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<head>
<title>db(1) - Plan 9 from User Space</title>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
</head>
<body bgcolor=#ffffff>
<table border=0 cellpadding=0 cellspacing=0 width=100%>
<tr height=10><td>
<tr><td width=20><td>
<tr><td width=20><td><b>DB(1)</b><td align=right><b>DB(1)</b>
<tr><td width=20><td colspan=2>
<br>
<p><font size=+1><b>NAME </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
db – debugger<br>
</table>
<p><font size=+1><b>SYNOPSIS </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<tt><font size=+1>db</font></tt> [ <i>option ...</i> ] [ <i>textfile</i> ] [ <i>pid</i> | <i>corefile</i> ]<br>
</table>
<p><font size=+1><b>DESCRIPTION </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<i>Db</i> is a general purpose debugging program. It may be used to examine
files and to provide a controlled environment for the execution
of programs.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
A <i>textfile</i> is a file containing the text and initialized data
of an executable program. A <i>pid</i> or <i>corefile</i> specifies the memory
image of a process. A <i>pid</i> gives the id of an executing process
to be accessed via <a href="../man2/ptrace.html"><i>ptrace</i>(2)</a>. A <i>corefile</i> specifies the name of
a core dump (see <a href="../man5/core.html"><i>core</i>(5)</a> on your system of choice) containing
the
memory image of a terminated process. This manual refers to the
memory image specified by <i>pid</i> or <i>corefile</i> as a <i>memfile</i>.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
A <i>map</i> associated with each <i>textfile</i> or <i>memfile</i> supports accesses
to instructions and data in the file; see ‘Addresses’.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
An argument consisting entirely of digits is assumed to be a process
id; otherwise, it is the name of a <i>textfile</i> or <i>corefile</i>. When
a <i>textfile</i> is given, the textfile map is associated with it. If
only a <i>memfile</i> is given, the textfile map is derived from the
corresponding <i>textfile</i>, if it can be determined (this varies from
system to
system). When a <i>memfile</i> is given, the memfile map is associated
with it; otherwise the map is undefined and accesses to it are
not permitted.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
Commands to <i>db</i> are read from the standard input and responses
are to the standard output. The options are<br>
<tt><font size=+1>−w</font></tt> Open <i>textfile</i> and <i>memfile</i> for writing as well as reading.<br>
<tt><font size=+1>−I</font></tt><i>path<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
Directory in which to look for relative path names in <tt><font size=+1>$<</font></tt> and <tt><font size=+1>$<<</font></tt>
commands.<br>
</table>
<tt><font size=+1>−m</font></tt><i>machine<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
Assume instructions are for the given CPU type (possible names
include <tt><font size=+1>386</font></tt> and <tt><font size=+1>powerpc</font></tt>; adding the suffix <tt><font size=+1>−co</font></tt> as in <tt><font size=+1>386−co</font></tt> and
<tt><font size=+1>powerpc−co</font></tt> selects disassembly in the manufacturer’s syntax, if
available, rather than the default Plan 9 syntax).
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</table>
Most <i>db</i> commands have the following form:<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
[<i>address</i>] [<tt><font size=+1>,</font></tt> <i>count</i>] [<i>command</i>]
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</table>
If <i>address</i> is present then the current position, called ‘dot’,
is set to <i>address</i>. Initially dot is set to 0. Most commands are
repeated <i>count</i> times with dot advancing between repetitions. The
default <i>count</i> is 1. <i>Address</i> and <i>count</i> are expressions. Multiple
commands on one line must be separated by <tt><font size=+1>;</font></tt>.
