+.TL
+Assembler Reference Manual
+.AU
+John F. Reiser
+.AI
+.HO
+.AU
+Robert R. Henry\s-2\u*\d\s+2
+.FS
+\&\s-2\u*\d\s+2
+Preparation of this paper supported in part
+by the National Science Foundation under grant MCS # 78-07291.
+.FE
+.AI
+Electronics Research Laboratory
+University of California
+Berkeley, CA 94720
+.ND November 5, 1979
+.NH
+Introduction
+.PP
+This document describes the usage and input syntax
+of the \s8UNIX VAX\s10-11 assembler \fIas\fP.
+\fIAs\fP is designed for assembling the code produced by the
+C compiler; certain concessions have been made to handle code written
+directly by people, but in general little sympathy has been extended.
+This document is intended only for the writer of a compiler or a maintainer
+of the assembler.
+.NH
+Usage
+.PP
+\fIas\fP is used as follows:
+.in +5
+as
+[ \fB\-LVWJR\fR ]
+[ \fB\-d\fIn\fR ]
+[ \fB\-DTC\fR ]
+[ \fB\-t \fIdirectory\fR ]
+[ \fB\-o \fIoutput\fR ]
+[ \fIname\d\s-2\&1\s+2\u1\fP ]
+[ \fIname\d\s-2\&2\s+2\u ... \fP ]
+.br
+.in -5
+.PP
+The \fB\-L\fP flag instructs the assembler to save labels beginning with
+a 'L' in the symbol table portion output file.
+Labels are not saved by default, as the default action of the link
+editor \fIld\fP is to discard them anyway.
+.PP
+The \fB\-V\fP flag tells the assembler to place its interpass temporary
+file into virtual memory.
+In normal circumstances, the system manager
+will decide where the temporary file should lie.
+Our experiments
+with very large temporary files show that placing the temporary
+file into virtual memory will save about 13% of the assembly time,
+where the size of the temporary file is about 350K bytes.
+Most assembler sources will not be this long.
+.PP
+The \fB\-W\fP turns off reporting all errors.
+.PP
+The \fB\-J\fP flag forces \s-2UNIX\s+2 style pseudo\-branch
+instructions with destinations further away than a
+byte displacement to be
+turned into jump instructions with 4 byte offsets.
+The \fB\-J\fP flag buys you nothing if \fB\-d2\fP is set.
+(See \(sc 9.4)
+.PP
+The \fB\-R\fP flag effectively turns \fB.data\fP\fI n\fP
+segment changing directives into \fB.text\fP\fI n\fP directives.
+This obviates the need to run editor scripts on assembler source
+to ``read\-only'' fix initialized data segments.
+Uninitialized data (via \fB.lcomm\fP and \fP.comm\fP directives)
+is still assembled into the data or bss segments.
+.PP
+The \fB\-d\fP flag specifies the number of bytes
+which the assembler should allow for a displacement when the value of the
+displacement expression is undefined in the first pass.
+The possible values of \fIn\fP are 1, 2, or 4; the assembler uses 4 bytes
+if \fB-d\fP is not specified.
+See \(sc 9.2.
+.PP
+Provided the \fB\-V\fP flag is not set,
+the \fB\-t\fP flag causes the assembler to place its single temporary file
+in the \fIdirectory\fP instead of in \fI/tmp\fP.
+.PP
+The \fB\-o\fP flag causes the output to be placed on the named file.
+The output of the assembler is by default placed on
+the file \fIa.out\fR in the current directory.
+.PP
+The input to the assembler is normally taken from the standard input.
+If file arguments occurs, then the input is taken
+sequentially from the files \fIname\d\s-2\&1\s+2\u\fP,
+\fIname\d\s-2\&2\s+2\u\fP...
+This is not to say that the files are assembled seperately;
+\fIname\d\s-2\&2\s+2\u\fP
+is effectively concatenated to \fIname\d\s-2\&1\s+2\u\fP,
+so multiple definitions cannot occur amongst the input sources.
+.PP
+The \fB\-D\fP flag enables debugging information, provided that the
+assembler has been compiled to have debugging information available.
+.PP
+The \fB\-T\fP flag enables a trace to be generate of each token read
+by \fIas\fP to be printed. This is long and boring, but useful when
+debugging the assembler.
+.NH
+Lexical conventions
+.PP
+Assembler tokens include identifiers (alternatively, ``symbols'' or ``names''),
+constants, and operators.
