UNI_ASS(VI)

NAME
uni_ass - universal assembler/loader

SYNOPSIS
/usr/em/lib/machine_as [options] argument ...

DESCRIPTION
The universal assembler is a framework allowing easy generation of an assembler for any byte oriented machine. The framework includes common pseudo instructions for name definition, label usage, storage allocation and initialization and expression evaluation. The resulting program assembles and links assembly modules. Arguments may be flags, assembly language modules or libraries.
Flags are:

-d[n]
    Produce a listing on standard output, the octal number n is mainly used for debugging purposes. The default is 700. 500 and 600 give slightly different listings.

-s[n]
    Produce a human-readable symbol table on standard output. The default for n is 3. The value 2 causes a listing of only the symbols internal to the modules. The value 1 causes a listing of external symbols only.

-o  The argument following this flag is taken as the name of the resulting load file. The default name is a.out.

The assemblers assemble and link together assembly language modules machine from files and libraries, producing an a.out file.

Two different types of arguments are allowed:

1-  Assembly language modules
2-  UNIX archives, as maintained by arch(I). These archives must only contain assembly language modules with .define as their first statement.

Note that it is not possible to do a partial load; loading starts from assembly language and produces binary machine code. No symbol table and no relocation bits are produced.

SEGMENTS and TYPES
The statements allocating and initializing space, like instructions and some pseudo-instruction reserve that space in the current segment. The currently reigning type of segment is determined by one of the pseudo-instructions: .text, .data, .bss and .org. The assembler concatenates all space allocated in each of the text, data and bss segments. That is: every byte in a text segment is followed by another byte in the text segment except the last, of which there is only one in each program. The org segment differs from the other three in the sense that the assembler makes no attempt to concatenate pieces of org segments. Each .org pseudo-instruction has a parameter telling where it should start allocating space. In the final stages of the assembly the text, data and bss segments are concatenated in that order after the length of each segment has been made a multiple of a machine dependent constant. The first segment (text) starts at the location that is given as an argument to the .base pseudo-instruction. The default is 0.

The labels defined in a particular segment have the type of that segment, other types are: undefined and absolute. All variables that do not have a value have the type undefined, a good example is an unsatisfied external reference. Numbers have the type absolute. The type of expressions depends on both the operators and the operands used. Generally, but not always, the following rule holds: whenever one of the operands is absolute and the resulting type is that of the other operand. Not every operation is allowed on every combination of types, for example: it is not allowed to add two text values.

SYNTAX

letters
    Both upper and lower case may be used and are seen as different. The underscore '_' is considered to be a letter.

identifiers
    Identifiers are a sequence of letters and digits, starting with a letter or a period '.'. Only the first eight characters are remembered by the assemblers, identifiers with the same first eight characters are considered to be identical. Identifiers can, only once, receive a value through assignment or a label definition.

local labels
    Local labels consist of a single digit. They can only be defined in the label part of a statement and used anywhere an identifier is allowed. They can be redefined at will. Two forms of use exist: forward and backward references. The first consists of the digit followed by an f and refers to the first definition of that label following the reference. The second consists of the digit followed by an b and refers to the last definition of the label before the reference.

strings
    Strings are enclosed in single "'" or double """ quotes. The use of \ddd where ddd is an octal number and \n, \r, \t, \b and \f is allowed and has the same meaning as in the C language.

numbers
    Numbers are a sequence of letters and digits, starting with a digit. No difference is made between small and capital letters.
    The base of the number is determined in the following way:
    if the number ends with an 'h' it is hexadecimal else
        if the number starts with '0x' it is hexadecimal else
            if the number starts with '0' it is octal else
                it's decimal.
    Note that the number '0x10h' is an illegal hexadecimal number, because 'x' is an illegal hexadecimal digit. The number should be written as '0x10' or '10h'. The range of numbers depends on the machine. A rule of the thumb is that the width of the machine's registers the same is as the number of bits allowed in numbers.

