as86 - Assembler for 8086..80386 processors
as86 [-0123agjuw] [-lm[list]] [-n name] [-o obj] [-b[bin]] [-s sym]
[-t textseg] src
as86_encap prog.s prog.v [prefix_] [as86_options]
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
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.
-0 start with 16-bit code segment, warn for all instructions > 8086
-1 start with 16-bit code segment, warn for all instructions >
-2 start with 16-bit code segment, warn for all instructions >
-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
-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.
* 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
% 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.
Direct register addressing, the jump copies BX into PC.
Simple indirect register addressing, the jump moves the contents
of the location specified by BX into the PC.
Immediate value, ax becomes 1234.
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.
Indexed addressing, both formats are ok, I think the first is
more correct but I tend to used the second. :-)
IF, ELSE, ELSEIF, ENDIF
String compare (str1,str2)
Generate user error.
.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
Label type definition
EXPORT PUBLIC .DEFINE
Export label defined in this object
ENTRY Force linker to include the specified label in a.out
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)
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 string copied to output.
.ASCIZ Ascii string copied to output with trailing nul byte.
.BLKB RMB .SPACE
Space is counted in bytes.
Space is counted in words. (2 bytes each)
COMM .COMM LCOMM .LCOMM
Common area data definition
Other useful pseudo operations.
EQU Define label
SET Define re-definable label
Set assemble location
BLOCK Set assemble location and stack old one
ENDB Return to stacked assemble location
Insert new file (no quotes on name)
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.
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)
Macro listings on/off (1,-1)
Macros, now working, the general form is like this.
IDENT Define object identity string.
SETDP Set DP value on 6809
MAP Set binary symbol table map number.
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.
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).
BCC BCS BEQ BGE BGT BHI BHIS BLE BLO BLOS BLT BMI BNE BPC BPL
BPS BVC BVS BR
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
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
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
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
The GASP list options have no support in as86.
as(1), ld86(1), bcc(1)
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
The .text and .data pseudo operators are not useful for raw binary
When using the org directive the assembler can generate object files
that may break ld86(1).
Mar, 1999 as86(1)