Microsoft Macro Assembler BNF Grammar

Article
03/13/2023

This page contains a BNF description of the MASM grammar. It's provided as a supplement to the reference and isn't guaranteed to be complete. Consult the reference for full information on keywords, parameters, operations, and so on.

To illustrate the use of the BNF, the following diagram shows the definition of the TYPEDEF directive, starting with the nonterminal typedefDir.

A chart showing the hierarchy of terminals and nonterminals that produce a typedefDir.

The entries under each horizontal brace are terminals, such as NEAR16, NEAR32, FAR16, and FAR32. Or, they're nonterminals such as qualifier, qualifiedType, distance, and protoSpec that can be further defined. Each italicized nonterminal in the typedefDir definition is also an entry in the BNF. Three vertical dots indicate a branching definition for a nonterminal that, for the sake of simplicity, this figure doesn't illustrate.

The BNF grammar allows recursive definitions. For example, the grammar uses qualifiedType as a possible definition for qualifiedType, which is also a component of the definition for qualifier. The "|" symbol specifies a choice between alternate expressions, for example endOfLine | comment. Double braces specify an optional parameter, for example ⟦ macroParmList ⟧. The brackets don't actually appear in the source code.

MASM Nonterminals

;;
endOfLine | comment

=Dir
id = immExpr ;;

addOp
+ | -

aExpr
term | aExpr && term

altId
id

alpha
Any upper or lowercase letter (A-Z) or one of these four characters: @ _ $ ?

arbitraryText
charList

asmInstruction
mnemonic ⟦ exprList ⟧

assumeDir
ASSUME assumeList ;;
| ASSUME NOTHING ;;

assumeList
assumeRegister | assumeList , assumeRegister

assumeReg
register : assumeVal

assumeRegister
assumeSegReg | assumeReg

assumeSegReg
segmentRegister : assumeSegVal

assumeSegVal
frameExpr | NOTHING | ERROR

assumeVal
qualifiedType | NOTHING | ERROR

bcdConst
⟦ sign ⟧ decNumber

binaryOp
== | != | >= | <= | > | < | &

bitDef
bitFieldId : bitFieldSize ⟦ = constExpr ⟧

bitDefList
bitDef | bitDefList , ⟦ ;; ⟧ bitDef

bitFieldId
id

bitFieldSize
constExpr

blockStatements
directiveList
| .CONTINUE ⟦ .IF cExpr ⟧
| .BREAK ⟦ .IF cExpr ⟧

bool
TRUE | FALSE

byteRegister
AL | AH | CL | CH | DL | DH | BL | BH | R8B | R9B | R10B | R11B | R12B | R13B | R14B | R15B

cExpr
aExpr | cExpr || aExpr

character
Any character with ordinal in the range 0–255 except linefeed (10).

charList
character | charList character

className
string

commDecl
⟦ nearfar ⟧ ⟦ langType ⟧ id : commType
⟦ : constExpr ⟧

commDir
COMM
commList ;;

comment
; text ;;

commentDir
COMMENT delimiter
text
text delimiter text ;;

commList
commDecl | commList , commDecl

commType
type | constExpr

constant
digits ⟦ radixOverride ⟧

constExpr
expr

contextDir
PUSHCONTEXT contextItemList ;;
| POPCONTEXT contextItemList ;;

contextItem
ASSUMES | RADIX | LISTING | CPU | ALL

contextItemList
contextItem | contextItemList , contextItem

controlBlock
whileBlock | repeatBlock

controlDir
controlIf | controlBlock

controlElseif
.ELSEIF cExpr ;;
directiveList
⟦ controlElseif ⟧

controlIf
.IF cExpr ;;
directiveList
⟦ controlElseif ⟧
⟦ .ELSE ;;
directiveList⟧
.ENDIF ;;

coprocessor
.8087 | .287 | .387 | .NO87

crefDir
crefOption ;;

crefOption
.CREF
| .XCREF ⟦ idList ⟧
| .NOCREF ⟦ idList ⟧

cxzExpr
expr
| ! expr
| expr == expr
| expr != expr

dataDecl
DB | DW | DD | DF | DQ | DT | dataType | typeId

dataDir
⟦ id ⟧ dataItem ;;

dataItem
dataDecl scalarInstList
| structTag structInstList
| typeId structInstList
| unionTag structInstList
| recordTag recordInstList

