This chapter describes the Watcom Disassembler. It takes as input an object file (a file with extension .o) and produces, as output, the Intel assembly language equivalent. The Watcom compilers don't produce an assembly language listing directly from a source program. Instead, the Watcom Disassembler can be used to generate an assembly language listing from the object file generated by the compiler.
This chapter includes the following sections:
The Watcom Disassembler command-line syntax is as follows:
wdisasm [options] filespec [options]
The square brackets [ ] denote items that are optional.
The options supported by the Watcom Disassembler are:
The sections that follow describe the options.
By default, the Watcom Disassembler sends its output to the terminal. The l (``el'') option instructs the Watcom Disassembler to put the output in a listing file. The default file name of the listing file is the same as the file name of the object file. The default file extension of the listing file is .lst.
For example,
wdisasm calendar -l
In the above example, the Watcom Disassembler is instructed to disassemble the contents of the file calendar.o, and put the output in a listing file called calendar.lst.
An alternate form of this option is
l=list_file
With this form, you can specify the name of the listing file. When specifying a listing file, a file extension of .lst is assumed if none is specified.
For example,
wdisasm calendar -l=calendar.lis
In the above example, the Watcom Disassembler is instructed to disassemble the contents of the file calendar.o, and place the output in a listing file called calendar.lis.
The s option causes the source lines corresponding to the assembly language instructions to be placed in the listing file. The object file must contain line numbering information. That is, the d1 or d2 option must have been specified when the source file was compiled. If no line numbering information is present in the object file, the s option is ignored.
When the s option is specified, the order in which the source file name is determined is as follows:
In the following example, we have compiled the source file mysrc.c with d1 debugging information. We then disassemble it as follows:
wdisasm mysrc -s -l
In the above example, the Watcom Disassembler is instructed to disassemble the contents of the file mysrc.o and place the output in the listing file mysrc.lst. The source lines are extracted from the file mysrc.c.
An alternate form of this option is
s=source_file
With this form, you can specify the name of the source file. For example,
wdisasm mysrc -s=myprog.c-l
The above example produces the same result as in the previous example, except the source lines are extracted from the file myprog.c.
The c option permits you to specify one additional segment name or pattern for segments that contain executable code. Valid forms of the c option are:
where string is any sequence of characters, with letters treated in a case-insensitive manner. The ``*'' character is a wildcard character. You must protect the ``*'' with quotation marks to prevent the shell from attempting to expand it.
By default, the following segments are assumed to contain executable code:
Consider the following example:
wdisasm myprog "-c=T@*"
All segments whose name starts with the characters ``T@'' (in addition to those ending in CODE or TEXT) are assumed to contain executable code.
The i option permits you to specify the first character to be used for internal labels. Internal labels take the form Ln, where n is one or more digits. The default character L can be changed using the i option. The replacement character must be a letter (a-z, A-Z). A lowercase letter is converted to uppercase.
For example,
wdisasm calendar -i=x
The a option controls the format of the output produced to the listing file. When specified, the Watcom Disassembler produces a listing file that can be used as input to an assembler. When au is specified, the assembly syntax is that employed by UNIX systems.
For example,
wdisasm calendar -a -l=calendar.asm
In the above example, the Watcom Disassembler is instructed to disassemble the contents of the file calendar.o, and place the output in the file calendar.asm, so that it can be assembled by an assembler.
The b option causes an alternate form of the based or indexed addressing mode to be used in an instruction. By default, the following form is used:
mov ax,-2[bp]
If the b option is specified, the following form is used:
mov ax,[bp-2]
The e option controls the amount of information produced in the listing file. When specified, a list of all externally defined symbols is produced in the listing file.
For example,
wdisasm calendar -e
In the above example, the Watcom Disassembler is instructed to disassemble the contents of the file calendar.o and display the output, with a list of all external symbols, on the screen. A sample list of external symbols is shown below:
List of external symbols Symbol ---------------- ___iob 0000032f 00000210 000001f4 00000158 00000139 __CHK 00000381 00000343 000002eb 00000237 000000cb Box_ 000000f2 Calendar_ 000000a7 00000079 00000049 ClearScreen_ 00000016 fflush_ 00000334 00000215 000001f9 0000015d 0000013e int386_ 000003af 00000372 Line_ 000002db 000002b5 00000293 00000274 0000025a localtime_ 00000028 memset_ 00000308 PosCursor_ 0000031e 000001e1 00000148 00000123 000000b6 printf_ 00000327 00000208 000001ec 00000150 00000131 strlen_ 00000108 time_ 0000001d ----------------------------------------------------------
Each externally defined symbol is followed by a list of location counter values indicating where the symbol is referenced.