+.NH
+Identifiers
+.PP
+An identifier consists of a sequence of alphanumeric characters (including
+period ``\|\fB.\fR\|'',
+underscore ``\(ul'' and
+dollar ``\|$\|'')
+of which the first may not be numeric.
+If the assembler has been compiled to support flexible length symbols,
+identifiers may be (practically) arbitrarily long with all
+characters significant;
+otherwise, only the first NCPS
+(a symbol defined in \fI/usr/include/a.out.h\fP, and normally 8)
+characters are significant.
+.NH 2
+Constants
+.NH 3
+Simple constants
+.PP
+All integer constants are 64 bits wide and interpreted as two's
+complement numbers.
+64 bit wide integer constants (quads) are only partially supported
+by the \s-2VAX\s+2 hardware, and are supported only to provide
+immediate constants to \s-2VAX\s+2 instructions with quad operands.
+Floating-point constants are 64 bits wide.
+The digits are ``0123456789abcdefABCDEF'' with the obvious values.
+.PP
+An octal constant consists of a sequence of digits with a leading zero.
+.PP
+A decimal constant consists of a sequence of digits without a leading zero.
+.PP
+A hexadecimal constant consists of the characters ``0x'' (or ``0X'')
+followed by a sequence of digits.
+.PP
+A single-character constant consists of a single quote ``\|\(fm\|''
+followed by an \s8ASCII\s10 character, including \s8ASCII\s10 newline.
+The constant's value is the code for the
+given character.
+.PP
+A floating-point constant consists of the characters ``0f'', ``0d'',
+``0F'', or ``0D'' followed by a sequence of characters which \fIatof\fP
+will recognize as a floating-point number;
+either ``e'', ``E'', ``d''or ``D''
+may be used to designate the exponent field.
+.NH 3
+String Constants
+.PP
+A string constant is defined using the same syntax and semantics as ``C''
+beginning and ending with a ``"'' (double quote).
+The \s8DEC\s10 assembler conventions for flexible string quoting is
+not implemented.
+All ``C'' backslash conventions are observed; the backslash conventions
+peculiar to the \s-2PDP\-11\s+2 assembler are not observed.
+Strings are known by their value and their length; the assembler
+does not implicitly end strings with a null byte.
+.NH 2
+Operators
+.PP
+There are several single-character
+operators; see \(sc7.
+.NH 2
+Blanks
+.PP
+Blank and tab characters
+may be interspersed freely between tokens, but may
+not be used within tokens (except character constants).
+A blank or tab is required to separate adjacent
+identifiers or constants not otherwise separated.
+.NH 2
+Comments
+.NH 3
+Decadent Comments
+.PP
+The character ``\|#\|'' introduces a comment, which extends
+through the end of the line on which it appears.
+Comments starting in column 1,
+of the format ``\|# \fIexpression string\fP\|"
+are interpreted as an indication that the assembler is now assembling
+file \fIstring\fP at line \fIexpression\fP.
+Thus, one can use the C preprocessor on an assembly language source file,
+and use the \fI#include\fP and \fI#define\fP
+preprocessor directives.
+(Note that their may not be an assembler comment starting in column
+1 if the assembler source is given to the C preprocessor, as it will
+be intrepreted by the preprocessor in a way not intended.)
+Comments are otherwise ignored by the assembler.
+.NH 3
+C Style Comments
+.PP
+The assembler will recognize C style comments, introduced with
+the prologue \fB/*\fP and ending with the epilogue \fB*/\fP.
+C style comments may extend across multiple lines, and are the preferred
+comment style to use if one chooses to use the C preprocessor.
+.NH 1
+Segments and Location Counters
+.PP
+Assembled code and data fall into three segments: the text segment,
+the data segment, and the bss segment. The operating system makes
+some assumptions about the content of these segments; the assembler
+does not. Within the text and data segments there are a number of
+sub-segments, distinguished by number (``text 0'', ``text 1'', .\|.\|.
+``data 0'', ``data 1'', .\|.\|.\|).
+Currently there are four subsegments each in text and data.
+The subsegments are for programming convenience only. Before writing the
+output file, the assembler zero-pads each text subsegment to a multiple of four
+bytes and then concatenates the subsegments in order to form the text segment;
+an analogous operation is done for the data segment.
+Requesting that the loader define symbols and storage regions is the only
+action allowed by the assembler with respect to the bss segment.
+Assembly begins in ``text 0''.
+.PP
+Associated with each (sub)segment is an implicit location counter which
+begins at zero and is incremented by 1 for each byte assembled into the
+(sub)segment. There is no way to explicitly reference a location counter.