<p><font size=+1><b>Expressions </b></font><br>
Expressions are evaluated as long <i>ints</i>.<br>
<tt><font size=+1>.</font></tt> The value of dot.<br>
<tt><font size=+1>+</font></tt> The value of dot incremented by the current increment.<br>
<tt><font size=+1>^</font></tt> The value of dot decremented by the current increment.<br>
<tt><font size=+1>"</font></tt> The last <i>address</i> typed.<br>
<i>integer<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
A number, in decimal radix by default. The prefixes <tt><font size=+1>0</font></tt> and <tt><font size=+1>0o</font></tt> and
<tt><font size=+1>0O</font></tt> (zero oh) force interpretation in octal radix; the prefixes
<tt><font size=+1>0t</font></tt> and <tt><font size=+1>0T</font></tt> force interpretation in decimal radix; the prefixes
<tt><font size=+1>0x</font></tt>, <tt><font size=+1>0X</font></tt>, and <tt><font size=+1>#</font></tt> force interpretation in hexadecimal radix. Thus
<tt><font size=+1>020</font></tt>, <tt><font size=+1>0o20</font></tt>, <tt><font size=+1>0t16</font></tt>, and <tt><font size=+1>#10</font></tt> all represent sixteen.
</table>
<i>integer</i><tt><font size=+1>.</font></tt><i>fraction<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
A single-precision floating point number.<br>
</table>
<tt><font size=+1>'</font></tt><i>c</i><tt><font size=+1>'</font></tt> The 16-bit value of a character. <tt><font size=+1>\</font></tt> may be used to escape a
<tt><font size=+1>'</font></tt>.<br>
<tt><font size=+1><</font></tt><i>name<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
The value of <i>name</i>, which is a register name. The register names
are those printed by the <tt><font size=+1>$r</font></tt> command.<br>
</table>
<i>symbol<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
A <i>symbol</i> is a sequence of upper or lower case letters, underscores
or digits, not starting with a digit. <tt><font size=+1>\</font></tt> may be used to escape
other characters. The location of the <i>symbol</i> is calculated from
the symbol table in <i>textfile</i>.<br>
</table>
<i>routine</i><tt><font size=+1>.</font></tt><i>name<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
The address of the variable <i>name</i> in the specified C routine. Both
<i>routine</i> and <i>name</i> are <i>symbols</i>. If <i>name</i> is omitted the value is
the address of the most recently activated stack frame corresponding
to <i>routine</i>; if <i>routine</i> is omitted, the active procedure is assumed.<br>
</table>
<i>file</i><tt><font size=+1>:</font></tt><i>integer<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
The address of the instruction corresponding to the source statement
at the indicated line number of the file. If the source line contains
no executable statement, the address of the instruction associated
with the nearest executable source line is returned. Files begin
at line 1. If multiple files of the same name
are loaded, an expression of this form resolves to the first file
encountered in the symbol table.<br>
</table>
<tt><font size=+1>(</font></tt><i>exp</i><tt><font size=+1>)<br>
</font></tt>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
The value of the expression <i>exp</i>.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</table>
<i>Monadic operators<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<tt><font size=+1>*</font></tt><i>exp</i> The contents of the location addressed by <i>exp</i> in <i>memfile</i>.<br>
<tt><font size=+1>@</font></tt><i>exp</i> The contents of the location addressed by <i>exp</i> in <i>textfile</i>.<br>
<tt><font size=+1>−</font></tt><i>exp</i> Integer negation.<br>
<tt><font size=+1>~</font></tt><i>exp</i> Bitwise complement.<br>
<tt><font size=+1>%</font></tt><i>exp</i> When used as an <i>address</i>, <i>exp</i> is an offset into the segment
named <i>ublock</i>; see ‘Addresses’.<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</table>
<i>Dyadic operators</i> are left-associative and are less binding than
monadic operators.<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<i>e1</i><tt><font size=+1>+</font></tt><i>e2</i>Integer addition.<br>
<i>e1</i><tt><font size=+1>−</font></tt><i>e2</i>Integer subtraction.<br>
<i>e1</i><tt><font size=+1>*</font></tt><i>e2</i>Integer multiplication.<br>
<i>e1</i><tt><font size=+1>%</font></tt><i>e2</i>Integer division.<br>
