20. Program Debugging

Contents:
The Sdb Debugger
The Dbx Debugger

This section presents the debugging utilities for the UNIX environment:

Sdb (available in SVR4 but not Solaris 2.0)
Dbx (Solaris 2.0 only)

These debuggers take an executable object file and its corefile-the core image file produced when objfile is executed. The debuggers then provide a controlled environment for the execution of the program.

If objfile and corefile are not specified, a.out is taken as the default object file and core as the default core image file.

Each debugging utility is listed among the UNIX commands in Section 2 of this guide.

20.1 The Sdb Debugger

Sdb, the symbolic debugger, is used for checking assembly programs, executable C and FORTRAN programs, and core files resulting from aborted programs. It has the following command-line syntax:

sdb [options ] [objfile [corefile [dir ]]]

A - in place of corefile will force sdb to ignore any core image file.

20.1.1 Options

-e: Ignore symbolic data; treat addresses as file offsets.
-s n: Don't stop processes that receive signal number n . See the signal system call for values of n . -s may be used more than once.
-V: Print version information (and exit if no objfile is given).
-w: Make objfile and corefile writable.
-W: Suppress warning messages about older files.

20.1.2 Command Specifiers

In the "Commands" section below, commands use the specifiers m , l , and n . m is the display format of an address. (Addresses are specified by a variable or a line number.) l is the address length. n stands for the line number.

20.1.2.1 Values for m

a: Characters starting at variable's address.
c: Character.
d: Decimal.
f: 32-bit floating.
g: 64-bit double precision floating.
i: Disassemble machine-language instructions; print address using numbers and symbols.
I: Same as i , but print address using numbers only.
o: Octal.
p: Pointer to procedure.
s: Print character(s) at address pointed to by (string pointer) variable.
u: Unsigned decimal.
x: Hexadecimal.

20.1.2.2 Values for l

Length specifiers are meaningful only with m values of c , d , o , u , or x .

b

One byte.

h

Two bytes (half word).

l

Four bytes (long word).

20.1.3 Commands

Refer to the previous specifiers when reviewing the sdb commands, which are grouped below:

20.1.4 Formatted Printing

`t`	Print a stack trace.
`T`	Print the top line of the stack trace.
`variable` `/` `clm`	Print variable according to length `l` and format `m` . Number `c` specifies how much memory (in units of `l` ) to display.
`n` `?` `lm` `variable` `:?` `lm`	Print from a.out and procedure `variable` according to length `l` and format `m` . Default `lm` is i .
`variable` `=` `lm` `n` `=` `lm` `number` `=` `lm`	Print the address of `variable` or line number `n` , in the format specified by `l` and `m` . Use the last form to convert `number` to the format specified by `l` and `m` . Default `lm` is lx .
`variable` `!` `value`	Assign `value` to `variable` .
`x`	Display the machine registers and the machine instructions.
`X`	Display the machine instructions.

20.1.5 Examining the Source

`e`	Print name of current file.
`e` `proc`	Set current file to file containing procedure `proc` .
`e` `file`	Set current file to `file` .
`e` `dir` `/`	Append directory `dir` to directory list.
`p`	Print current line.
`w`	Print ten lines surrounding the current line.
`z`	Print ten lines (starting at current); reset current line to last line.
`/` `regexp` `/`	Search ahead for regular expression `regexp` .
`?` `regexp` `?`	Search back for regular expression `regexp` .
`n`	Set current line to `n` and print it.
`count` `+`	Advance `count` lines; print new current line.
`count` `-`	Go back `count` lines; print new current line.

20.1.6 Executing the Source

`n` `a`	Set a breakpoint at line number `n` and inform the user.
[`n` ]`b` `commands`	Set breakpoint at line number `n` and optionally execute sdb `commands` (separated by ;) at breakpoint.
[`n` ]`c` `count`	Continue after a breakpoint or, if `count` is given, stop after `count` breakpoints. If `n` is specified, set a temporary breakpoint at line number `n` .
[`n` ]`C` `count`	Same as c , but reactivate any signal that stopped program.
`n` `g` `count`	Continue at line number `n` after a breakpoint. If `count` is given, ignore `count` breakpoints.
[`count` ] `r` `args`	Run the program with the specified arguments. Ignore `count` breakpoints.
[`count` ] `r`	Rerun the program with the previously specified arguments. Ignore `count` breakpoints.
[`count` ] `R`	Run the program with the no arguments. Ignore `count` breakpoints.
[`level` ] [`v` ]	This command is used when single-stepping via s , S , or m . v turns off verbose mode; omit v to turn on verbose mode. If `level` is omitted, print only source file or function name when either changes; otherwise, set `level` to 1 (print C source lines before execution) or 2 or higher (print C source lines and assembler statements).
`proc` (`a1` ,`a2` ,...)	Execute procedure `proc` with arguments `a1` , `a2` , etc. Arguments can be constants, local variable names, or register names. Append /m in order to print the returned value in format `m` (default is d ).

20.1.7 Breakpoint and Program Control

`B`	Print active breakpoints.
[`n` ]`d`	Delete breakpoint at line number `n` .
`D`	Remove all breakpoints.
`i` `count`	Single-step `count` machine-language instructions.
`I` `count`	Same as i , but reactivate any signal that stopped program.
`k`	Kill the program you're debugging.
`l`	Print the previous line executed.
`M`	Print the address maps.
`var` `$m` `count` `addr` `:m` `count`	Single-step `count` lines until the specified variable or address is modified. Omitting `count` specifies an infinite count.
`q`	Exit sdb.
`s` [`count` ]	Single-step `count` lines.
`S` [`count` ]	Same as s , but skip called functions.

20.1.8 Miscellaneous Commands

`#` `text`	Supply a text comment ignored by sdb.
`!` `cmd`	Execute `cmd` with sh .
`newline`	Display the next line or memory location, or disassemble the next instruction.
`EOF`	Scroll the display ten lines.
`<` `file`	Execute commands contained in `file` .
`string`	Print a quoted `string` . C escape characters are recognized.
`V`	Print the sdb version number.