Chapter 40. VAX Dependent Features

40.1. VAX Command-Line Options

The Vax version of as accepts any of the following options, gives a warning message that the option was ignored and proceeds. These options are for compatibility with scripts designed for other people's assemblers.

-D (Debug), -S (Symbol Table), -T (Token Trace)

These are obsolete options used to debug old assemblers.

-d (Displacement size for JUMPs)

This option expects a number following the -d. Like options that expect filenames, the number may immediately follow the -d (old standard) or constitute the whole of the command line argument that follows -d (gnu standard).

-V (Virtualize Interpass Temporary File)

Some other assemblers use a temporary file. This option commanded them to keep the information in active memory rather than in a disk file. as always does this, so this option is redundant.

-J (JUMPify Longer Branches)

Many 32-bit computers permit a variety of branch instructions to do the same job. Some of these instructions are short (and fast) but have a limited range; others are long (and slow) but can branch anywhere in virtual memory. Often there are 3 flavors of branch: short, medium and long. Some other assemblers would emit short and medium branches, unless told by this option to emit short and long branches.

-t (Temporary File Directory)

Some other assemblers may use a temporary file, and this option takes a filename being the directory to site the temporary file. Since as does not use a temporary disk file, this option makes no difference. -t needs exactly one filename.

The Vax version of the assembler accepts additional options when compiled for VMS:

-h n

External symbol or section (used for global variables) names are not case sensitive on VAX/VMS and always mapped to upper case. This is contrary to the C language definition which explicitly distinguishes upper and lower case. To implement a standard conforming C compiler, names must be changed (mapped) to preserve the case information. The default mapping is to convert all lower case characters to uppercase and adding an underscore followed by a 6 digit hex value, representing a 24 digit binary value. The one digits in the binary value represent which characters are uppercase in the original symbol name.

The -h n option determines how we map names. This takes several values. No -h switch at all allows case hacking as described above. A value of zero (-h0) implies names should be upper case, and inhibits the case hack. A value of 2 (-h2) implies names should be all lower case, with no case hack. A value of 3 (-h3) implies that case should be preserved. The value 1 is unused. The -H option directs as to display every mapped symbol during assembly.

Symbols whose names include a dollar sign $ are exceptions to the general name mapping. These symbols are normally only used to reference VMS library names. Such symbols are always mapped to upper case.


The -+ option causes as to truncate any symbol name larger than 31 characters. The -+ option also prevents some code following the _main symbol normally added to make the object file compatible with Vax-11 "C".


This option is ignored for backward compatibility with as version 1.x.


The -H option causes as to print every symbol which was changed by case mapping.