<i>e1</i><tt><font size=+1>&</font></tt><i>e2</i>Bitwise conjunction.<br>
<i>e1</i><tt><font size=+1>|</font></tt><i>e2</i>Bitwise disjunction.<br>
<i>e1</i><tt><font size=+1>#</font></tt><i>e2E1</i> rounded up to the next multiple of <i>e2</i>.<br>
</table>
<p><font size=+1><b>Commands </b></font><br>
Most commands have the following syntax:<br>
<tt><font size=+1>?</font></tt><i>f</i> Locations starting at <i>address</i> in <i>textfile</i> are printed according
to the format <i>f</i>.<br>
<tt><font size=+1>/</font></tt><i>f</i> Locations starting at <i>address</i> in <i>memfile</i> are printed according
to the format <i>f</i>.<br>
<tt><font size=+1>=</font></tt><i>f</i> The value of <i>address</i> itself is printed according to the format
<i>f</i>.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
A <i>format</i> 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. If no
format is given then the last format is used.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
Most format letters fetch some data, print it, and advance (a
local copy of) dot by the number of bytes fetched. The total number
of bytes in a format becomes the <i>current</i>increment<i>.<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<tt><font size=+1>o</font></tt> Print two-byte integer in octal.<br>
<tt><font size=+1>O</font></tt> Print four-byte integer in octal.<br>
<tt><font size=+1>q</font></tt> Print two-byte integer in signed octal.<br>
<tt><font size=+1>Q</font></tt> Print four-byte integer in signed octal.<br>
<tt><font size=+1>d</font></tt> Print two-byte integer in decimal.<br>
<tt><font size=+1>D</font></tt> Print four-byte integer in decimal.<br>
<tt><font size=+1>V</font></tt> Print eight-byte integer in decimal.<br>
<tt><font size=+1>Z</font></tt> Print eight-byte integer in unsigned decimal.<br>
<tt><font size=+1>x</font></tt> Print two-byte integer in hexadecimal.<br>
<tt><font size=+1>X</font></tt> Print four-byte integer in hexadecimal.<br>
<tt><font size=+1>Y</font></tt> Print eight-byte integer in hexadecimal.<br>
<tt><font size=+1>u</font></tt> Print two-byte integer in unsigned decimal.<br>
<tt><font size=+1>U</font></tt> Print four-byte integer in unsigned decimal.<br>
<tt><font size=+1>f</font></tt> Print as a single-precision floating point number.<br>
<tt><font size=+1>F</font></tt> Print double-precision floating point.<br>
<tt><font size=+1>b</font></tt> Print the addressed byte in hexadecimal.<br>
<tt><font size=+1>c</font></tt> Print the addressed byte as an ASCII character.<br>
<tt><font size=+1>C</font></tt> Print the addressed byte as a character. Printable ASCII characters
are represented normally; others are printed in the form <tt><font size=+1>\xnn</font></tt>.<br>
<tt><font size=+1>s</font></tt> Print the addressed characters, as a UTF string, until a zero
byte is reached. Advance dot by the length of the string, including
the zero terminator.<br>
<tt><font size=+1>S</font></tt> Print a string using the escape convention (see <tt><font size=+1>C</font></tt> above).<br>
<tt><font size=+1>r</font></tt> Print as UTF the addressed two-byte integer (rune).<br>
<tt><font size=+1>R</font></tt> Print as UTF the addressed two-byte integers as runes until a
zero rune is reached. Advance dot by the length of the string,
including the zero terminator.<br>
<tt><font size=+1>i</font></tt> Print as machine instructions. Dot is incremented by the size
of the instruction.<br>
<tt><font size=+1>I</font></tt> As <tt><font size=+1>i</font></tt> above, but print the machine instructions in an alternate
form if possible.<br>
<tt><font size=+1>M</font></tt> Print the addressed machine instruction in a machine-dependent
hexadecimal form.<br>
<tt><font size=+1>a</font></tt> Print the value of dot in symbolic form. Dot is unaffected.<br>
<tt><font size=+1>A</font></tt> Print the value of dot in hexadecimal. Dot is unaffected.<br>
<tt><font size=+1>z</font></tt> Print the function name, source file, and line number corresponding
to dot (textfile only). Dot is unaffected.<br>
<tt><font size=+1>p</font></tt> Print the addressed value in symbolic form. Dot is advanced by
the size of a machine address.<br>
<tt><font size=+1>t</font></tt> When preceded by an integer, tabs to the next appropriate tab
stop. For example, <tt><font size=+1>8t</font></tt> moves to the next 8-space tab stop. Dot
