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as86

Section: User Commands (1)
Updated: Mar, 1999
Index Return to Main Contents
 

NAME

as86 - Assembler for 8086..80386 processors  

SYNOPSIS

as86 [-0123agjuw] [-lm[list]] [-n name] [-o obj] [-b[bin]] [-s sym] [-t textseg] src

as86_encap prog.s prog.v [prefix_] [as86_options]

 

DESCRIPTION

as86 is an assembler for the 8086..80386 processors, it's syntax is closer to the intel/microsoft form rather than the more normal generic form of the unix system assembler.

The src file can be '-' to assemble the standard input.

This assembler can be compiled to support the 6809 cpu and may even work.

as86_encap is a shell script to call as86 and convert the created binary into a C file prog.v to be included in or linked with programs like boot block installers. The prefix_ argument is a prefix to be added to all variables defined by the source, it defaults to the name of the source file. The variables defined include prefix_start prefix_size and prefix_data to define and contain the code, plus integers containing the values of all exported labels. Either or both the prog.s and prog.v arguments can be '-' for standard in/out.

 

OPTIONS

-0
start with 16-bit code segment, warn for all instructions > 8086
-1
start with 16-bit code segment, warn for all instructions > 80186
-2
start with 16-bit code segment, warn for all instructions > 80286
-3
start with 32-bit code segment, don't warn for any instructions. (not even 486 or 586)
-a
enable partial compatibility with Minix asld. This swaps the interpretation of round brackets and square brackets as well as making alterations to the code generation and syntax for 16bit jumps and calls. ("jmp @(bx)" is then a valid instruction)
-g
only put global symbols in object or symbol file
-j
replace all short jumps with similar 16 or 32 bit jumps, the 16 bit conditional branches are encoded as a short conditional and a long unconditional branch.
-O
this causes the assembler to add extra passes to try to use forward references to reduce the bytes needed for some instructions. If the labels move on the last pass the assembler will keep adding passes until the labels all stabilise (to a maximum of 30 passes) It's probably not a good idea to use this with hand written assembler use the explicit br bmi bcc style opcodes for 8086 code or the jmp near style for conditional i386 instructions and make sure all variables are defined before they are used.
-l
produce list file, filename may follow
-m
print macro expansions in listing
-n
name of module follows (goes in object instead of source name)
-o
produce object file, filename follows
-b
produce a raw binary file, filename may follow. This is a 'raw' binary file with no header, if there's no -s option the file starts at location 0.
-s
produce an ASCII symbol file, filename follows. The format of this table is designed to be easy to parse for encapsulation and related activities in relation to binary files created with the -b option. If a binary file doesn't start at location zero the first two items in the table are the start and end addresses of the binary file.
-u
assume undefined symbols are imported-with-unspecified segment.
-w-
allow the assembler to print warning messages.
-t n
move all text segment data in segment n+3.
 

AS86 SOURCE

Special characters
*
Address of the start of the current line.
; !
Either of these marks the start of a comment. In addition any 'unexpected' character at the start of a line is assumed to be a comment (but it's also displayed to the terminal).
$
Prefix for hexadecimal numbers, the 'C' syntax, eg 0x1234, is also accepted.
%
Prefix for binary numbers.
#
Prefix for immediate operands.
[ ]
Specifies an indirect operand.
Unlike MASM the assembler has no type information on labels just a segment and offset. This means that the way this operator and the immediate prefix work are like traditional assemblers.

Examples:
       mov ax,bx

       jmp bx

Direct register addressing, the jump copies BX into PC.

        mov ax,[bx]
        jmp [bx]
Simple indirect register addressing, the jump moves the contents of the location specified by BX into the PC.

       mov ax,#1234

Immediate value, ax becomes 1234.

        mov ax,1234
        mov ax,_hello
        mov ax,[_hello]
Absolute addressing, ax is set to contents of location 1234. Note the third option is not strictly consistant but is in place mainly for asld compatibility.