+Note that the location counters of subsegments other than ``text 0''
+and ``data 0'' behave peculiarly due to the concatenation used to form
+the text and data segments.
+.NH 1
+Statements
+.PP
+A source program is composed of a sequence of
+\fIstatements\fP.
+Statements are separated either by new-lines
+or by semicolons.
+There are two kinds of statements: null statements
+and keyword statements.
+Either kind of statement may be preceded by
+one or more labels.
+.NH 2
+Labels
+.NH 3
+Name (Global) Labels
+.PP
+A global label consists of a name followed
+by a colon ``\|:\|''.
+The effect of a name label is to assign the current
+value and type of the location counter
+to the name.
+An error is indicated in pass 1 if the
+name is already defined;
+an error is indicated in pass 2 if the
+value assigned changes the definition
+of the label.
+.PP
+A global label is referenced by its name.
+.PP
+Global labels beginning with a ``\|L\|''
+are discarded unless the \fB-L\fP option
+is in effect.
+.NH 3
+Numeric (Local) Labels
+.PP
+A numeric label consists of a digit \fI0\fP to \fI9\fP followed by a
+colon (``\|:\|'').
+Such a label serves to define temporary symbols of the form
+``\fIn\fPb'' and ``\fIn\fPf'',
+where \fIn\fP is the digit of the label.
+As in the case of name labels, a numeric label assigns
+the current value and type of the location counter
+to the temporary symbol.
+However, several numeric labels with the same digit
+may be used within the same assembly.
+References to symbols of the form
+``\fIn\fPb''
+refer to the first numeric label ``\fIn\|:\fP''
+\fIb\fP\|ackwards from the reference;
+``\fIn\fPf''
+symbols refer to the first numeric label ``\fIn\|:\fP''
+\fIf\fP\P\|orwards from the reference.
+Such numeric labels tend to conserve the inventive powers of
+the programmer.
+.NH 2
+Null statements
+.PP
+A null statement is an empty statement (which may, however,
+have labels).
+A null statement is ignored by the assembler.
+Common examples of null statements are empty
+lines or lines containing only a label.
+.NH 2
+Keyword statements
+.PP
+A keyword statement begins with one of the many predefined
+keywords of the assembler;
+the syntax of the remainder depends
+on the keyword.
+All instruction opcodes are keywords.
+The remaining keywords are assembler pseudo-operations,
+also called directives.
+The pseudo-operations are listed below with the syntax they require.
+.NH 1
+Expressions
+.PP
+An expression is a sequence of symbols representing a value.
+Its constituents are identifiers, constants,
+operators, and parentheses.
+Each expression has a type.
+.PP
+All operators in expressions are fundamentally binary in
+nature.
+Arithmetic is two's complement and has 32 bits of precision.
+There are four levels of precedence, listed here from
+lowest precedence level to highest:
+.IP (binary) 16
+\|+\|, -\|
+.IP (binary) 16
+\||\|, \|&\|, \|^\|, \|!\|
+.IP (binary) 16
+\|*\|, \|/\|, \|%\|, \|!\|
+.IP (unary) 16
+\|-\|, \|!\|
+.PP
+All operators of the same precedence are evaluated strictly left to right,
+except for evaluation order enforced by parenthesis.
+.NH 2
+Expression operators
+.PP
+The operators are:
+.IP + 16
+addition
+.IP \- 16
+subtraction
+.IP * 16
+multiplication
+.IP / 16
+division
+.IP %
+modulo
+.IP & 16
+bitwise and
+.IP \(bv 16
+bitwise or
+.IP ^ 16
+bitwise exclusive or
+.IP "> (or >>)" 16
+logical right shift
+.IP "< (or <<)" 16
+logical left shift
+.hc
+.IP ! 8
+\fIa\fR\|!\|\fIb\fR is \fIa \fBor \fR(\|\fBnot \fIb\fR\|);
+i.e., the \fBor\fR of the first operand and
+the one's complement of the second; most common use is
+as a unary operator.
+.PP
+Expressions may be grouped by use of parentheses ``\|(\|\|)\|''.
+.NH 2
+Types
+.PP
+The assembler deals with a number of types
+of expressions. Most types
+are attached to keywords and used to select the
+routine which treats that keyword. The types likely
+to be met explicitly are:
+.IP undefined 8
+.br
+Upon first encounter, each symbol is undefined.
+It may become undefined if it is assigned an undefined expression.