is unaffected.<br>
<tt><font size=+1>n</font></tt> Print a newline. Dot is unaffected.<br>
<tt><font size=+1>"</font></tt>...<tt><font size=+1>"</font></tt> Print the enclosed string. Dot is unaffected.<br>
<tt><font size=+1>^</font></tt> Dot is decremented by the current increment. Nothing is printed.<br>
<tt><font size=+1>+</font></tt> Dot is incremented by 1. Nothing is printed.<br>
<tt><font size=+1>−</font></tt> Dot is decremented by 1. Nothing is printed.<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</table>
Other commands include:<br>
newline<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
Update dot by the current increment. Repeat the previous command
with a <i>count</i> of 1.<br>
</table>
[<tt><font size=+1>?/</font></tt>]<tt><font size=+1>l</font></tt> <i>value mask<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
Words starting at dot are masked with <i>mask</i> and compared with <i>value</i>
until a match is found. If <tt><font size=+1>l</font></tt> is used, the match is for a two-byte
integer; <tt><font size=+1>L</font></tt> matches four bytes. If no match is found then dot is
unchanged; otherwise dot is set to the matched location. If <i>mask</i>
is omitted then ~0 is used.
</table>
[<tt><font size=+1>?/</font></tt>]<tt><font size=+1>w</font></tt> <i>value ...<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
Write the two-byte <i>value</i> into the addressed location. If the command
is <tt><font size=+1>W</font></tt>, write four bytes.<br>
</table>
[<tt><font size=+1>?/</font></tt>]<tt><font size=+1>m</font></tt> <i>s b e f</i> [<tt><font size=+1>?</font></tt>]<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
New values for (<i>b, e, f</i>) in the segment named <i>s</i> are recorded.
Valid segment names are <i>text</i>, <i>data</i>, or <i>ublock</i>. If less than three
address expressions are given, the remaining parameters are left
unchanged. If the list is terminated by <tt><font size=+1>?</font></tt> or <tt><font size=+1>/</font></tt> then the file (<i>textfile</i>
or <i>memfile</i> respectively) is used for subsequent
requests. For example, <tt><font size=+1>/m?</font></tt> causes <tt><font size=+1>/</font></tt> to refer to <i>textfile</i>.<br>
</table>
<tt><font size=+1>></font></tt><i>name<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
Dot is assigned to the variable or register named.<br>
</table>
<tt><font size=+1>!</font></tt> The rest of the line is passed to <a href="../man1/rc.html"><i>rc</i>(1)</a> for execution.<br>
<tt><font size=+1>$</font></tt><i>modifier<br>
</i>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
Miscellaneous commands. The available <i>modifiers</i> are:<br>
<tt><font size=+1><</font></tt><i>f</i> Read commands from the file <i>f</i>. If this command is executed in
a file, further commands in the file are not seen. If <i>f</i> is omitted,
the current input stream is terminated. If a <i>count</i> is given, and
is zero, the command is ignored.<br>
<tt><font size=+1><<</font></tt><i>f</i> Similar to <tt><font size=+1><</font></tt> except it can be used in a file of commands without
causing the file to be closed. There is a (small) limit to the
number of <tt><font size=+1><<</font></tt> files that can be open at once.<br>
<tt><font size=+1>></font></tt><i>f</i> Append output to the file <i>f</i>, which is created if it does not
exist. If <i>f</i> is omitted, output is returned to the terminal.<br>
<tt><font size=+1>?</font></tt> Print process id, the condition which caused stopping or termination,
the registers and the instruction addressed by <tt><font size=+1>pc</font></tt>. This is the
default if <i>modifier</i> is omitted.<br>
<tt><font size=+1>r</font></tt> Print the general registers and the instruction addressed by
<tt><font size=+1>pc</font></tt>. Dot is set to <tt><font size=+1>pc</font></tt>.<br>
<tt><font size=+1>R</font></tt> Like <tt><font size=+1>$r</font></tt>, but include miscellaneous processor control registers
and floating point registers.<br>
<tt><font size=+1>f</font></tt> Print floating-point register values as single-precision floating
point numbers.<br>
<tt><font size=+1>F</font></tt> Print floating-point register values as double-precision floating
point numbers.<br>
<tt><font size=+1>b</font></tt> Print all breakpoints and their associated counts and commands.
