ADB(1)

NAME
adb - debugger

SYNOPSIS
adb [-w] [ objfil [ corfil ] ]

DESCRIPTION
Adb is a general purpose debugging program. It may be used to examine files and to provide a controlled environment for the execution of UNIX programs.

Objfil is normally an executable program file, preferably containing a symbol table; if not then the symbolic features of adb cannot be used although the file can still be examined. The default for objfil is a.out. Corfil is assumed to be a core image file produced after executing objfil; the default for corfil is core.

Requests to adb are read from the standard input and responses are to the standard output. If the -w flag is present then both objfil and corfil are created if necessary and opened for reading and writing so that files can be modified using adb. Adb ignores QUIT; INTERRUPT causes return to the next adb command.

In general requests to adb are of the form

[address] [, count] [command] [;]

If address is present then dot is set to address. Initially dot is set to 0. For most commands count specifies how many times the command will be executed. The default count is 1. Address and count are expressions.

The interpretation of an address depends on the context it is used in. If a subprocess is being debugged then addresses are interpreted in the usual way in the address space of the subprocess. For further details of address mapping see ADDRESSES.

EXPRESSIONS

.   The value of dot.

+   The value of dot incremented by the current increment.

^   The value of dot decremented by the current increment.

"   The last address typed.

integer
    A number. The prefixes 0o and 0O (``zero oh'') force interpretation in octal radix; the prefixes 0t and 0T force interpretation in decimal radix; the prefixes 0x and 0X force interpretation in hexadecimal radix. Thus 0o20 = 0t16 = 0x10 = sixteen. If no prefix appears, then the default radix is used; see the $d command. The default radix is initially hexadecimal. The hexadecimal digits are 0123456789abcdefABCDEF with the obvious values. Note that a hexadecimal number whose most significant digit would otherwise be an alphabetic character must have a 0x (or 0X) prefix (or a leading zero if the default radix is hexadecimal).

integer.fraction
    A 32 bit floating point number.

'cccc'
    The ASCII value of up to 4 characters. \ may be used to escape a '.

< name
    The value of name, which is either a variable name or a register name. Adb maintains a number of variables (see VARIABLES) named by single letters or digits. If name is a register name then the value of the register is obtained from the system header in corfil. The register names are those printed by the $r command.

symbol
    A symbol is a sequence of upper or lower case letters, underscores or digits, not starting with a digit. \ may be used to escape other characters. The value of the symbol is taken from the symbol table in objfil. An initial _ or ~ will be prepended to symbol if needed.

_ symbol
    In C, the `true name' of an external symbol begins with _. It may be necessary to utter this name to disinguish it from internal or hidden variables of a program.

routine.name
    The address of the variable name in the specified C routine. Both routine and name are symbols. If name is omitted the value is the address of the most recently activated C stack frame corresponding to routine.

(exp)
    The value of the expression exp.

Monadic operators

*exp
    The contents of the location addressed by exp in corfil.

@exp
    The contents of the location addressed by exp in objfil.

-exp
    Integer negation.

~exp
    Bitwise complement.

Dyadic operators are left associative and are less binding than monadic operators.

e1+e2
    Integer addition.

e1-e2
    Integer subtraction.

e1*e2
    Integer multiplication.

e1%e2
    Integer division.

e1&e2
    Bitwise conjunction.

e1|e2
    Bitwise disjunction.

e1#e2
    E1 rounded up to the next multiple of e2.

COMMANDS
Most commands consist of a verb followed by a modifier or list of modifiers. The following verbs are available. (The commands `?' and `/' may be followed by `*'; see ADDRESSES for further details.)

?f  Locations starting at address in objfil are printed according to the format f. dot is incremented by the sum of the increments for each format letter (q.v.).

/f  Locations starting at address in corfil are printed according to the format f and dot is incremented as for `?'.

=f  The value of address itself is printed in the styles indicated by the format f. (For i format `?' is printed for the parts of the instruction that reference subsequent words.)

A format consists of one or more characters that specify a style of printing. Each format character may be preceded by a decimal integer that is a repeat count for the format character. While stepping through a format dot is incremented by the amount given for each format letter. If no format is given then the last format is used. The format letters available are as follows.

    o	2 Print 2 bytes in octal. All octal numbers output by adb are preceded by 0.

    O	4 Print 4 bytes in octal.

    q	2 Print in signed octal.

    Q	4 Print long signed octal.

    d	2 Print in decimal.

    D	4 Print long decimal.

    r 2 Print in default radix.

    R 4 Print long default radix.

    x	2 Print 2 bytes in hexadecimal.

    X	4 Print 4 bytes in hexadecimal.

    u	2 Print as an unsigned decimal number.

    U	4 Print long unsigned decimal.

    f	4 Print the 32 bit value as a floating point number.

    F	8 Print double floating point.

    b	1 Print the addressed byte in octal.

    c	1 Print the addressed character.

    C	1 Print the addressed character using the following escape convention. Character values 000 to 040 are printed as @ followed by the corresponding character in the range 0100 to 0140. The character @ is printed as @@.

    s	n Print the addressed characters until a zero character is reached.

    S	n Print a string using the @ escape convention. n is the length of the string including its zero terminator.

    Y	4 Print 4 bytes in date format (see ctime(3)).

    i	n Print as PDP11 instructions. n is the number of bytes occupied by the instruction. This style of printing causes variables 1 and 2 to be set to the offset parts of the source and destination respectively.

    a	0 Print the value of dot in symbolic form. Symbols are checked to ensure that they have an appropriate type as indicated below.

