.BP .SN 11 .S1 "EM ASSEMBLY LANGUAGE" We use two representations for assembly language programs, one is in ASCII and the other is the compact assembly language. The latter needs less space than the first for the same program and therefore allows faster processing. Our only program accepting ASCII assembly language converts it to the compact form. All other programs expect compact assembly input. The first part of the chapter describes the ASCII assembly language and its semantics. The second part describes the syntax of the compact assembly language. The last part lists the EM instructions with the type of arguments allowed and an indication of the function. Appendix A gives a detailed description of the effect of all instructions in the form of a Pascal program. .S2 "ASCII assembly language" An assembly language program consists of a series of lines, each line may be blank, contain one (pseudo)instruction or contain one label. Input to the assembler is in lower case. Upper case is used in this document merely to distinguish keywords from the surrounding prose. Comment is allowed at the end of each line and starts with a semicolon ";". This kind of comment does not exist in the compact form. .A Labels must be placed all by themselves on a line and start in column 1. There are two kinds of labels, instruction and data labels. Instruction labels are unsigned positive integers. The scope of an instruction label is its procedure. .A The pseudoinstructions CON, ROM and BSS may be preceded by a line containing a 1-8 character data label, the first character of which is a letter, period or underscore. The period may only be followed by digits, the others may be followed by letters, digits and underscores. The use of the character "." followed by a constant, which must be in the range 1 to 32767 (e.g. ".40") is recommended for compiler generated programs. These labels are considered as a special case and handled more efficiently in compact assembly language (see below). Note that a data label on its own or two consecutive labels are not allowed. .P Each statement may contain an instruction mnemonic or pseudoinstruction. These must begin in column 2 or later (not column 1) and must be followed by a space, tab, semicolon or LF. Everything on the line following a semicolon is taken as a comment. .P Each input file contains one module. A module may contain many procedures, which may be nested. A procedure consists of a PRO statement, a (possibly empty) collection of instructions and pseudoinstructions and finally an END statement. Pseudoinstructions are also allowed between procedures. They do not belong to a specific procedure. .P All constants in EM are interpreted in the decimal base. The ASCII assembly language accepts constant expressions wherever constants are allowed. The operators recognized are: +, -, *, % and / with the usual precedence order. Use of the parentheses ( and ) to alter the precedence order is allowed. .S3 "Instruction arguments" Unlike many other assembly languages, the EM assembly language requires all arguments of normal and pseudoinstructions to be either a constant or an identifier, but not a combination of these two. There is one exception to this rule: when a data label is used for initialization or as an instruction argument, expressions of the form 'label+constant' and 'label-constant' are allowed. This makes it possible to address, for example, the third word of a ten word BSS block directly. Thus LOE LABEL+4 is permitted and so is CON LABEL+3. The resulting address is must be in the same fragment as the label. It is not allowed to add or subtract from instruction labels or procedure identifiers, which certainly is not a severe restriction and greatly aids optimization. .P Instruction arguments can be constants, data labels, data labels offsetted by a constant, instruction labels and procedure identifiers. The range of integers allowed depends on the instruction. Most instructions allow only integers (signed or unsigned) that fit in a word. Arguments used as offsets to pointers should fit in a pointer-sized integer. Finally, arguments to LDC should fit in a double-word integer. .P Several instructions have two possible forms: with an explicit argument and with an implicit argument on top of the stack. The size of the implicit argument is the wordsize. The implicit argument is always popped before all other operands. For example: 'CMI 4' specifies that two four-byte signed integers on top of the stack are to be compared. \&'CMI' without an argument expects a wordsized integer on top of the stack that specifies the size of the integers to be compared. Thus the following two sequences are equivalent: .N 2 .TS center, tab(:) ; l r 30 l r. LDL:-10:LDL:-10 LDL:-14:LDL:-14 ::LOC:4 CMI:4:CMI: ZEQ:*1:ZEQ:*1 .TE 2 Section 11.1.6 shows the arguments allowed for each instruction. .S3 "Pseudoinstruction arguments" Pseudoinstruction arguments can be divided in two classes: Initializers and others. The following initializers are allowed: signed integer constants, unsigned integer constants, floating-point constants, strings, data labels, data labels offsetted by a constant, instruction labels and procedure identifiers. .P Constant initializers in BSS, HOL, CON and ROM pseudoinstructions can be followed by a letter I, U or F. This indicator specifies the type of the initializer: Integer, Unsigned or Float. If no indicator is present I is assumed. The size of the initializer is the wordsize unless the indicator is followed by an integer specifying the initializer's size. This integer is governed by the same restrictions as for transfer of objects to/from memory. As in instruction arguments, initializers include expressions of the form: \&"LABEL+offset" and "LABEL-offset". The offset must be an unsigned decimal constant. The 'IUF' indicators cannot be used in the offsets. .P Data labels are referred to by their name. .P Strings are surrounded by double quotes ("). Semicolon's in string do not indicate the start of comment. In the ASCII representation the escape character \e (backslash) alters the meaning of subsequent character(s). This feature allows inclusion of zeroes, graphic characters and the double quote in the string. The following escape sequences exist: .DS .TS center, tab(:); l l l. newline:NL\|(LF):\en horizontal tab:HT:\et backspace:BS:\eb carriage return:CR:\er form feed:FF:\ef backslash:\e:\e\e double quote:":\e" bit pattern:\fBddd\fP:\e\fBddd\fP .TE .DE The escape \fBddd\fP consists of the backslash followed by 1, 2, or 3 octal digits specifing the value of the desired character. If the character following a backslash is not one of those specified, the backslash is ignored. Example: CON "hello\e012\e0". Each string element initializes a single byte. The ASCII character set is used to map characters onto values. .P Instruction labels are referred to as *1, *2, etc. in both branch instructions and as initializers. .P The notation $procname means the identifier for the procedure with the specified name. This identifier has the size of a pointer. .S3 Notation First, the notation used for the arguments, classes of instructions and pseudoinstructions. .IS 2 .TS tab(:); l l l. :\&=:integer constant (current range -2**31..2**31-1) :\&=:data label :\&=: or or + or - :\&=:integer constant, unsigned constant, floating-point constant :\&=:string constant (surrounded by double quotes), :\&=:instruction label ::'*' followed by an integer in the range 0..32767. :\&=:procedure number ('$' followed by a procedure name) :\&=:, , or . :\&=: or <...>*:\&=:zero or more of <...> <...>+:\&=:one or more of <...> [...]:\&=:optional ... .TE .IE .S3 "Pseudoinstructions" .S4 Storage declaration Initialized global data is allocated by the pseudoinstruction CON, which needs at least one argument. Each argument is used to allocate and initialize a number of consequtive bytes in data memory. The number of bytes to be allocated and the alignment depend on the type of the argument. For each argument, an integral number of words, determined by the argument type, is allocated and initialized. .P The pseudoinstruction ROM is the same as CON, except that it guarantees that the initialized words will not change during the execution of the program. This information allows optimizers to do certain calculations such as array indexing and subrange checking at compile time instead of at run time. .P The pseudoinstruction