decdigit
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

decNumber
decdigit
| decNumber decdigit

delimiter
Any character except whiteSpaceCharacter

digits
decdigit
| digits decdigit
| digits hexdigit

directive
generalDir | segmentDef

directiveList
directive | directiveList directive

distance
nearfar | NEAR16 | NEAR32 | FAR16 | FAR32

e01
e01 orOp e02 | e02

e02
e02 AND e03 | e03

e03
NOT e04 | e04

e04
e04 relOp e05 | e05

e05
e05 addOp e06 | e06

e06
e06 mulOp e07 | e06 shiftOp e07 | e07

e07
e07 addOp e08 | e08

e08
HIGH e09
| LOW e09
| HIGHWORD e09
| LOWWORD e09
| e09

e10
e10 . e11
| e10 ⟦ expr ⟧
| e11

echoDir
ECHO arbitraryText ;;
%OUT arbitraryText ;;

elseifBlock
elseifStatement ;;
directiveList
⟦ elseifBlock ⟧

endDir
END ⟦ immExpr ⟧ ;;

endpDir
procId ENDP ;;

endsDir
id ENDS ;;

equDir
textMacroId EQU equType ;;

equType
immExpr | textLiteral

errorDir
errorOpt ;;

errorOpt
.ERR ⟦ textItem ⟧
| .ERRE constExpr ⟦ optText ⟧
| .ERRNZ constExpr ⟦ optText ⟧
| .ERRB textItem ⟦ optText ⟧
| .ERRNB textItem ⟦ optText ⟧
| .ERRDEF id ⟦ optText ⟧
| .ERRNDEF id ⟦ optText ⟧
| .ERRDIF textItem , textItem ⟦ optText ⟧
| .ERRDIFI textItem , textItem ⟦ optText ⟧
| .ERRIDN textItem , textItem ⟦ optText ⟧
| .ERRIDNI textItem , textItem ⟦ optText ⟧
| .ERR1 ⟦ textItem ⟧
| .ERR2 ⟦ textItem ⟧

exitDir
.EXIT ⟦ expr ⟧ ;;

exitmDir
: EXITM | EXITM textItem

exponent
E ⟦ sign ⟧ decNumber

expr
SHORT e05
| .TYPE e01
| OPATTR e01
| e01

exprList
expr | exprList , expr

externDef
⟦ langType ⟧ id ⟦ ( altId ) ⟧ : externType

externDir
externKey externList ;;

externKey
EXTRN | EXTERN | EXTERNDEF

externList
externDef | externList , ⟦ ;; ⟧ externDef

externType
ABS | qualifiedType

fieldAlign
constExpr

fieldInit
⟦ initValue ⟧ | structInstance

fieldInitList
fieldInit | fieldInitList , ⟦ ;; ⟧ fieldInit

fileChar
delimiter

fileCharList
fileChar | fileCharList fileChar

fileSpec
fileCharList | textLiteral

flagName
ZERO? | CARRY? | OVERFLOW? | SIGN? | PARITY?

floatNumber
⟦ sign ⟧ decNumber . ⟦ decNumber ⟧ ⟦ exponent ⟧
| digits R
| digits r

forcDir
FORC | IRPC

forDir
FOR | IRP

forParm
id ⟦ : forParmType ⟧

forParmType
REQ | = textLiteral

fpuRegister
ST expr

frameExpr
SEG id
| DGROUP : id
| segmentRegister : id
| id

gpRegister
AX | EAX | CX | ECX | DX | EDX | BX | EBX
| DI | EDI | SI | ESI | BP | EBP | SP | ESP
| R8W | R8D | R9W | R9D | R12D | R13W | R13D | R14W | R14D

groupDir
groupId GROUP segIdList

groupId
id

hexdigit
a | b | c | d | e | f
| A | B | C | D | E | F

id
alpha
| id alpha
| id decdigit
Maximum length is 247 characters.

idList
id | idList , id

ifDir
ifStatement ;;
directiveList
⟦ elseifBlock ⟧
⟦ ELSE ;;
directiveList ⟧ ;;

immExpr
expr

includeDir
INCLUDE fileSpec ;;

includeLibDir
INCLUDELIB fileSpec ;;

inSegDir
⟦ labelDef ⟧ inSegmentDir

inSegDirList
inSegDir | inSegDirList inSegDir

instruction
⟦ instrPrefix ⟧ asmInstruction

invokeArg
register :: register
| expr
| ADDR expr

invokeDir
INVOKE expr ⟦ , ⟦ ;; ⟧ invokeList ⟧ ;;

invokeList
invokeArg | invokeList , ⟦ ;; ⟧ invokeArg

keyword
Any reserved word.