+It is an error to attempt to assemble an undefined
+expression in pass 2; in pass 1, it is not (except that
+certain keywords require operands which are not undefined).
+.IP "undefined external" 8
+.br
+A symbol which is declared \fB.globl\fR but not defined
+in the current assembly is an undefined
+external.
+If such a symbol is declared, the link editor \fIld\fR
+must be used to load the assembler's output with
+another routine that defines the undefined reference.
+.IP absolute 8
+.br
+An absolute symbol is defined ultimately from a constant.
+Its value is unaffected by any possible future applications
+of the link-editor to the output file.
+.IP text 8
+.br
+The value of a text symbol is measured
+with respect to the beginning of the text segment of the program.
+If the assembler output is link-edited, its text
+symbols may change in value
+since the program need
+not be the first in the link editor's output.
+Most text symbols are defined by appearing as labels.
+At the start of an assembly, the value of ``\|\fB.\fP\|'' is text 0.
+.IP data 8
+.br
+The value of a data symbol is measured
+with respect to the origin of the data segment of a program.
+Like text symbols, the value of a data symbol may change
+during a subsequent link-editor run since previously
+loaded programs may have data segments.
+After the first \fB.data\fR statement, the value of ``\|\fB.\fP\|''
+is data 0.
+.IP bss 8
+.br
+The value of a bss symbol is measured from
+the beginning of the bss segment of a program.
+Like text and data symbols, the value of a bss symbol
+may change during a subsequent link-editor
+run, since previously loaded programs may have bss segments.
+.IP "external absolute, text, data, or bss" 8
+.br
+symbols declared \fB.globl\fR
+but defined within an assembly as absolute, text, data, or bss
+symbols may be used exactly as if they were not
+declared \fB.globl\fR; however, their value and type are available
+to the link editor so that the program may be loaded with others
+that reference these symbols.
+.IP register 8
+.br
+The symbols
+.DS
+\fBr0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r10 r11 r12 r13 r14 r15\fP
+\fBap fp sp pc\fP
+.DE
+are predefined
+as register symbols.
+In addition, the % operator converts an absolute value to type register.
+.IP "other types" 8
+.br
+Each keyword known to the assembler has a type which
+is used to select the routine which processes
+the associated keyword statement.
+The behavior of such symbols
+when not used as keywords is the same as if they were absolute.
+.NH 2
+Type propagation in expressions
+.PP
+When operands are combined by expression operators,
+the result has a type which depends on the types
+of the operands and on the operator.
+The rules involved are complex to state but
+were intended to be sensible and predictable.
+For purposes of expression evaluation the
+important types are
+.DS
+undefined
+absolute
+text
+data
+bss
+undefined external
+other
+.DE
+The combination rules are then:
+If one of the operands
+is undefined, the result is undefined.
+If both operands are absolute, the result is absolute.
+If an absolute is combined with one of the ``other types''
+mentioned above,
+the result has the other type.
+An ``other type'' combined with an explicitly
+discussed type other than absolute
+it acts like an absolute.
+.PP
+Further rules applying to particular operators
+are:
+.IP +
+If one operand is text-, data-, or bss-segment
+relocatable, or is an undefined external,
+the result has the postulated type and the other operand
+must be absolute.
+.IP \-
+If the first operand is a relocatable
+text-, data-, or bss-segment symbol, the second operand
+may be absolute (in which case the result has the
+type of the first operand);
+or the second operand may have the same type
+as the first (in which case the result is absolute).
+If the first operand is external undefined, the second must be
+absolute.
+All other combinations are illegal.
+.PP
+.IP others
+.br
+It is illegal to apply these operators to any but absolute
+symbols.
+.NH 1
+Pseudo-operations (Directives)
+.PP
+The keywords listed below introduce
+influence the later operations of the assembler.
+The metanotation
+.DS
+[ stuff ] .\|.\|.
+.DE
+means that 0 or more instances of the given stuff may appear.
+The metatnotation
+.DS
+( stuff )\|*\|\|\fIn\fP\|
+.DE
+means that exactly \fIn\fP occurances of stuff must occur.
+.PP
+Boldface tokens are literals, italic words
+are substitutable.
+.PP
+The pseudo\-operations listed below are grouped into functional
+categories, and not alphabetically.
+.NH 2
+Interface to a Previous Pass
+.in +5m
+.NH 3
+\&.ABORT
+.PP
+As soon as the assembler sees this directive, it ignores all further
+input (but it does read to the end of file), and aborts the assembly.