BSS allocates uninitialized global data or large blocks of data initialized by the same value. The first argument to this pseudo is the number of bytes required, which must be a multiple of the wordsize. The other arguments specify the value used for initialization and whether the initialization is only for convenience or a strict necessity. The pseudoinstruction HOL is similar to BSS in that it requests an (un)initialized global data block. Addressing of a HOL block, however, is quasi absolute. The first byte is addressed by 0, the second byte by 1 etc. in assembly language. The assembler/loader adds the base address of the HOL block to these numbers to obtain the absolute address in the machine language. .P The scope of a HOL block starts at the HOL pseudo and ends at the next HOL pseudo or at the end of a module whatever comes first. Each instruction falls in the scope of at most one HOL block, the current HOL block. It is not allowed to have more than one HOL block per procedure. .P The alignment restrictions are enforced by the pseudoinstructions. All initializers are aligned on a multiple of their size or the wordsize whichever is smaller. Strings form an exception, they are to be seen as a sequence of initializers each for one byte, i.e. strings are not padded with zero bytes. Switching to another type of fragment or placing a label forces word-alignment. There are three types of fragments in global data space: CON, ROM and BSS/HOL. .N 2 .IS 2 .PS - 4 .PT "BSS ,," Reserve bytes. is the value used to initialize the area. must be a multiple of the size of . is 0 if the initialization is not strictly necessary, 1 if it is. .PT "HOL ,," Idem, but all following absolute global data references will refer to this block. Only one HOL is allowed per procedure, it has to be placed before the first instruction. .PT "CON +" Assemble global data words initialized with the constants. .PT "ROM +" Idem, but the initialized data will never be changed by the program. .PE .IE .S4 Partitioning Two pseudoinstructions partition the input into procedures: .IS 2 .PS - 4 .PT "PRO [,]" Start of procedure. is the procedure name. is the number of bytes for locals. The number of bytes for locals must be specified in the PRO or END pseudoinstruction. When specified in both, they must be identical. .PT "END []" End of Procedure. is the number of bytes for locals. The number of bytes for locals must be specified in either the PRO or END pseudoinstruction or both. .PE .IE .S4 Visibility Names of data and procedures in an EM module can either be internal or external. External names are known outside the module and are used to link several pieces of a program. Internal names are not known outside the modules they are used in. Other modules will not 'see' an internal name. .A To reduce the number of passes needed, it must be known at the first occurrence whether a name is internal or external. If the first occurrence of a name is in a definition, the name is considered to be internal. If the first occurrence of a name is a reference, the name is considered to be external. If the first occurrence is in one of the following pseudoinstructions, the effect of the pseudo has precedence. .IS 2 .PS - 4 .PT "EXA " External name. is known, possibly defined, outside this module. Note that may be defined in the same module. .PT "EXP " External procedure identifier. Note that may be defined in the same module. .PT "INA " Internal name. is internal to this module and must be defined in this module. .PT "INP " Internal procedure. is internal to this module and must be defined in this module. .PE .IE .S4 Miscellaneous Two other pseudoinstructions provide miscellaneous features: .IS 2 .PS - 4 .PT "EXC ," Two blocks of instructions preceding this one are interchanged before being processed. gives the number of lines of the first block. gives the number of lines of the second one. Blank and pure comment lines do not count. .PT "MES [,]*" A special type of comment. Used by compilers to communicate with the optimizer, assembler, etc. as follows: .VS 1 0 .PS - 4 .PT "MES 0" An error has occurred, stop further processing. .PT "MES 1" Suppress optimization. .PT "MES 2,," Use wordsize and