keywordList
keyword | keyword keywordList

labelDef
id : | id :: | @@:

labelDir
id LABEL qualifiedType ;;

listDir
listOption ;;

localDef
LOCAL idList ;;

localDir
LOCAL parmList ;;

localDirList
localDir | localDirList localDir

localList
localDef | localList localDef

macroArgList
macroArg | macroArgList , macroArg

macroBody
⟦ localList ⟧ macroStmtList

macroCall
id macroArgList ;;
| id ( macroArgList )

macroDir
id MACRO ⟦ macroParmList ⟧ ;;
macroBody
ENDM ;;

macroFor
forDir forParm , < macroArgList > ;;
macroBody
ENDM ;;

macroForc
forcDir id , textLiteral ;;
macroBody
ENDM ;;

macroFuncId
id

macroId
macroProcId | macroFuncId

macroIdList
macroId | macroIdList , macroId

macroLabel
id

macroParm
id ⟦ : parmType ⟧

macroParmList
macroParm | macroParmList , ⟦ ;; ⟧ macroParm

macroProcId
id

macroRepeat
repeatDir constExpr ;;
macroBody
ENDM ;;

macroStmt
directive
| exitmDir
| : macroLabel
| GOTO macroLabel

macroStmtList
macroStmt ;;
| macroStmtList macroStmt ;;

macroWhile
WHILE constExpr ;;
macroBody
ENDM ;;

mapType
ALL | NONE | NOTPUBLIC

mnemonic
Instruction name.

modelDir
.MODEL memOption ⟦ , modelOptlist ⟧ ;;

modelOpt
langType | stackOption

modelOptlist
modelOpt | modelOptlist , modelOpt

module
⟦ directiveList ⟧ endDir

mulOp
* | / | MOD

nameDir
NAME id ;;

nearfar
NEAR | FAR

nestedStruct
structHdr ⟦ id ⟧ ;;
structBody
ENDS ;;

offsetDir
offsetDirType ;;

offsetDirType
EVEN
| ORG immExpr
| ALIGN ⟦ constExpr ⟧

offsetType
GROUP | SEGMENT | FLAT

oldRecordFieldList
⟦ constExpr ⟧ | oldRecordFieldList , ⟦ constExpr ⟧

optionDir
OPTION optionList ;;

optionList
optionItem | optionList , ⟦ ;; ⟧ optionItem

optText
, textItem

orOp
OR | XOR

oVisibility
PUBLIC | PRIVATE | EXPORT

pageDir
PAGE ⟦ pageExpr ⟧ ;;

pageExpr
+ | ⟦ pageLength ⟧ ⟦ , pageWidth ⟧

pageLength
constExpr

pageWidth
constExpr

parm
parmId ⟦ : qualifiedType ⟧
| parmId ⟦ constExpr ⟧ ⟦ : qualifiedType ⟧

parmId
id

parmList
parm | parmList , ⟦ ;; ⟧ parm

parmType
REQ | = textLiteral | VARARG

pOptions
⟦ distance ⟧ ⟦ langType ⟧ ⟦ oVisibility ⟧

primary
expr binaryOp expr | flagName | expr

procDir
procId PROC ⟦ pOptions ⟧ ⟦ < macroArgList > ⟧
⟦ usesRegs ⟧ ⟦ procParmList ⟧

processor
| .386 | .386p | .486 | .486P
| .586 | .586P | .686 | .686P | .387

processorDir
processor ;;
| coprocessor ;;

procId
id

procItem
instrPrefix | dataDir | labelDir | offsetDir | generalDir

procParmList
⟦ , ⟦ ;; ⟧ parmList ⟧
⟦ , ⟦ ;; ⟧ parmId :VARARG ⟧

protoArg
⟦ id ⟧ : qualifiedType

protoArgList
⟦ , ⟦ ;; ⟧ protoList ⟧
⟦ , ⟦ ;; ⟧ ⟦ id ⟧ :VARARG ⟧

protoList
protoArg
| protoList , ⟦ ;; ⟧ protoArg

protoSpec
⟦ distance ⟧ ⟦ langType ⟧ ⟦ protoArgList ⟧
| typeId

protoTypeDir
id PROTO protoSpec

pubDef
⟦ langType ⟧ id

publicDir
PUBLIC pubList ;;

pubList
pubDef | pubList , ⟦ ;; ⟧ pubDef

purgeDir
PURGE macroIdList

qualifiedType
type
| ⟦ distance ⟧ PTR ⟦ qualifiedType ⟧

qualifier
qualifiedType | PROTO protoSpec

quote
" | '

qwordRegister
RAX | RCX | RDX | RBX | RSP | RBP | RSI | RDI
| R8 | R9 | R10 | R11 | R12 | R13 | R14 | R15

radixDir
.RADIX constExpr ;;

radixOverride
h | o | q | t | y
| H | O | Q | T | Y

recordConst
recordTag { oldRecordFieldList }
| recordTag < oldRecordFieldList >

recordDir
recordTag RECORD bitDefList ;;