        mov ax,_table[bx]
        mov ax,_table[bx+si]
        mov eax,_table[ebx*4]

        mov ax,[bx+_table]
        mov ax,[bx+si+_table]
        mov eax,[ebx*4+_table]
Indexed addressing, both formats are ok, I think the first is more correct but I tend to used the second. :-)
Conditionals
IF, ELSE, ELSEIF, ENDIF
Numeric condition
IFC, ELSEIFC
String compare (str1,str2)
FAIL .FAIL
Generate user error. Segment related
.TEXT .ROM .DATA .BSS
Set current segment. These can be preceded by the keyword .SECT
LOC
Set numeric segment 0=TEXT, 3=DATA,ROM,BSS, 14=MAX. The segment order set by the linker is now 0,4,5,6,7,8,9,A,B,C,D,E,1,2,3. Segment 0 and all segments above 3 are assumed to be text segment. Note the 64k size restrictions are not imposed for segments 3-14. Label type definition
EXPORT PUBLIC .DEFINE
Export label defined in this object
ENTRY
Force linker to include the specified label in a.out
.GLOBL .GLOBAL
Define label as external and force import even if it isn't used.
EXTRN EXTERN IMPORT .EXTERN
Import list of externally defined labels
NB: It doesn't make sense to use imports for raw binary files.
.ENTER
Mark entry for old binary file (obs) Data definition
DB .DATA1 .BYTE FCB
List of 1 byte objects.
DW .DATA2 .SHORT FDB .WORD
List of 2 byte objects.
DD .DATA4 .LONG
List of 4 byte objects.
.ASCII FCC
Ascii string copied to output.
.ASCIZ
Ascii string copied to output with trailing nul byte. Space definition
.BLKB RMB .SPACE
Space is counted in bytes.
.BLKW .ZEROW
Space is counted in words. (2 bytes each)
COMM .COMM LCOMM .LCOMM
Common area data definition Other useful pseudo operations.
.ALIGN .EVEN
Alignment
EQU
Define label
SET
Define re-definable label
ORG .ORG
Set assemble location
BLOCK
Set assemble location and stack old one
ENDB
Return to stacked assemble location
GET INCLUDE
Insert new file (no quotes on name)
USE16 [cpu]
Define default operand size as 16 bit, argument is cpu type the code is expected to run on (86, 186, 286, 386, 486, 586) instructions for cpus later than specified give a warning.
USE32 [cpu]
Define default operand size as 32 bit, argument is cpu type the code is expected to run on (86, 186, 286, 386, 486, 586) instructions for cpus later than specified give a warning. If the cpu is not mentioned the assembler ensures it is >= 80386.
END
End of compilation for this file.
.WARN
Switch warnings
.LIST
Listings on/off (1,-1)
.MACLIST
Macro listings on/off (1,-1) Macros, now working, the general form is like this.


    MACRO sax
       mov ax,#?1
    MEND
    sax(1)

Unimplemented/unused.
IDENT
Define object identity string.
SETDP
Set DP value on 6809
MAP
Set binary symbol table map number.
Registers

BP BX DI SI
EAX EBP EBX ECX EDI EDX ESI ESP
AX CX DX SP
AH AL BH BL CH CL DH DL
CS DS ES FS GS SS
CR0 CR2 CR3 DR0 DR1 DR2 DR3 DR6 DR7
TR3 TR4 TR5 TR6 TR7 ST
Operand type specifiers
BYTE DWORD FWORD FAR PTR PWORD QWORD TBYTE WORD NEAR

The 'near and 'far' do not allow multi-segment programming, all 'far' operations are specified explicitly through the use of the instructions: jmpi, jmpf, callf, retf, etc. The 'Near' operator can be used to force the use of 80386 16bit conditional branches. The 'Dword' and 'word' operators can control the size of operands on far jumps and calls.

