Macro Assembler Directives
Processor Code Generation Directives .186 enables assembly of 80186 instructions .286 enables assembly of non privileged 80286 instructions .286C same as .286 .286P enables assembly of all 80286 instructions .287 enabled assembly of 80287 instructions .386 enabled assembly of non privileged 80386 instructions If used before .MODEL segments are defined as 32bits. Causes all segments to default to DWORD alignment. .386P enabled assembly of all 80386 instructions (see .386) .387 enabled assembly of 80387 instructions .8086 default, enables assembly of 8088/8086 instruction .8087 default, enables assembly of 8087 instructions These directives must precede the segment they are to effect. they cannot occur within a segment. Memory Model Directives .CODE [name] starts code segment; must follow .MODEL directive .CONST starts a constant data segment with name CONST; must follow .MODEL directive; placed in DGROUP .DATA starts a near data segment for initialized data with name _DATA; must follow .MODEL directive; placed in DGROUP .DATA? starts a near data segment for uninitialized data with name _BSS; must follow .MODEL directive; placed in DGROUP .FARDATA [name] not placed in any group .FARDATA? [name] not placed in any group .MODEL model defines memory model to be one of the following: SMALL, COMPACT, MEDIUM, LARGE or HUGE; must be used prior to any other segment directive .STACK [size] indicates start of stack segment named 'STACK' with size indicating number of bytes to reserve, default is 1k; placed in DGROUP Segment Definition, Segment Ordering and Linkage Directives .ALPHA orders segments alphabetically .SEQ orders segments sequentially (default) ASSUME sreg:name [,sreg:name...] selects default segment register to be used by the assembler, not the CPU, for addressing all symbols in the segment or group. Name must be associated with a SEGMENT or GROUP or set to "NOTHING" to indicate no segment register is to be associated. COMM def [,def...] defines variables that are both public and external (communal). Can be used in and include file to identify it to each source file without declaring it in each model as extern. Actually defines data once. Communal variables cannot be initialized, and are not guaranteed to be allocated contiguously since these are allocated by the linker. DOSSEG orders segments the same as DOS. This is Microsoft languages default order; causes paragph alignment END [name] marks end of source module and sets program start address (CS:IP) if 'name' is present name ENDP ends procedure 'name' name ENDS ends a segment or structure EXTRN name:type [,name:type...] defines one or more external symbols name GROUP seg[,seg] name LABEL [NEAR|FAR|PROC] defines an entry point; If PROC is specified, it's value depends on the current MODEL NAME pgmName ignored since MASM 5.0; used to set module name name PROC [NEAR|FAR] defines procedure; NEAR/FAR has .MODEL default PUBLIC name[,name...] makes symbol 'name' available to other modules name SEGMENT [align][combine][use]['class'] align = BYTE align on byte address (no alignment) = WORD align on even address = DWORD align on DWORD address = PARA align on next 16 byte paragraph = PAGE align on next 256 byte boundary combine = PUBLIC similar named segments are concatenated (CS) = STACK similar named segments are concatenated (SS) = COMMON similar named segment are overlapped = MEMORY similar names segments are concatenated = AT addr segment relative to absolute address = nothing segment is private and loaded independent use = USE16 segments will be 16 bits (if .386) = USE32 segments will be 32 bits (if .386) Data Allocation Directives ALIGN n aligns next variable or instruction on a boundary that is a multiple of "n". This can speed memory fetches on 16 and 32 bit CPU'S if aligned. New to MASM 5.0, previous versions used EVEN. Can result in NOP's added to code. [name] DB init[,init...] define byte [name] DD init[,init...] define double word (DWORD, 4 bytes) [name] DF init[,init...] define far word (FWORD, 386, 6 bytes) [name] DQ init[,init...] define quad word (QWORD, 8 bytes) [name] DT init[,init...] define temp word (TBYTE, 10 bytes) [name] DW init[,init...] define word (WORD, 2 bytes) count DUP (init[,init...]) duplicate 'init' 'count' times; DUP can be nested to 17 levels; DUP'ed initial values of (?) don't result in data in the object file but instead increment the next data addr name ENDS end of structure or segment EVEN same as align 2; Aligns data on even boundary ORG expr sets location counter to 'expr'; If 'expr' is '$' the code is ORG'ed at the current loc. name RECORD fld[,fld...] defines a byte or word variable consisting of bit