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2 The Assembler

This chapter describes the module-independent part of the assembler. It documents the options and extensions which are not specific to a certain target, syntax or output driver. Be sure to also read the chapters on the cpu-backend, syntax- and output-module you are using. They will likely contain important additional information like data-representation or additional options.

2.1 General Assembler Options

vasm is run from the command line using the following syntax: 

      vasm<target>_<syntax> [options] [sourcefile]

When the source file name is missing, then the assembler reads the source text from ‘stdin’ until EOF (end-of-file, which is CTRL-D in Unix shells, or CTRL-\ in AmigaOS shells). Note, that most debugging formats (DWARF, etc.) no longer work with such temporary source texts.

The following options are supported by the machine independent part of vasm:

‘-chklabels’

Issues a warning when a label matches a mnemonic or directive name in either upper or lower case.

‘-D<name>[=<expression>]’

Defines a symbol with the name <name> and assigns the value of the expression when given. The assigned value defaults to 1 otherwise.

‘-depend=<type>’

Print all dependencies while assembling the source with the given options. No output is generated. <type> may be the word ‘list’ for printing one file name in each new line, or ‘make’ for printing a sequence of file names on a single line, suitable for Makefiles. When the output file name is given by ‘-o outname’ then vasm will also print outname: in front of it. Note that in contrast to option ‘-dependall’ only relative include file dependencies will be listed (which is the common case).

‘-dependall=<type>’

Prints dependencies in the same way as ‘-depend’, but also prints all include files with absolute paths.

‘-depfile <filename>’

Used together with ‘-depend’ or ‘-dependall’ and instructs vasm to output all dependencies to a new file, instead of stdout. Additionally, code will be generated in parallel to the dependencies output.

‘-dwarf[=<version>]’

Automatically generate DWARF debugging sections, suitable for source level debugging. When the version specification is missing, DWARF V3 will be emitted. The only difference to V2 is that it creates a .debug_ranges section, with address ranges for all sections, instead of a bad workaround specifying DW_AT_low_pc=0 and DW_AT_high_pc=~0. Note, that when you build vasm from source, you may have to specify your host operating system with -Dname in the Makefile to include the appropriate code which can determine the current work directory. Otherwise the default would be to set the current work directory to an empty string. Currently supported are: AMIGA, ATARI, MSDOS, UNIX, _WIN32.

‘-esc’

Enable escape character sequences. This will make vasm treat the escape character \ in string constants similar as in the C language.

‘-F<fmt>’

Use module <fmt> as output driver. See the chapter on output drivers for available formats and options.

‘-I<path>’

Define another include path. They are searched in the order of occurrence on the command line, and always before any include paths defined in the source.

‘-ignore-mult-inc’

When the same file is included multiple times, using the same path, this is silently ignored, causing the file to be processed only once. Note, that you can still include the same file twice when using different paths to access it.

‘-L <listfile>’

Enables generation of a listing file and directs the output into the file <listfile>.

‘-Lall’

List all symbols, including unused equates. Default is to list all labels and all used expressions only.

‘-Lbpl=<n>’

Set the maximum number of bytes per line in a listing file to <n>. Defaults to 8 (fmt=wide).

‘-Lfmt=<fmt>’

Set the listing file format to <fmt>. Defaults to wide. Available are: wide, old.

‘-Llo’

Show only program labels in the sorted symbol listing. Default is to list all symbols, including absolute expressions.

‘-Lni’

Do not show included source files in the listing file (fmt=wide).

‘-Lns’

Do not include symbols in the listing file (fmt=wide).

‘-maxerrors=<n>’

Sets the maximum number of errors to display before assembly is aborted. When <n> is 0 then there is no limit. Defaults to 5.

‘-maxmacrecurs=<n>’

Defines the maximum number of recursion levels within a macro. Defaults to 1000.

‘-maxpasses=<n>’

Adjusts the maximum number of passes while resolving a section. Defaults to 1500.

‘-nocase’

Disables case-sensitivity for everything - identifiers, directives and instructions. Note that directives and instructions may already be case-insensitive by default in some modules.

‘-nocompdir’

Do not search for include files relative to the compile directory (where the main input source is located).

‘-noesc’

No escape character sequences. This will make vasm treat the escape character \ as any other character. Might be useful for compatibility.

‘-noialign’

Perform no automatic alignment for instructions. Note that unaligned instructions make your code crash when executed! Only set when you know what you are doing!

‘-nomsg=<n>’

Disable the informational message <n>. <n> has to be the number of a valid informational message, like an optimization message.

‘-nosym’

Strips all local symbols from the output file and doesn’t include any other symbols than those which are required for external linkage.

‘-nowarn=<n>’

Disable warning message <n>. <n> has to be the number of a valid warning message, otherwise an error is generated.

‘-o <ofile>’

Write the generated assembler output to <ofile> rather than ‘a.out’.

‘-pad=<value>’

The given padding value can be one or multiple bytes (up to the cpu-backend’s address size). It is used for alignment purposes and to fill gaps between absolute ORG sections in the binary output module. Defaults to a zero-byte.

‘-pic’

Try to generate position independent code. Every relocation entry is flagged by an error message.

‘-quiet’

Do not print the copyright notice and the final statistics.

‘-unnamed-sections’

Sections are no longer distinguished by their name, but only by their attributes. This has the effect that when defining a second section with a different name but same attributes as a first one, it will switch to the first, instead of starting a new section. Is set automatically, when using an output-module which doesn’t support section names. For example: aout, tos, xfile.

‘-unsshift’

The shift-right operator (>>) treats the value to shift as unsigned, which has the effect that only 0-bits are inserted on the left side. The number of bits in a value depend on the target address type (refer to the appropriate cpu module documentation).