pointer size . .PT "MES 3,,,," Indicates that a local variable is never referenced indirectly. Used to indicate that a register may be used for a specific variable. is offset in bytes from AB if positive and offset from LB if negative. gives the size of the variable. indicates the class of the variable. The following values are currently recognized: .PS .PT 0 The variable can be used for anything. .PT 1 The variable is used as a loopindex. .PT 2 The variable is used as a pointer. .PT 3 The variable is used as a floating point number. .PE 0 gives the priority of the variable, higher numbers indicate better candidates. .PT "MES 4,," Number of source lines in file (for profiler). .PT "MES 5" Floating point used. .PT "MES 6,*" Comment. Used to provide comments in compact assembly language. .PT "MES 7,....." Reserved. .PT "MES 8,[,]..." Library module. Indicates that the module may only be loaded if it is useful, that is, if it can satisfy any unresolved references during the loading process. May not be preceded by any other pseudo, except MES's. .PT "MES 9," Guarantees that no more than bytes of parameters are accessed, either directly or indirectly. .PE 1 .VS 1 1 Each backend is free to skip irrelevant MES pseudos. .PE .IE .S2 "The Compact Assembly Language" The assembler accepts input in a highly encoded form. This form is intended to reduce the amount of file transport between the front ends, optimizers and back ends, and also reduces the amount of storage required for storing libraries. Libraries are stored as archived compact assembly language, not machine language. .P When beginning to read the input, the assembler is in neutral state, and expects either a label or an instruction (including the pseudoinstructions). The meaning of the next byte(s) when in neutral state is as follows, where b1, b2 etc. represent the succeeding bytes. .N 1 .DS .TS tab(:) ; rw17 4 l. 0:Reserved for future use 1-129:Machine instructions, see Appendix A, alphabetical list 130-149:Reserved for future use 150-161:BSS,CON,END,EXA,EXC,EXP,HOL,INA,INP,MES,PRO,ROM 162-179:Reserved for future pseudoinstructions 180-239:Instruction labels 0 - 59 (180 is local label 0 etc.) 240-244:See the Common Table below 245-255:Not used .TE 1 .DE 0 After a label, the assembler is back in neutral state; it can immediately accept another label or an instruction in the next byte. No linefeeds are used to separate lines. .P If an opcode expects no arguments, the assembler is back in neutral state after reading the one byte containing the instruction number. If it has one or more arguments (only pseudos have more than 1), the arguments follow directly, encoded as follows: .N 1 .IS 2 .TS tab(:); r l. 0-239:Offsets from -120 to 119 240-255:See the Common Table below .TE 1 Absence of an optional argument is indicated by a special byte. .IE 2 .CS Common Table for Neutral State and Arguments .CE .TS tab(:); c c s c l8 l l8 l. class:bytes:description :240:b1:Instruction label b1 (Not used for branches) :241:b1 b2:16 bit instruction label (256*b2 + b1) :242:b1:Global label .0-.255, with b1 being the label :243:b1 b2:Global label .0-.32767 :::with 256*b2+b1 being the label :244::Global symbol not of the form .nnn :245:b1 b2:16 bit constant :246:b1 b2 b3 b4:32 bit constant :247:b1 .. b8:64 bit constant :248::Global label + (possibly negative) constant :249::Procedure name (not including $) :250::String used in CON or ROM (no quotes-no escapes) :251::Integer constant, size bytes :252::Unsigned constant, size bytes :253::Floating constant, size bytes :254::unused :255::Delimiter for argument lists or :::indicates absence of optional argument .TE 1 .P The bytes specifying the value of a 16, 32 or 64 bit constant are presented in two's complement notation, with the least significant byte first. For example: the value of a 32 bit constant is ((s4*256+b3)*256+b2)*256+b1, where s4 is b4-256 if b4 is greater than 128 else s4 takes the value of b4. A consists of a inmediatly followed by a sequence of bytes with length . .P .ne 8 The pseudoinstructions fall into several categories, depending on their arguments: .N 1 .DS Group 1 -- EXC, BSS, HOL have a known number of arguments Group 2 -- EXA, EXP, INA, INP have a