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-11}s, 286-based systems and even on 386 and 68000
    systems under some compilers (and on 64-bit systems like the
    Alpha, of course).
   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.
    

vaxocentrism

   /vak"soh-sen"trizm/ [analogy with "ethnocentrism"] A notional
   disease said to afflict C programmers who persist in coding
   according to certain assumptions that are valid (especially
   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 (especially RISC) architectures better optimised
   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}, {Intel
   80286}-based systems and even on {Intel 80386} and {Motorola
   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 flavours 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 (especially 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.

   [{Jargon File}]