fields; fields have the format: fieldname:width[=expr]; the sum of all widths must be <= 0 [name] STRUC <[init[,init]]> defines beginning of a structure; Values between <> are initializers; The '<>' symbols are required. Logical and Bit Oriented Directives expr1 AND expr2 returns nonzero if any set bit matches expr1 EQ expr2 returns (-1) for true or (0) for false expr1 GE expr2 returns (-1) for true or (0) for false expr1 LE expr2 returns (-1) for true or (0) for false expr1 LT expr2 returns (-1) for true or (0) for false MASK {fldname|record} returns bit mask for bits in record expr1 OR expr2 returns bitwise OR on expr1 and expr2 NOT expr returns 'expr' with all bits reversed expr SHL count returns expr shifted left count times expr SHR count returns expr shifted right count times WIDTH {fldname|record} returns width of field in bit record expr1 XOR expr2 returns bitwise XOR on expr1 and expr2 Other Operators and Directives [] index operator, same as addition .MSFLOAT encode floats in Microsoft Real Format .TYPE expr returns byte defining mode and scope of expr name EQU expr assigns expression to name. surround text with <> HIGH expr returns high byte of 'expr' INCLUDE filespec inserts code from 'filespec' into file INCLUDELIB filespec stores link library info in .OBJ file LENGTH var returns number of data objects in DUPed 'var' LOW expr returns low byte of 'expr' expr1 MOD expr2 return remainder of expr1/expr2 OFFSET expr returns offset of expr; When .MODEL is used the offset of a group relative segment refers to the end of the segment type PTR expr forces 'expr' to 'type' SEG expr returns segment of expression SHORT sets type of label to short, less than 128 bytes from start of next instruction SIZE var returns # of bytes allocated by DUP directive THIS type returns an operand of specified type whose offset and segment values are equal to the current location TYPE expr returns type of expression Program Listing and Documentation Directives .CREF restores listing of cross reference symbols .LALL include macro expansion in listings .LFCOND include false conditional blocks in listings .LIST starts listing of statements .SALL suppress listing of all macro expansions .SFCOND suppress false conditional blocks in listings .XALL start listing of macro expansion .XCREF [name[,name...]] suppress symbols in cross reference .XLIST suppress program listing COMMENT delimiter [text] PAGE [[len],wid] sets page length&width or ejects if no parms SUBTTL text defines program listing subtitle TITLE text defines program listing title Condition Assembly Directives ELSE else clause for conditional assembly block ENDIF terminates a conditional assembly block IFDEF name conditional assembly if name is defined Macro Definition Directives ENDM terminates a macro block EXITM exit macro expansion immediately IRP parm,parm in the statements enclosed by the IRP and ENDM will be repeated and replaced with the values of "arg" for each "arg" in the <>. IRPC parm, parm in the statements enclosed by the IRPC and ENDM will be repeated and replaced with the values of each char in the "string" for each character position in the string. "string" should be enclosed in <> if it contains spaces or other separators. LOCAL name[,name...] defines scope symbol as local to a macro name MACRO [parm[,parm...]] defines a macro and it's parameters PURGE name[,name] purges macros from memory REPT expr repeats all statements through ENDM statement for 'expr' times User Message Directives .ERR generates and error .ERR1 generates an error on PASS 1 .ERR2 generates an error on PASS 2 .ERRB generates an error if 'arg' is blank .ERRDEF name generates an error if 'name' is previously defined .ERRDIF[I] , .ERRE expr generates and error is 'expr' is false %OUT text displays 'text' to console Predefined Equates (available only if simplified segments are used) @curseg contains the current segment @filename current file name without extension @code contains the current code segment @codesize 0 for small & compact, 1 for large, medium & huge @datasize 0 for small & medium, 1 for compact & large, 2=huge @const contains segment of define by .CONST @data contains segment of define by .DATA @data? contains segment of define by .DATA? @fardata contains segment of define by .FARDATA @fardata? contains segment of define by .FARDATA? @stack contains segment of define by .STACK Most of these are only available if the simplified segment system is used. @curseg and @filename are available regardless. Radix Specifiers .RADIX expr sets radix [2..16] for numbers (dec. default) B binary data specifier Q octal data specifier O octal data specifier D decimal data specifier H hexadecimal data specifier