string as argument Group 3 -- CON, MES, ROM have a variable number of various things Group 4 -- END, PRO have a trailing optional argument. .DE 1 Groups 1 and 2 use the encoding described above. Group 3 also uses the encoding listed above, with an byte after the last argument to indicate the end of the list. Group 4 uses an byte if the trailing argument is not present. .N 2 .IS 2 .TS tab(|); l s l l s s l 2 lw(46) l. Example ASCII|Example compact (LOC = 69, BRA = 18 here): 2||182 1||181 LOC|10|69 130 LOC|-10|69 110 LOC|300|69 245 44 1 BRA|*19|18 139 300||241 44 1 .3||242 3 CON|4,9,*2,$foo|151 124 129 240 2 249 123 102 111 111 255 CON|.35|151 242 35 255 .TE 0 .IE 0 .BP .S2 "Assembly language instruction list" .P For each instruction in the list the range of argument values in the assembly language is given. The column headed \fIassem\fP contains the mnemonics defined in 11.1.3. The following column specifies restrictions of the argument value. Addresses have to obey the restrictions mentioned in chapter 2. The classes of arguments are indicated by letters: .ds b \fBb\fP .ds c \fBc\fP .ds d \fBd\fP .ds g \fBg\fP .ds f \fBf\fP .ds l \fBl\fP .ds n \fBn\fP .ds w \fBw\fP .ds p \fBp\fP .ds r \fBr\fP .ds s \fBs\fP .ds z \fBz\fP .ds o \fBo\fP .ds - \fB-\fP .N 1 .TS tab(:); c s l l l l 15 l l. \fIassem\fP:constraints:rationale \&\*c:cst:fits word:constant \&\*d:cst:fits double word:constant \&\*l:cst::local offset \&\*g:arg:>= 0:global offset \&\*f:cst::fragment offset \&\*n:cst:>= 0:counter \&\*s:cst:>0 , word multiple:object size \&\*z:cst:>= 0 , zero or word multiple:object size \&\*o:cst:>= 0 , word multiple or fraction:object size \&\*w:cst:> 0 , word multiple:object size * \&\*p:pro::pro identifier \&\*b:ilb:>= 0:label number \&\*r:cst:0,1,2:register number \&\*-:::no argument .TE 1 .P The * at the rationale for \*w indicates that the argument can either be given as argument or on top of the stack. If the argument is omitted, the argument is fetched from the stack; it is assumed to be a wordsized unsigned integer. Instructions that check for undefined integer or floating-point values and underflow or overflow are indicated below by (*). .N 1 .DS B GROUP 1 - LOAD LOC \*c : Load constant (i.e. push one word onto the stack) LDC \*d : Load double constant ( push two words ) LOL \*l : Load word at \*l-th local (\*l<0) or parameter (\*l>=0) LOE \*g : Load external word \*g LIL \*l : Load word pointed to by \*l-th local or parameter LOF \*f : Load offsetted (top of stack + \*f yield address) LAL \*l : Load address of local or parameter LAE \*g : Load address of external LXL \*n : Load lexical (address of LB \*n static levels back) LXA \*n : Load lexical (address of AB \*n static levels back) LOI \*o : Load indirect \*o bytes (address is popped from the stack) LOS \*w : Load indirect, \*w-byte integer on top of stack gives object size LDL \*l : Load double local or parameter (two consecutive words are stacked) LDE \*g : Load double external (two consecutive externals are stacked) LDF \*f : Load double offsetted (top of stack + \*f yield address) LPI \*p : Load procedure identifier GROUP 2 - STORE STL \*l : Store local or parameter STE \*g : Store external SIL \*l : Store into word pointed to by \*l-th local or parameter STF \*f : Store offsetted STI \*o : Store indirect \*o bytes (pop address, then data) STS \*w : Store indirect, \*w-byte integer on top of stack gives object size SDL \*l : Store double local or parameter SDE \*g : Store double external SDF \*f : Store double offsetted GROUP 3 - INTEGER ARITHMETIC ADI \*w : Addition (*) SBI \*w : Subtraction (*) MLI \*w : Multiplication (*) DVI \*w : Division (*) RMI \*w : Remainder (*) NGI \*w : Negate (two's complement) (*) SLI \*w : Shift left (*) SRI \*w : Shift right (*) GROUP 4 - UNSIGNED ARITHMETIC ADU \*w : Addition SBU \*w : Subtraction MLU \*w : Multiplication DVU \*w : Division RMU \*w : Remainder SLU \*w : Shift left SRU \*w : Shift right GROUP 5 - FLOATING POINT ARITHMETIC ADF \*w : Floating add (*) SBF \*w : Floating subtract (*) MLF \*w : Floating multiply (*) DVF \*w : Floating divide (*) NGF \*w : Floating negate (*) FIF \*w : Floating multiply and split integer and fraction part (*) FEF \*w : Split