        /    local or global data symbol
        ?    local or global text symbol
        =    local or global absolute symbol

    p	2 Print the addressed value in symbolic form using the same rules for symbol lookup as a.

    t	0 When preceded by an integer tabs to the next appropriate tab stop. For example, 8t moves to the next 8-space tab stop.

    r	0 Print a space.

    n	0 Print a newline.

    "..." 0
        Print the enclosed string.

    ^   Dot is decremented by the current increment. Nothing is printed.

    +   Dot is incremented by 1. Nothing is printed.

    -   Dot is decremented by 1. Nothing is printed.

newline
    Repeat the previous command with a count of 1.

[?/]l value mask
    Words starting at dot are masked with mask and compared with value until a match is found. If L is used then the match is for 4 bytes at a time instead of 2. If no match is found then dot is unchanged; otherwise dot is set to the matched location. If mask is omitted then -1 is used.

[?/]w value ...
    Write the 2-byte value into the addressed location. If the command is W, write 4 bytes. Odd addresses are not allowed when writing to the subprocess address space.

[?/]m b1 e1 f1[?/]
    New values for (b1, e1, f1) are recorded. If less than three expressions are given then the remaining map parameters are left unchanged. If the `?" or `/" is followed by `*" then the second segment (b2,e2,f2) of the mapping is changed. If the list is terminated by `?" or `/" then the file (objfil or corfil respectively) is used for subsequent requests. (So that, for example, `/m?" will cause `/" to refer to objfil.)

>name
    Dot is assigned to the variable or register named.

!   A shell is called to read the rest of the line following `!".

$modifier
    Miscellaneous commands. The available modifiers are:

    <f  Read commands from the file f and return.

    >f  Send output to the file f, which is created if it does not exist.

    r   Print the general registers and the instruction addressed by pc. Dot is set to pc.

    b   Print all breakpoints and their associated counts and commands.

    a   ALGOL 68 stack backtrace. If address is given then it is taken to be the address of the current frame (instead of r4). If count is given then only the first count frames are printed.

    c   C stack backtrace. If address is given then it is taken as the address of the current frame (instead of r5). If C is used then the names and (16 bit) values of all automatic and static variables are printed for each active function. If count is given then only the first count frames are printed.

    d   Set the default radix to address and report the new value. Note that address is interpreted in the (old) current radix. Thus ``10$d"" never changes the default radix. To make decimal the default radix, use ``0t10$d"".

    e   The names and values of external variables are printed.

    w   Set the page width for output to address (default 80).

    s   Set the limit for symbol matches to address (default 255).

    o   All integers input are regarded as octal.

    d   Reset integer input as described in EXPRESSIONS.

    q   Exit from adb.

    v   Print all non zero variables in octal.

    m   Print the address map.

:modifier
    Manage a subprocess. Available modifiers are:

    bc  Set breakpoint at address. The breakpoint is executed count-1 times before causing a stop. Each time the breakpoint is encountered the command c is executed. If this command sets dot to zero then the breakpoint causes a stop.

    d   Delete breakpoint at address.

    r   Run objfil as a subprocess. If address is given explicitly then the program is entered at this point; otherwise the program is entered at its standard entry point. count specifies how many breakpoints are to be ignored before stopping. Arguments to the subprocess may be supplied on the same line as the command. An argument starting with < or > causes the standard input or output to be established for the command. All signals are turned on on entry to the subprocess.

    cs  The subprocess is continued with signal s c s, see signal(2). If address is given then the subprocess is continued at this address. If no signal is specified then the signal that caused the subprocess to stop is sent. Breakpoint skipping is the same as for r.

    ss  As for c except that the subprocess is single stepped count times. If there is no current subprocess then objfil is run as a subprocess as for r. In this case no signal can be sent; the remainder of the line is treated as arguments to the subprocess.

    k   The current subprocess, if any, is terminated.

VARIABLES
Adb provides a number of variables. Named variables are set initially by adb but are not used subsequently. Numbered variables are reserved for communication as follows.

0   The last value printed.

1   The last offset part of an instruction source.

2   The previous value of variable 1.

On entry the following are set from the system header in the corfil. If corfil does not appear to be a core file then these values are set from objfil.

b   The base address of the data segment.

d   The data segment size.

e   The entry point.

m   The `magic" number (0405, 0407, 0410 or 0411).

s   The stack segment size.

t   The text segment size.

ADDRESSES
The address in a file associated with a written address is determined by a mapping associated with that file. Each mapping is represented by two triples (b1, e1, f1) and (b2, e2, f2) and the file address corresponding to a written address is calculated as follows.

b1≤address<e1 => file address=address+f1-b1, otherwise,

b2≤address<e2 => file address=address+f2-b2,

otherwise, the requested address is not legal. In some cases (e.g. for programs with separated I and D space) the two segments for a file may overlap. If a ? or / is followed by an * then only the second triple is used.

The initial setting of both mappings is suitable for normal a.out and core files. If either file is not of the kind expected then, for that file, b1 is set to 0, e1 is set to the maximum file size and f1 is set to 0; in this way the whole file can be examined with no address translation.

So that adb may be used on large files all appropriate values are kept as signed 32 bit integers.

FILES
/dev/mem
/dev/swap
a.out
core

SEE ALSO
ptrace(2), a.out(5), core(5)

DIAGNOSTICS
`Adb" when there is no current command or format. Comments about inaccessible files, syntax errors, abnormal termination of commands, etc. Exit status is 0, unless last command failed or returned nonzero status.

BUGS
A breakpoint set at the entry point is not effective on initial entry to the program.
When single stepping, system calls do not count as an executed instruction.
Local variables whose names are the same as an external variable may foul up the accessing of the external.