NAME

adb − debugger

SYNOPSIS

adb [−w] [ objfil [ corfil ] ]

DESCRIPTION

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

Objfil is normally an executable program file, preferably containing a symbol table: if there is no symbol table 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 from adb are sent to the standard output.  If the −w flag is present, both objfil and corfil are created, if necessary, and opened for reading and writing so 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 following form:

[address]  [, count] [command] [;]

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

The interpretation of an address depends on the context in which it is used.  If a subprocess is being debugged, then addresses are interpreted in the address space of the subprocess.  If the operating system is being debugged, either post-mortem or using the special file /dev/kmem to interactive examine and/or modify memory, the maps are set to map the kernel virtual addresses, which start at 0x80000000.  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.  For example, 0o20 = 0t16 = 0x10 = sixteen.  If no prefix appears, the default radix is used:  (see the $d command).  The default radix is initially hexadecimal.  The hexadecimal digits are 0123456789abcdefABCDEF with the standard values.  Note that a hexadecimal number with a most significant digit that 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 or register name. Adb maintains a number of variables (see VARIABLES) named by single letters or digits.  If name is a register name, 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, which do not start with a digit.    The value of the symbol is taken from the symbol table in objfil. An initial _ or ~ is prepended to symbol, if required. 

_ symbol
In C, the ‘true name’ of an external symbol begins with _. It may be necessary to utter this name to distinguish 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. (This form is currently broken on the VAX; local variables can be examined only with sdb(1).)

(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. 

#exp Logical negation. 

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, the last format is used.  The format letters available are as follows. 

o2 Print 2 bytes in octal.  All octal numbers output by adb are preceded by 0. 

O4 Print 4 bytes in octal. 

q2 Print in signed octal. 

Q4 Print long signed octal. 

d2 Print in decimal. 

D4 Print long decimal. 

x2 Print 2 bytes in hexadecimal. 

X4 Print 4 bytes in hexadecimal. 

u2 Print as an unsigned decimal number. 

U4 Print long unsigned decimal. 

f4 Print the 32 bit value as a floating point number. 

F8 Print double floating point. 

b1 Print the addressed byte in octal. 

c1 Print the addressed character. 

C1 Print the addressed character using the standard escape convention where control characters are printed as ^X and the delete character is printed as ^?. 

sn Print the addressed characters until a zero character is reached. 

Sn Print a string using the ^X escape convention (see C above).  n is the length of the string, including its zero terminator. 

Y4 Print 4 bytes in date format (see ctime(3)).

in Print as VAX 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. 

a0 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

p4 Print the addressed value in symbolic form, using the same rules for symbol lookup as a. 

t0 When preceded by an integer, tabs to the next appropriate tab stop.  For example, 8t moves to the next 8-space tab stop. 

r0 Print a space. 

n0 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 the match is for 4 bytes at a time instead of 2.  If no match is found, dot is unchanged; otherwise, dot is set to the matched location.  If mask is omitted, −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, the remaining map parameters are left unchanged. If the ‘?’ or ‘/’ is followed by ‘\(**’, the second segment (b2,e2,f2) of the mapping is changed.  If the list is terminated by ‘?’ or ‘/’, the file (objfil or corfil respectively) is used for subsequent requests.  (For example, ‘/m?’ causes ‘/’ 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 as follows:

<f Read commands from the file f. If this command is executed in a file, further commands in the file are not seen. If f is omitted, the current input stream is terminated.  If a count given, is zero, the command is ignored.  The value of the count is placed in variable 9 before the first command in f is executed. 

<<f Similar to <, except it can be used in a file of commands without causing the file to be closed.  Variable 9 is saved during the execution of this command, and restored when it completes.  There is a (small) definite limit to the number of << files that can be opened immediately. 

>f Append output to the file f, which is created if it does not exist. If f is omitted, output is returned to the terminal. 

?  Print process id, (the signal which caused stoppage or termination), as well as the registers as $r.  This is the default if modifier is omitted. 

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. 

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

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 is omitted, or sets dot to zero, the breakpoint causes a stop. 

d Delete breakpoint at address.

r Run objfil as a subprocess.  If address is explicitly given, 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 entry to the subprocess. 

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

ss Similar to c, except the subprocess is single stepped count times.  If there is no current subprocess, objfil is run as a subprocess, as with 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. 

9 The count on the last $< or $<< command. 

On entry, the following are set from the system header in the corfil. If corfil does not appear to be a core file, 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 (0407, 0410 or 0413). 

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 \(**, 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 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

a.out
core

SEE ALSO

sdb(1), 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

Local variable addresses and names are recorded in the a.out file in a format known only to sdb(1).

Use of # for the unary logical negation operator is peculiar. 

It is not possible to clear all breakpoints. 

4th Berkeley Distribution  —  @(#)adb.1 1.1 Preliminary ERN0