‘-uspc=<value>’

Uninitialized memory regions, declared by "space" directives (.space in std-syntax, ds in mot-syntax, etc.) are filled with the given value. Defaults to zero.

‘-w’

Hide all warning messages.

‘-wfail’

The return code of vasm will no longer be 0 (success), when there was a warning. Errors always make the return code non-zero (failure).

‘-v’

Print version and copyright messages from the assembler and all its modules, then exit.

‘-x’

Show an error message, when referencing an undefined symbol. The default behaviour is to declare this symbol as externally defined.

Note, that while most options allow an argument without any separating blank, some others require it (e.g. ‘-o’ and ‘-L’).

2.2 Expressions

Standard expressions are usually evaluated by the main part of vasm rather than by one of the modules (unless this is necessary).

All expressions evaluated by the frontend are calculated in terms of target address values, i.e. the range depends on the backend. Constants which exceed the target address range may be supported by some backends up to 128 bits.

Backends also have the option to support floating point constants directly and convert them to a backend-specific format which is described in the backend’s documentation.

Warning: Be aware that the quality and precision of the backend’s floating point output depends on the combination of host- and backend-format! If you need absolute precision, encode the floating point constants yourself in binary.

The available operators include all those which are common in assembler as well as in C expressions.

C like operators:

Assembler like operators:

Up to version 1.4b the operators had the same precedence and associativity as in the C language. Newer versions have changed the operator priorities to comply with common assembler behaviour. The expression evaluation priorities, from highest to lowest, are:

  1. + - ! ~ (unary +/- sign, not, complement)
  2. << >> (shift left, shift right)
  3. & (bitwise and)
  4. ^ ~ (bitwise exclusive-or)
  5. | ! (bitwise inclusive-or)
  6. * / % // (multiply, divide, modulo)
  7. + - (plus, minus)
  8. < > <= >= (less, greater, less or equal, greater or equal)
  9. == = != <> (equality, inequality)
  10. && (logical and)
  11. || (logical or)

Operands are integral values of the target address type. They can either be specified as integer constants of different bases (see the documentation on the syntax module to see how the base is specified) or character constants. Character constants are introduced by ' or " and have to be terminated by the same character that started them.

Multiple characters are allowed and a constant is built according to the endianness of the target.

When the ‘-esc’ option was specified, or automatically enabled by a syntax module, vasm interprets escape character sequences as in the C language:

\\

Produces a single \.

\b

The bell character.

\f

Form feed.

\n

Line feed.

\r

Carriage return.

\t

Tabulator.

\"

Produces a single ".

\'

Produces a single '.

\e

Escape character (27).

\<octal-digits>

One character with the code specified by the digits as octal value.

\x<hexadecimal-digits>

One character with the code specified by the digits as hexadecimal value.

\X<hexadecimal-digits>

Same as \x.

Note, that the default behaviour of vasm has changed since V1.7! Escape sequence handling has been the default in older versions. This was changed to improve compatibility with other assemblers. Use ‘-esc’ to assemble sources with escape character sequences. It is still the default in the std syntax module, though.

2.3 Symbols

You can define as many symbols as your available memory permits. A symbol may have any length and can be of global or local scope. Internally, there are three types of symbols:

Expression

These symbols are usually not visible outside the source, unless they are explicitly exported.

Label

Labels are always addresses within a program section. By default they have local scope for the linker.

Imported

These symbols are externally defined and must be resolved by the linker.

2.4 Predefined Symbols

Beginning with vasm V1.5c at least one expression symbol is always defined to allow conditional assembly depending on the assembler being used: __VASM. Its value depends on the selected cpu module.

Since V1.8i there may be a second internal symbol which reflects the format of the paths in the host file system. Currently there may be one of:

__UNIXFS

Host file system uses Unix-style paths.

__MSDOSFS

Host file system uses MS-DOS-, Windows-, Atari-style paths.

__AMIGAFS

Host file system uses AmigaDOS-style paths.

Note that such a path-style symbol only depends on a -D option given while compiling vasm from source. Refer to the section about building vasm (Interface chapter) for a listing of all supported host OS options.

There may be other internal symbols, which are defined by the syntax- or by the cpu module.

2.5 Include Files

Vasm supports include files and defining include paths. Whether this functionality is available depends on the syntax module, which has to provide the appropriate directives.

On startup vasm defines one or two default include paths: the current work directory and, when the main source is not located there, the compile directory.

Include paths are searched in the following order:

  1. Current work directory.
  2. Compile directory (path to main source).
  3. Paths specified by ‘-I’ in the order of occurrence on the command line.
  4. Paths specified by directives in the source text (in the order of occurrence).

Additionally, all the relative paths, defined by ‘-I’ or directives, are first appended to the current work directory name, then to the compile directory name, while searching for an include file.

Searching for include files in paths based on the compile directory can be completely disabled by ‘-nocompdir’.

2.6 Macros

Macros are supported by vasm, but the directives for defining them have to be implemented in the syntax module. The assembler core supports 9 macro arguments by default to be passed in the operand field, which can be extended to any number by the syntax module. They can be referenced inside the macro either by name (\name) or by number (\1 to \9), or both, depending on the syntax module. Recursions and early exits are supported.

Refer to the selected syntax module for more details.

2.7 Structures

Vasm supports structures, but the directives for defining them have to be implemented in the syntax module.

2.8 Conditional Assembly

Has to be provided completely by the syntax module.

2.9 Known Problems

Some known module-independent problems of vasm at the moment:

2.10 Credits

All those who wrote parts of the vasm distribution, made suggestions, answered my questions, tested vasm, reported errors or were otherwise involved in the development of vasm (in descending alphabetical order, under work, not complete):

2.11 Error Messages

The frontend has the following error messages:

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