+No files are created.
+It is anticipated that this would be used in a pipe interconnected
+version of a compiler, where the first major syntax error would
+cause the compiler to issue this directive, saving unnecessary
+work in assembling code that would have to be discarded anyway.
+.NH 3
+\&.file \fIstring\fP
+.PP
+This directive causes the assembler to think it is in file \fIstring\fP
+so error messages reflect the proper source file.
+.NH 3
+\&.line \fIexpression\fP
+.PP
+This directive causes the assembler to think it is on line \fIexpression\fP
+so error messages reflect the proper source file.
+.PP
+The only effect of assembling multiple files specified in the command string
+is to insert the
+\fIfile\fP and \fIline\fP directives, with the appropriate values,
+at the beginning of the source from each file.
+.NH 3
+Preprocessor Interface
+.DS
+\fI# expression string\fP
+\fI# expression\fP
+.DE
+.PP
+This is the only instance where a comment is meaningful to the assembler.
+The ``\|#\|''
+.ul 1
+must
+be in the first column.
+This meta comment causes the assembler
+to believe it is on line \fIexpression\fP.
+The second argument, if included, causes the assembler to believe it is in
+file \fIstring\fP, otherwise the current file name does not change.
+.in -5m
+.NH 2
+Location Counter Control
+.in +5m
+.NH 3
+\&\fB.align\fP \fIexpression\fP
+.PP
+The location counter is adjusted (by assembling bytes containing
+zeroes, if necessary) so that the \fIexpression\fP lowest bits
+become zero.
+Thus ``.align 2'' makes the location counter evenly divisible by 4.
+The expression must be defined, absolute, nonnegative,
+and less than 16.
+(Note that the subsegment concatenation convention
+and the current loader conventions may not preserve attempts at aligning
+to more than 2 low-order zero bits.)
+.NH 3
+Subsegment switching
+.DS
+ \fB.data\fP [ \fIexpression\fP ]
+ \fB.text\fP [ \fIexpression\fP ]
+.DE
+.PP
+These two pseudo-operations cause the
+assembler to begin assembling into the indicated text or data
+subsegment. If specified, the expression must be defined and absolute;
+an omitted expression is treated as zero.
+The effect of a \fB.data\fP directive is treated
+as a \fB.text\fP directive if the \fB\-R\fP assembly flag is set.
+Assembly starts in the text 0 subsegment.
+.NH 3
+\&\fB.org\fP \fIexpression\fP
+.PP
+The location counter is set equal to the value of the expression.
+The expression must be defined.
+The value of the expression must be greater than the current value
+of the location counter.
+.NH 3
+\&\fB.space\fP \fIexpression\fP
+.PP
+\&\fIexpression\fP bytes of zeroes are assembled.
+.in -5m
+.NH 2
+Initialized Data
+.in +5m
+.NH 3
+Expression Initialized Data
+.DS
+ \fB.byte \fIexpression \fR[ \fB, \fIexpression \fR] .\|.\|.
+ \fB.word \fIexpression \fR[ \fB, \fIexpression \fR] .\|.\|.
+ \fB.int \fIexpression \fR[ \fB, \fIexpression \fR] .\|.\|.
+ \fB.long \fIexpression \fR[ \fB, \fIexpression \fR] .\|.\|.
+
+ \fB.quad \fIexpression \fR[ \fB, \fIexpression \fR] .\|.\|.
+
+ \fB.float \fIexpression \fR[ \fB, \fIexpression \fR] .\|.\|.
+ \fB.double \fIexpression \fR[ \fB, \fIexpression \fR] .\|.\|.
+.DE
+.PP
+The \fIexpression\fP\|s in the comma-separated
+list are truncated to the indicated size
+(byte=8 bits,
+word=16,
+int=32,
+long=32,
+quad=64,
+float=32,
+double=64)
+and
+assembled in successive locations.
+The expressions must be absolute.
+The value assembled in bits 32-63 for \fB.double\fP is zero
+if the expression is not of type double.
+.PP
+Except for \fB.quad\fP, \fB.float\fP and \fB.double\fP,
+each expression may optionally be of the form
+.DS
+ \fIexpression\d\s-21\&\s+2\u\fP \fB:\fP \fIexpression\d\s-2\&2\s+2\u\fP.
+.DE
+In this case the value of \fIexpression\d\s-2\&2\s+2\u\fP
+is truncated to \fIexpression\d\s-2\&1\s+2\u\fP
+bits and assembled in the next \fIexpr\d\s-2\&1\s+2\u\fP-bit
+field which fits in
+the natural data size being assembled.