recordFieldList
⟦ constExpr ⟧ | recordFieldList , ⟦ ;; ⟧ ⟦ constExpr ⟧

recordInstance
{ ⟦ ;; ⟧ recordFieldList ⟦ ;; ⟧ }
| < oldRecordFieldList >
| constExpr DUP ( recordInstance )

recordInstList
recordInstance | recordInstList , ⟦ ;; ⟧ recordInstance

recordTag
id

regList
register | regList register

relOp
EQ | NE | LT | LE | GT | GE

repeatBlock
.REPEAT ;;
blockStatements ;; untilDir ;;

repeatDir
REPEAT | REPT

scalarInstList
initValue
| scalarInstList , ⟦ ;; ⟧ initValue

segAlign
BYTE | WORD | DWORD | PARA | PAGE

segId
id

segIdList
segId
| segIdList , segId

segmentDef
segmentDir ⟦ inSegDirList ⟧ endsDir | simpleSegDir ⟦ inSegDirList ⟧ ⟦ endsDir ⟧

segmentDir
segId SEGMENT ⟦ segOptionList ⟧ ;;

segmentRegister
CS | DS | ES | FS | GS | SS

segOption
segAlign
| segRO
| segAttrib
| segSize
| className

segOptionList
segOption | segOptionList segOption

segOrderDir
.ALPHA | .SEQ | .DOSSEG | DOSSEG

segRO
READONLY

segSize
USE16 | USE32 | FLAT

shiftOp
SHR | SHL

sign
+ | -

simdRegister
MM0 | MM1 | MM2 | MM3 | MM4 | MM5 | MM6 | MM7
| xmmRegister
| YMM0 | YMM1 | YMM2 | YMM3 | YMM4 | YMM5 | YMM6 | YMM7
| YMM8 | YMM9 | YMM10 | YMM11 | YMM12 | YMM13 | YMM14 | YMM15

simpleExpr
( cExpr ) | primary

simpleSegDir
segDir ;;

sizeArg
id | type | e10

specialChars
: | . | [ | ] | ( | ) | < | > | { | }
| + | - | / | * | & | % | !
| ' | \ | = | ; | , | "
| whiteSpaceCharacter
| endOfLine

specialRegister
CR0 | CR2 | CR3
| DR0 | DR1 | DR2 | DR3 | DR6 | DR7
| TR3 | TR4 | TR5 | TR6 | TR7

stackOption
NEARSTACK | FARSTACK

startupDir
.STARTUP ;;

stext
stringChar | stext stringChar

string
quote ⟦ stext ⟧ quote

stringChar
quote quote | Any character except quote.

structBody
structItem ;;
| structBody structItem ;;

structDir
structTag structHdr ⟦ fieldAlign ⟧
⟦ , NONUNIQUE ⟧ ;;
structBody
structTag ENDS ;;

structHdr
STRUC | STRUCT | UNION

structInstance
< ⟦ fieldInitList ⟧ >
| { ⟦ ;; ⟧ ⟦ fieldInitList ⟧ ⟦ ;; ⟧ }
| constExpr DUP ( structInstList )

structInstList
structInstance | structInstList , ⟦ ;; ⟧ structInstance

structItem
dataDir
| generalDir
| offsetDir
| nestedStruct

structTag
id

term
simpleExpr | ! simpleExpr

text
textLiteral | text character | ! character text | character | ! character

textDir
id textMacroDir ;;

textItem
textLiteral | textMacroId | % constExpr

textLen
constExpr

textList
textItem | textList , ⟦ ;; ⟧ textItem

textLiteral
< text > ;;

textMacroDir
CATSTR ⟦ textList ⟧
| TEXTEQU ⟦ textList ⟧
| SIZESTR textItem
| SUBSTR textItem , textStart ⟦ , textLen ⟧
| INSTR ⟦ textStart , ⟧ textItem , textItem

textMacroId
id

textStart
constExpr

titleDir
titleType arbitraryText ;;

titleType
TITLE | SUBTITLE | SUBTTL

typedefDir
typeId TYPEDEF qualifier

typeId
id

unionTag
id

untilDir
.UNTIL cExpr ;;
.UNTILCXZ ⟦ cxzExpr ⟧ ;;

usesRegs
USES regList

whileBlock
.WHILE cExpr ;;
blockStatements ;;
.ENDW

whiteSpaceCharacter
ASCII 8, 9, 11–13, 26, 32

xmmRegister
XMM0 | XMM1 | XMM2 | XMM3 | XMM4 | XMM5 | XMM6 | XMM7
| XMM8 | XMM9 | XMM10 | XMM11 | XMM12 | XMM13 | XMM14 | XMM15

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