The p option controls the amount of information produced in the listing file. When specified, a list of all public symbols is produced in the listing file.
For example,
wdisasm calendar -p
In the above example, the Watcom Disassembler is instructed to disassemble the contents of the file calendar.o and display the output, with a list of all exported symbols, on the screen. A sample list of public symbols is shown below.
List of public symbols SYMBOL GROUP SEGMENT ADDRESS -------------------------------------------------- Box_ _TEXT 00000231 Calendar_ _TEXT 000000c5 ClearScreen_ _TEXT 0000037b Line_ _TEXT 000002e5 main_ _TEXT 00000000 PosCursor_ _TEXT 0000033d ---------------------------------------------------
The r option instructs the Watcom Disassembler to display register names in uppercase. The default is to display them in lowercase.
The u option instructs the Watcom Disassembler to display instruction opcode mnemonics in uppercase. The default is to display them in lowercase.
The m option instructs the Watcom Disassembler to retain C++ mangled names, rather than displaying their demangled form. The default is to interpret mangled C++ names, and display them in a somewhat more intelligible form.
Consider the following program contained in the file hello.c.
#include <stdio.h>
void main()
{
printf( "Hello world\n" );
}
Compile it with the d1 option. An object file called hello.o is produced. The d1 option causes line numbering information to be generated in the object file. We can use the Watcom Disassembler to disassemble the contents of the object file by issuing the following command:
wdisasm hello -l -e -p -s -r
The output is written in a listing file called hello.lst (the l option was specified). The output contains the following:
The source input file is called hello.c. The register names are displayed in upper case (the r option was specified). The output, shown below, is the result of using the Watcom disassembler.
Module: hello.c
Group: 'DGROUP' CONST,CONST2,_DATA,_BSS
Segment: _TEXT BYTE USE32 00000018 bytes
#include <stdio.h>
void main()
{
0000 68 08 00 00 00 main_ push 00000008H
0005 e8 00 00 00 00 call __CHK
printf( "Hello world\n" );
000a 68 00 00 00 00 push offset L1
000f e8 00 00 00 00 call printf_
0014 83 c4 04 add ESP,00000004H
}
0017 c3 ret
No disassembly errors
List of external symbols
Symbol
----------------
__CHK 00000006
printf_ 00000010
------------------------------------------------------------
Segment: CONST DWORD USE32 0000000d bytes
0000 48 65 6c 6c 6f 20 77 6f L1 - Hello wo
0008 72 6c 64 0a 00 - rld..
No disassembly errors
------------------------------------------------------------
List of public symbols
SYMBOL GROUP SEGMENT ADDRESS
---------------------------------------------------------
main_ _TEXT 00000000
------------------------------------------------------------
Let's create a form of the listing file that can be used as input to an assembler:
wdisasm hello -l=hello.asm -r -a
The output is placed in the file hello.asm. The output, shown below, is the result of using the Watcom Disassembler.
.386
NAME hello
EXTRN _cstart_ :BYTE
EXTRN printf_ :BYTE
EXTRN __CHK :BYTE
DGROUP GROUP CONST,CONST2,_DATA,_BSS
_TEXT SEGMENT BYTE PUBLIC USE32 'CODE'
ASSUME CS:_TEXT ,DS:DGROUP,SS:DGROUP
PUBLIC main_
main_ push 00000008H
call near ptr __CHK
push offset DGROUP:L1
call near ptr printf_
add ESP,00000004H
ret
_TEXT ENDS
CONST SEGMENT DWORD PUBLIC USE32 'DATA'
L1 DB 48H,65H,6cH,6cH,6fH,20H,77H,6fH
DB 72H,6cH,64H,0aH,00H
CONST ENDS
CONST2 SEGMENT DWORD PUBLIC USE32 'DATA'
CONST2 ENDS
_DATA SEGMENT DWORD PUBLIC USE32 'DATA'
_DATA ENDS
_BSS SEGMENT DWORD PUBLIC USE32 'BSS'
_BSS ENDS
END