vaxism /vak'sizm/ n.
A piece of code that exhibits vaxocentrism in critical areas. Compare
PC-ism, unixism.
Node:vaxocentrism, Next:vdiff, Previous:vaxism, Up:= V
=
vaxocentrism /vak`soh-sen'trizm/ n.
[analogy with `ethnocentrism'] A notional disease said to
afflict C programmers who persist in coding according to certain
assumptions that are valid (esp. under Unix) on VAXen but false elsewhere. Among these are:
The assumption that dereferencing a null pointer is safe
because it is all bits 0, and location 0 is readable and 0.
Problem: this may instead cause an illegal-address trap on
non-VAXen, and even on VAXen under OSes other than BSD Unix.
Usually this is an implicit assumption of sloppy code (forgetting
to check the pointer before using it), rather than deliberate
exploitation of a misfeature.
The assumption that characters are signed.
The assumption that a pointer to any one type can freely be
cast into a pointer to any other type. A stronger form of this is
the assumption that all pointers are the same size and format,
which means you don't have to worry about getting the casts or
types correct in calls. Problem: this fails on word-oriented
machines or others with multiple pointer formats.
The assumption that the parameters of a routine are stored in
memory, on a stack, contiguously, and in strictly ascending or
descending order. Problem: this fails on many RISC
architectures.
The assumption that pointer and integer types are the same
size, and that pointers can be stuffed into integer variables
(and vice-versa) and drawn back out without being truncated or
mangled. Problem: this fails on segmented architectures or
word-oriented machines with funny pointer formats.
The assumption that a data type of any size may begin at any
byte address in memory (for example, that you can freely
construct and dereference a pointer to a word- or greater-sized
object at an odd char address). Problem: this fails on many (esp.
RISC) architectures better optimized for HLL execution speed, and can cause an illegal
address fault or bus error.
The (related) assumption that there is no padding at the end
of types and that in an array you can thus step right from the
last byte of a previous component to the first byte of the next
one. This is not only machine- but compiler-dependent.
The assumption that memory address space is globally flat and
that the array reference foo[-1] is necessarily
valid. Problem: this fails at 0, or other places on
segment-addressed machines like Intel chips (yes, segmentation is
universally considered a brain-damaged way to design machines
(see moby), but that is a separate
issue).
The assumption that objects can be arbitrarily large with no
special considerations. Problem: this fails on segmented
architectures and under non-virtual-addressing environments.
The assumption that the stack can be as large as memory.
Problem: this fails on segmented architectures or almost anything
else without virtual addressing and a paged stack.
The assumption that bits and addressable units within an
object are ordered in the same way and that this order is a
constant of nature. Problem: this fails on big-endian machines.
The assumption that it is meaningful to compare pointers to
different objects not located within the same array, or to
objects of different types. Problem: the former fails on
segmented architectures, the latter on word-oriented machines or
others with multiple pointer formats.
The assumption that an int is 32 bits, or
(nearly equivalently) the assumption that sizeof(int) ==
sizeof(long). Problem: this fails on PDP-11s, 286-based
systems and even on 386 and 68000 systems under some compilers
(and on 64-bit systems like the Alpha, of course).
The assumption that argv[] is writable. Problem:
this fails in many embedded-systems C environments and even under
a few flavors of Unix.
Note that a programmer can validly be accused of vaxocentrism
even if he or she has never seen a VAX. Some of these assumptions
(esp. 2-5) were valid on the PDP-11, the original C machine, and
became endemic years before the VAX. The terms `vaxocentricity'
and `all-the-world's-a-VAX syndrome' have been used
synonymously.