+Bits which are skipped because
+a field does not fit are made zero.
+Thus "\fB.byte\fP 123" is equivalent to
+"\fB.byte\fP 8:123" and "\fB.byte\fP 3:1,2:1,5:1"
+assembles two bytes, containing the values 9 and 1.
+.br
+\fBNB:\fP Since no \s-2VAX\s+2 compilers currently use bit fields,
+these bit field constructs are liable to disappear in the future.
+.NH 3
+String Initialized Data
+.DS
+ \fB.ascii\fP \fIstring\fP [ \fB,\fP \fIstring\fP ]
+ \fB.asciz\fP \fIstring\fP [ \fB,\fP \fIstring\fP ]
+.DE
+.PP
+Each \fIstring\fP in the list is assembled into successive locations,
+with the first letter in the string being placed
+into the first location, etc.
+The \fB.ascii\fP directive will not null pad the string;
+the \fB.asciz\fP directive will null pad the string.
+(Recall that strings are known by their length, and need not be terminated
+with a null, and that the C conventions for escaping are understood.)
+The \fB.ascii\fP directive is identical to:
+.DS
+\&\fB.byte\fP \fIstring\d\s-2\&0\s+2\u\fP\fB,\fP \fIstring\d\s-2\&1\s+2\u\fP\fB,\fP ...
+.DE
+.NH 3
+Zero Filled Data
+.DS
+\fB.space\fP \fIexpression\fP
+.DE
+.PP
+(See \(sc 8.2.4)
+\&\fIexpression\fP bytes of zeroes are assembled.
+\&\fIexpression\fP must be absolute.
+.NH 3
+Arbitrarily Filled Data
+.DS
+\fB.fill\fP
+\fIrep_expr\fP\fB, \fP
+\fIsize_expr\fP\fB, \fP
+\fIvalue_expr\fP\fR
+.DE
+.PP
+All three expressions must be absolute.
+\fIvalue_expr\fP,
+treated as an expression of size \fIsize_expr\fP bytes,
+is assembled and replicated \fIrep_expr\fP times.
+The effect is to advance the current location counter
+\fIrep_expr\fP \(** \fIsize_expr\fP bytes.
+\fIsize_expr\fP must be between 1 and 8.
+.in -5m
+.NH 2
+Symbol Definition
+.in +5m
+.NH 3
+General
+.in +5m
+.NH 4
+\&\fB.comm\fI name \fB, \fIexpression\fR
+.PP
+Provided the \fIname\fR is not defined elsewhere,
+its type is made ``undefined external'', and its value is \fIexpression\fR.
+In fact the \fIname\fR behaves
+in the current assembly just like an
+undefined external.
+However, the link editor \fIld\fR has been special-cased
+so that all external symbols which are not
+otherwise defined, and which have a non-zero
+value, are defined to lie in the bss
+segment, and enough space is left after the
+symbol to hold \fIexpression\fR
+bytes.
+.NH 4
+\&\fB.lcomm\fI name \fB, \fIexpression\fR
+.PP
+\fIexpression\fP bytes will be allocated in the bss segment and \fIname\fP
+assigned the location of the first byte, but the \fIname\fP is not declared
+as global and hence will be unknown to the link editor.
+.NH 4
+\&\fB.globl\fP \fIname\fP
+.PP
+This statement makes the \fIname\fR external.
+If it is otherwise defined (by \fB.set\fP or by
+appearance as a label)
+it acts within the assembly exactly as if
+the \fB.globl\fR statement were not given;
+however, the link editor may be used
+to combine this routine with other routines that refer
+to this symbol.
+.PP
+Conversely, if the given symbol is not defined
+within the current assembly, the link editor
+can combine the output of this assembly
+with that of others which define the symbol.
+The assembler makes all otherwise
+undefined symbols external.
+.NH 4
+\&\fB.set\fP \fIname\fP \fB,\fP \fIexpression\fP
+.PP
+The (\fIname\fP, \fIexpression\fP) pair is entered into the symbol table.
+Multiple \fB.set\fP statements with the same name are legal;
+the most recent value replaces all previous values.
+.in -5m
+.NH 3
+Debugger Support
+.in +5m
+.NH 4
+\&\fB.lsym\fP \fIname\fP \fB,\fP \fIexpression\fP
+.PP
+A unique and otherwise unreferenceable instance of the
+(\fIname\fP, \fIexpression\fP)
+pair is created in the symbol table.