expressions
    The following operators are recognized:

      op    type       action
       |    binary    bitwise or
       &    binary    bitwise and
       ^    binary    bitwise exclusive or
       +    binary    two's complement addition
       +    unary     no effect
       -    binary    two's complement subtraction
       -    unary     two's complement negation
       *    binary    two's complement multiplication
       /    binary    two's complement division
       %    binary    two's complement remainder
       ~    unary     one's complement negation

    The operator precedence is the same as in C.
    The operands allowed are: identifiers, numbers and expressions. The evaluation order can be changed using the brackets '[' and ']'.

comment
    The character '!' denotes the start of comment, every character up to the next newline is skipped. Exclamation marks in strings are not recognized as the start of comment.

statements
    Statements are separated by newlines and ';' and can be preceded by label definitions. Label definitions have the form "identifier~:" or "digit~:". Statements can be: empty, an assignment, an instruction or a pseudo-instruction.

assignment
    An assignment has the form:
            identifier = expression
    The identifier receives the value and type of the expression.

instruction
    The syntax of an instruction depends on the type of the target machine. An example of a assembly file is presented at the end of the document.

pseudo-instruction
    The identifiers mentioned in the list are exported and can be used in other modules. Used for modules that are to be part of a libary. The .define pseudo's should be the first in such modules. When scanning a module in a library the univeral assembler checks whether any of its unsatified external references is mentioned in a .define list. If so, it includes that module in the program. The identifiers mentioned in the list are exported and can be used in other modules. Initialize a sequence of bytes. This is not followed by automatic alignment. Initialize a sequence of shorts (2-byte values). This is not followed by automatic alignment. Initialize a sequence of longs (4-byte values). This is not followed by automatic alignment. Initialize a sequence of words. The number of bytes occupied by a word depends on the target machine. This is not followed by automatic alignment. Initialize a sequence of bytes with the value of the bytes in the string. This is not followed by automatic alignment. Initialize a sequence of bytes with the value of the bytes in the string and terminate this with an extra zero byte. This is not followed by automatic alignment. Adjust the current position to a multiple of the value of the expression. The default is the word-size of the target machine. Allocate the indicated amount of bytes. The expression must be absolute. Start an org segment with the location counter at the indicated value. The value of the expression must be absolute. Start an segment of the indicated type. Set the starting address of the first of the consecutive segments (text) to the value of the expression. The expression must be absolute. Stop with a fatal error message when the value of the expression is non-zero.

SEE ALSO
ack(I), arch(I), a.out(V)

EXAMPLE
An example of INtel 8086 assembly code.

	.define begbss
	.define hol0,.diverr,.reghp
	.define EIDIVZ
	EIDIVZ          = 6
	base            = 0x01C0
	topmem          = 0xFFF0
		.org    topmem-16
	.extern __n_line
	maxmem:
	__n_line:
		.space  16
		.errnz  __n_line-0xFFE0
		.base   base
		.text
		cld
		xor     ax,ax
		mov     (2),cs
		mov     (0),.diverr
		mov     sp,maxmem
		mov     di,begbss
		mov     cx,[[endbss-begbss]/2]&0x7FFF
		! xor     ax,ax ! ax still is 0
		rep stos
		mov     ax,1
		push    ax
		call    _start
	3:
		jmp	3b
	.diverr:
		push    ax
		mov     ax,EIDIVZ
		call    .error
		pop     ax
		iret
		cmp	0,4(bx)(di)	! just to show this addr. mode
		.data
	begdata:
	hol0:
		.word   0,0
		.word   0,0
		.word   3f
	.reghp:
		.word   endbss
	3:
		.asciz "PROGRAM"
	.sp 3

DIAGNOSTICS
Various diagnostics may be produced. The most likely errors, however, are unresolved references, probably caused by the omission of a library argument.

BUGS
The resulting a.out file contains no information about the size and starting address of the segments.
The resulting a.out file does not contain a symbol table.
The alignment might give rise to internal assertion errors when the alignment requestes is larger than the machine dependent segment alignment.
Identifiers declared as externals cannot be used as locals in any following module.