floating number in exponent and fraction part (*) GROUP 6 - POINTER ARITHMETIC ADP \*f : Add \*f to pointer on top of stack ADS \*w : Add \*w-byte value and pointer SBS \*w : Subtract pointers in same fragment and push diff as size \*w integer GROUP 7 - INCREMENT/DECREMENT/ZERO INC \*- : Increment word on top of stack by 1 (*) INL \*l : Increment local or parameter (*) INE \*g : Increment external (*) DEC \*- : Decrement word on top of stack by 1 (*) DEL \*l : Decrement local or parameter (*) DEE \*g : Decrement external (*) ZRL \*l : Zero local or parameter ZRE \*g : Zero external ZRF \*w : Load a floating zero of size \*w ZER \*w : Load \*w zero bytes GROUP 8 - CONVERT (stack: source, source size, dest. size (top)) CII \*- : Convert integer to integer (*) CUI \*- : Convert unsigned to integer (*) CFI \*- : Convert floating to integer (*) CIF \*- : Convert integer to floating (*) CUF \*- : Convert unsigned to floating (*) CFF \*- : Convert floating to floating (*) CIU \*- : Convert integer to unsigned CUU \*- : Convert unsigned to unsigned CFU \*- : Convert floating to unsigned GROUP 9 - LOGICAL AND \*w : Boolean and on two groups of \*w bytes IOR \*w : Boolean inclusive or on two groups of \*w bytes XOR \*w : Boolean exclusive or on two groups of \*w bytes COM \*w : Complement (one's complement of top \*w bytes) ROL \*w : Rotate left a group of \*w bytes ROR \*w : Rotate right a group of \*w bytes GROUP 10 - SETS INN \*w : Bit test on \*w byte set (bit number on top of stack) SET \*w : Create singleton \*w byte set with bit n on (n is top of stack) GROUP 11 - ARRAY LAR \*w : Load array element, descriptor contains integers of size \*w SAR \*w : Store array element AAR \*w : Load address of array element GROUP 12 - COMPARE CMI \*w : Compare \*w byte integers, Push negative, zero, positive for <, = or > CMF \*w : Compare \*w byte reals CMU \*w : Compare \*w byte unsigneds CMS \*w : Compare \*w byte values, can only be used for bit for bit equality test CMP \*- : Compare pointers TLT \*- : True if less, i.e. iff top of stack < 0 TLE \*- : True if less or equal, i.e. iff top of stack <= 0 TEQ \*- : True if equal, i.e. iff top of stack = 0 TNE \*- : True if not equal, i.e. iff top of stack non zero TGE \*- : True if greater or equal, i.e. iff top of stack >= 0 TGT \*- : True if greater, i.e. iff top of stack > 0 GROUP 13 - BRANCH BRA \*b : Branch unconditionally to label \*b BLT \*b : Branch less (pop 2 words, branch if top > second) BLE \*b : Branch less or equal BEQ \*b : Branch equal BNE \*b : Branch not equal BGE \*b : Branch greater or equal BGT \*b : Branch greater ZLT \*b : Branch less than zero (pop 1 word, branch negative) ZLE \*b : Branch less or equal to zero ZEQ \*b : Branch equal zero ZNE \*b : Branch not zero ZGE \*b : Branch greater or equal zero ZGT \*b : Branch greater than zero GROUP 14 - PROCEDURE CALL CAI \*- : Call procedure (procedure identifier on stack) CAL \*p : Call procedure (with identifier \*p) LFR \*s : Load function result RET \*z : Return (function result consists of top \*z bytes) GROUP 15 - MISCELLANEOUS ASP \*f : Adjust the stack pointer by \*f ASS \*w : Adjust the stack pointer by \*w-byte integer BLM \*z : Block move \*z bytes; first pop destination addr, then source addr BLS \*w : Block move, size is in \*w-byte integer on top of stack CSA \*w : Case jump; address of jump table at top of stack CSB \*w : Table lookup jump; address of jump table at top of stack DCH \*- : Follow dynamic chain, convert LB to LB of caller DUP \*s : Duplicate top \*s bytes DUS \*w : Duplicate top \*w bytes EXG \*w : Exchange top \*w bytes FIL \*g : File name (external 4 := \*g) GTO \*g : Non-local goto, descriptor at \*g LIM \*- : Load 16 bit ignore mask LIN \*n : Line number (external 0 := \*n) LNI \*- : Line number increment LOR \*r : Load register (0=LB, 1=SP, 2=HP) LPB \*- : Convert local base to argument base MON \*- : Monitor call NOP \*- : No operation RCK \*w : Range check; trap on error RTT \*- : Return from trap SIG \*- : Trap errors to proc identifier on top of stack, -2 resets default SIM \*- : Store 16 bit ignore mask STR \*r : Store register (0=LB, 1=SP, 2=HP) TRP \*- : Cause trap to occur (Error number on stack) .DE 0