as86 (1) - Linux Manuals
as86: Assembler for 8086..80386 processors
NAME
as86 - Assembler for 8086..80386 processors
SYNOPSIS
as86 [-0123agjuw] [-lm[list]] [-n name] [-o obj] [-b[bin]] [-s sym] [-t textseg] srcas86_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:
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.
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.
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.
The Gnu assembler preprocessor provides some reasonable implementations
of user biased pseudo opcodes.
It can be invoked in a form similar to:
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.
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).
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
Using GASP
as86
[...]
-
[-o obj] BUGS
The 6809 version does not support -0, -3, -a or -j.