os.minix
Subject: (none)
Message-ID: <23804@louie.udel.EDU>
Date: 13 Sep 89 04:22:36 GMT
Sender: mmdf@udel.EDU
Lines: 42

The following short routine illustrates one version of a bug that I and
several other folks have encountered (e.g., in both the recent ls.c postings).
It was actually Earl Chew who fingered the problem in a response to patches to
his ls.  The bug crops up when a "static" is declared within a block that is
not also the the start of a function.  The example program compiles and goes
thru asld without error messages, but prints garbage for the first printf
while the second and third behave correctly.  In other cases such as the
recent ls postings, similar static declarations caused asld to punt with
obscure multiple declaration errors.

The effect of the bug is fairly obvious when looking at the compiler output.
In the example program, two variables are created for the code within the
scope of the if block.  Neither one contains the four bytes that should
initialize array3.  Instead, both variables point to the static area
containing the string arg for the printf.

The compiler I'm using is the ACK compiler supplied with Minix 1.2 for PCs.  I
have the impression that other versions of the ACK compiler do not share this
trait. This leads to a question: does anyone maintain a log of known
and/or suspected compiler bugs?  If so, perhaps it could be circulated
periodically.

Tim Bunnell <bunnell@henry.asel.udel.edu>
----------------------------cut here-----------------------------------------
/* Illustrates a bug when compiled with the Minix 1.2 ACK compiler */

#include <stdio.h>

static char array1[] = {'a', 'b', 'c', 'd'};

main ()
{
static char array2[] = {'1', '2', '3', '4'};
int bugpresent = 1;

	if (bugpresent) {
		static char array3[] = {'W', 'X', 'Y', 'Z'};
		printf("Array3[1] = %c\n", array3[1]);
	}
	printf("Array2[1] = %c\n", array2[1]);
	printf("Array1[1] = %c\n", array1[1]);
}