vaxocentrism

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:

  1. 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.

  2. The assumption that characters are signed.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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).

  9. The assumption that objects can be arbitrarily large with no
     special considerations.  Problem: this fails on segmented
     architectures and under non-virtual-addressing environments.

 10. 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.

 11. 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.

 12. 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.

 13. 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.

 14. 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.