General instructions.
These are in general the same as the instructions found in any 8086 assembler, the main exceptions being a few 'Bcc' (BCC, BNE, BGE, etc) instructions which are shorthands for a short branch plus a long jump and 'BR' which is the longest unconditional jump (16 or 32 bit).
Long branches
BCC BCS BEQ BGE BGT BHI BHIS BLE BLO BLOS BLT BMI BNE BPC BPL BPS BVC BVS BR
Intersegment
CALLI CALLF JMPI JMPF
Segment modifier instructions
ESEG FSEG GSEG SSEG
Byte operation instructions
ADCB ADDB ANDB CMPB DECB DIVB IDIVB IMULB INB INCB MOVB MULB NEGB NOTB ORB OUTB RCLB RCRB ROLB RORB SALB SARB SHLB SHRB SBBB SUBB TESTB XCHGB XORB
Standard instructions
AAA AAD AAM AAS ADC ADD AND ARPL BOUND BSF BSR BSWAP BT BTC BTR BTS CALL CBW CDQ CLC CLD CLI CLTS CMC CMP CMPS CMPSB CMPSD CMPSW CMPW CMPXCHG CSEG CWD CWDE DAA DAS DEC DIV DSEG ENTER HLT IDIV IMUL IN INC INS INSB INSD INSW INT INTO INVD INVLPG INW IRET IRETD J JA JAE JB JBE JC JCXE JCXZ JE JECXE JECXZ JG JGE JL JLE JMP JNA JNAE JNB JNBE JNC JNE JNG JNGE JNL JNLE JNO JNP JNS JNZ JO JP JPE JPO JS JZ LAHF LAR LDS LEA LEAVE LES LFS LGDT LGS LIDT LLDT LMSW LOCK LODB LODS LODSB LODSD LODSW LODW LOOP LOOPE LOOPNE LOOPNZ LOOPZ LSL LSS LTR MOV MOVS MOVSB MOVSD MOVSW MOVSX MOVW MOVZX MUL NEG NOP NOT OR OUT OUTS OUTSB OUTSD OUTSW OUTW POP POPA POPAD POPF POPFD PUSH PUSHA PUSHAD PUSHF PUSHFD RCL RCR RDMSR REP REPE REPNE REPNZ REPZ RET RETF RETI ROL ROR SAHF SAL SAR SBB SCAB SCAS SCASB SCASD SCASW SCAW SEG SETA SETAE SETB SETBE SETC SETE SETG SETGE SETL SETLE SETNA SETNAE SETNB SETNBE SETNC SETNE SETNG SETNGE SETNL SETNLE SETNO SETNP SETNS SETNZ SETO SETP SETPE SETPO SETS SETZ SGDT SHL SHLD SHR SHRD SIDT SLDT SMSW STC STD STI STOB STOS STOSB STOSD STOSW STOW STR SUB TEST VERR VERW WAIT WBINVD WRMSR XADD XCHG XLAT XLATB XOR
Floating point
F2XM1 FABS FADD FADDP FBLD FBSTP FCHS FCLEX FCOM FCOMP FCOMPP FCOS FDECSTP FDISI FDIV FDIVP FDIVR FDIVRP FENI FFREE FIADD FICOM FICOMP FIDIV FIDIVR FILD FIMUL FINCSTP FINIT FIST FISTP FISUB FISUBR FLD FLD1 FLDL2E FLDL2T FLDCW FLDENV FLDLG2 FLDLN2 FLDPI FLDZ FMUL FMULP FNCLEX FNDISI FNENI FNINIT FNOP FNSAVE FNSTCW FNSTENV FNSTSW FPATAN FPREM FPREM1 FPTAN FRNDINT FRSTOR FSAVE FSCALE FSETPM FSIN FSINCOS FSQRT FST FSTCW FSTENV FSTP FSTSW FSUB FSUBP FSUBR FSUBRP FTST FUCOM FUCOMP FUCOMPP FWAIT FXAM FXCH FXTRACT FYL2X FYL2XP1
 

Using GASP

The Gnu assembler preprocessor provides some reasonable implementations of user biased pseudo opcodes.

It can be invoked in a form similar to:

gasp
[-a...] file.s [file2.s] |
as86 [...] - [-o obj] [-b bin] Be aware though that Gasp generates an error for .org commands, if you're not using alternate syntax you can use org instead, otherwise use block and endb. The directive export is translated into .global, which forces an import, if you are making a file using -b use public or .define instead.

The GASP list options have no support in as86.

 

SEE ALSO

as(1), ld86(1), bcc(1)  

BUGS

The 6809 version does not support -0, -3, -a or -j.

If this assembler is compiled with BCC this is classed as a 'small' compiler, so there is a maximum input line length of 256 characters and the instruction to cpu checking is not included.

The checking for instructions that work on specific cpus is probably not complete, the distinction between 80186 and 80286 is especially problematic.

The .text and .data pseudo operators are not useful for raw binary files.

When using the org directive the assembler can generate object files that may break ld86(1).


 

Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
AS86 SOURCE
Using GASP
SEE ALSO
BUGS




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