+The Fortran 77 compiler uses this mechanism to pass local symbol definitions
+to the link editor and debugger.
+.NH 4
+Special Symbol Table entries
+.DS
+\&\fB.stab\fP (\fIexpr\d\s-2i\s+2\u \fB,\fR)\|*NCPS\| \fIexpr\d\s-2\&1\s+2\u\fB,\fP expr\d\s-2\&2\s+2\u\fB,\fP expr\d\s-2\&3\s+2\u\fB,\fP expr\d\s-2\&4\s+2\u\fR
+.in +5m
+\fR(normal \fBs\fPymbol \fBtab\fPle entry)\fR
+.in -5m
+\&\fB.stabs\fP \fIstring, expr\d\s-2\&1\s+2\u, expr\d\s-2\&2\s+2\u, expr\d\s-2\&3\s+2\u, expr\d\s-2\&4\s+2\u\fR
+.in +5m
+\fR(\fBstab s\fPtring)\fR
+.in -5m
+\&\fB.stabn\fP \fIexpr\d\s-2\&1\s+2\u\fB,\fP expr\d\s-2\&2\s+2\u\fB,\fP expr\d\s-2\&3\s+2\u\fB,\fP expr\d\s-2\&4\s+2\u\fR
+.in +5m
+\fR(\fBstab n\fPone)\fR
+.in -5m
+\&\fB.stabd\fP \fIexpr\d\s-2\&1\s+2\u\fB,\fP expr\d\s-2\&2\s+2\u\fB,\fP expr\d\s-2\&3\s+2\u\fR
+.in +5m
+\fR(\fBstab d\fPot)\fR
+.in -5m
+.DE
+.PP
+The \fIstab\fP directives place symbols in the symbol table for the symbolic
+debugger, \fIsdb\fP\s-2\u*\d\s+2.
+.FS
+.in +5
+.ti -5
+\s-2\u*\d\s+2Katseff, H.P. \fISdb: A Symbol Debugger\fP.
+Bell Laboratories, Holmdel,
+NJ. April 12, 1979.
+.br
+.ti -5
+\&Katseff, H.P. \fISymbol Table Format for Sdb\fP. File 39394,
+Bell Laboratores, Holmdel, NJ. March 14, 1979.
+.in -5
+.FE
+In the \fB.stab\fP directive,
+the first NCPS expressions are used for the
+symbol name, which may be zero.
+The \fB.stab\fP directive makes no sense if
+the assembler recognizes arbitrary length symbols;
+if so, the assembler complains.
+The \fIstring\fP in the \fB.stabs\fP
+directive more generally serves the same purpose as the NCPS expressions.
+If the symbol name is zero, the
+\&\fB.stabn\fP directive may be used instead.
+.PP
+The other expressions are stored in the name list structure in the symbol
+table and preserved by the loader for reference by \fIsdb\fP\fR;
+the value of the expressions are peculiar to formats required by \fIsdb\fP\fR.
+.in +5m
+.ti -5
+\&\fIexpr\d\s-2\&1\s+2\u\fP is used as a symbol table tag
+(nlist field \fIn_type\fP).
+.br
+.ti -5
+\&\fIexpr\d\s-2\&2\s+2\u\fP seems to always be zero
+(nlist field \fIn_other\fP).
+.br
+.ti -5
+\&\fIexpr\d\s-2\&3\s+2\u\fP is used for either the
+source line number, or for a nesting level
+(nlist field \fIn_desc\fP).
+.br
+.ti -5
+\fIexpr\d\s-2\&4\s+2\u\fR is used as tag specific information
+(nlist field \fIn_value\fP).
+In the
+case of the \fB.stabd\fP directive, this expression is nonexistant, and
+is taken to be the value of the location counter at the following instruction.
+Since there is no associated name for a \fB.stabd\fP directive, it can
+only be used in circumstances where the name is zero.
+The effect of a \fB.stabd\fP directive can be achieved by one of the other
+\&\fB.stab\fPx directives in the following manner:
+.in -5m
+.DS
+\& \fB.stabs\fP \fIstring\fB,\fP expr\d\s-2\&1\s+2\u\fB,\fP expr\d\s-2\&2\s+2\u\fB,\fP expr\d\s-2\&3\s+2\u\fB,\fP \fP LL\fIn\fP
+LL\fIn\fP\fB:\fP
+.DE
+The \fB.stabd\fP directive is prefered, because it does not clog the symbol
+table with labels used only for the stab symbol entries.
+.in -5m
+.in -5m
+.NH 1
+Machine instructions
+.PP
+The syntax of machine instruction statements accepted by \fIas\fP
+is generally similar to the syntax of \s8DEC MACRO\s10-32. There are
+differences, however.
+.NH 2
+Character set
+.PP
+\fIas\fP uses the character `$' instead of `#',
+and the character `*' instead of `@'. Opcodes and register names
+are spelled with lower-case rather than upper-case letters.
+.NH 2
+Lengths
+.PP
+Under certain circumstances, the following constructs are (optionallly)
+recognized by \&\fIas\fP to indicate the number of bytes to allocate
+for unresolved expressions used to specify displacement or indirect
+displacement addressing modes:
+.DS
+\&\fBB^\fP or \fBB\`\fP to indicate byte lengths (1 byte)
+\&\fBW^\fP or \fBW\`\fP to indicate word lengths (2 bytes)
+\&\fBL^\fP or \fBL\`\fP to indicate long word lengths (3 bytes)
+.DE
+One can also use lower case \fBb\fP, \fBw\fP or \fBl\fP instead of the upper
+case letters.
+There must be no space between the size specifier letter and the \fB^\fP or
+\&\fB\`\fP.
+The constructs \fBS^\fP and \fBG^\fP are not recognized
+by \fIas\fP as they are by the \s-2DEC\s+2 assembler.
+It is preferred to use the "\`" displacement specifier,
+so that the ``^'' is not
+misinterpreted as the \fBxor\fP operator.
+.PP
+Literal values (including floating-point literals used where the
+hardware expects a floating-point operand) are assembled as short
+literals if possible, hence not needing the \fBS^\fP \s-2DEC\s+2
+directive. If the value of the displacement is known exactly in the
+first pass \fIas\fP determines the length automatically, assembling it
+in the shortest possible way, ignoring (if present) the length
+expression. If the value of the displacement is not known in the first
+pass, \&\fI\fP will use the value of the displacement given by the
+optional length specifier, or will use the value specified by the
+\fB\-d\fP argument, or will default to 4 bytes.
+.NH 2
+CASE instructions
+.PP
+\fIas\fP considers the instructions \fBcaseb\fP, \fBcasel\fP, \fBcasew\fP
+to have three operands (namely: selector, base, limit).
+The displacements must be explicitly assembled using one
+or more \fB.word\fP statements.
+.NH 2
+Extended branch instructions
+.PP
+These opcodes (formed in general
+by substituting a ``j'' for the initial ``b''
+of the standard opcodes)
+take as branch destinations the name of a label in the current
+subsegment. If the destination is close enough then the corresponding
+``b'' instruction is assembled. Otherwise the assembler choses a sequence
+of one or more instructions which together have the same effect as if the
+``b'' instruction had a larger span. In general, \fIas\fP chooses the
+inverse branch followed by a \fBbrw\fP, but a \fBbrw\fP
+is sometimes pooled among several ``j'' instructions with the same
+destination.
+If the \fB\-J\fP assembler option is given,
+a \fBjmp\fP instruction is used instead of a \fBbrw\fP instruction
+for \fBALL\fP (!!) ``j'' instructions with distant destinations.
+This makes assembly of large (>32K bytes) assembly programs (inefficiently)
+possible.
+The current assembler does not try to use clever combinations of \fBbrb\fP,
+\fBbrw\fP and \fBjmp\fP instructions.
+The \fBjmp\fP instructions use PC relative addressing, with
+the length of the offset given by the ``\fB\-d\fP'' assembler
+option.
+.KS
+.DS
+.ft B
+.ta 1.0i 2.0i 3.0i
+jeql jeqlu jneq jnequ
+jgeq jgequ jgtr jgtru
+jleq jlequ jlss jlssu
+jbcc jbsc jbcs jbss
+jlbc jlbs
+jcc jcs
+jvc jvs
+jbc jbs
+jbr
+.DE
+.KE
+\fBjbr\fR turns into \fBbrb\fR
+if its target is close enough; else a \fBbrw\fP is used.
+.NH 1
+Diagnostics
+.PP
+Diagnostics are intended to be self explanatory and appear on
+the standard output.
+.NH 1
+Limits
+.DS
+.ta 2.0i
+Arbitrary Files to assemble
+Arbitrary Significant characters per name
+127 Characters per input line
+127 Characters per string
+Arbitrary Symbols
+4 Text segments
+4 Data segments
+.DE
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