‘B’ produces the same results.<br>
<tt><font size=+1>c</font></tt> Stack backtrace. If <i>address</i> is given, it specifies the address
of a pair of 32-bit values containing the <tt><font size=+1>sp</font></tt> and <tt><font size=+1>pc</font></tt> of an active
process. This allows selecting among various contexts of a multi-threaded
process. If <tt><font size=+1>C</font></tt> is used, the names and (long) values of all parameters,
automatic and static variables are
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printed for each active function. If <i>count</i> is given, only the
first <i>count</i> frames are printed.<br>
</table>
<tt><font size=+1>a</font></tt> Attach to the running process whose pid is contained in <i>address</i>.<br>
<tt><font size=+1>e</font></tt> The names and values of all external variables are printed.<br>
<tt><font size=+1>w</font></tt> Set the page width for output to <i>address</i> (default 80).<br>
<tt><font size=+1>q</font></tt> Exit from <i>db</i>.<br>
<tt><font size=+1>m</font></tt> Print the address maps.<br>
<tt><font size=+1>k</font></tt> Simulate kernel memory management.<br>
<tt><font size=+1>M</font></tt><i>machine<br>
</i>
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Set the <i>machine</i> type used for disassembling instructions.<br>
</table>
</table>
<tt><font size=+1>:</font></tt><i>modifier<br>
</i>
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Manage a subprocess. Available modifiers are:<br>
<tt><font size=+1>h</font></tt> Halt an asynchronously running process to allow breakpointing.
Unnecessary for processes created under <i>db</i>, e.g. by <tt><font size=+1>:r</font></tt>.<br>
<tt><font size=+1>b</font></tt><i>c</i> Set breakpoint at <i>address</i>. The breakpoint is executed <i>count</i>–1
times before causing a stop. Also, if a command <i>c</i> is given it
is executed at each breakpoint and if it sets dot to zero the
breakpoint causes a stop.<br>
<tt><font size=+1>d</font></tt> Delete breakpoint at <i>address</i>.<br>
<tt><font size=+1>r</font></tt> Run <i>textfile</i> as a subprocess. If <i>address</i> is given the program
is entered at that point; otherwise the standard entry point is
used. <i>Count</i> 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
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starting with < or > causes the standard input or output to be established
for the command.<br>
</table>
<tt><font size=+1>c</font></tt><i>s</i> The subprocess is continued. If <i>s</i> is omitted or nonzero, the
subprocess is sent the note that caused it to stop. If 0 is specified,
no note is sent. (If the stop was due to a breakpoint or single-step,
the corresponding note is elided before continuing.) Breakpoint
skipping is the same as for <tt><font size=+1>r</font></tt>.
<tt><font size=+1>s</font></tt><i>s</i> As for <tt><font size=+1>c</font></tt> except that the subprocess is single stepped for <i>count</i>
machine instructions. If a note is pending, it is received before
the first instruction is executed. If there is no current subprocess
then <i>textfile</i> is run as a subprocess as for <tt><font size=+1>r</font></tt>. In this case no
note can be sent; the remainder of the line is
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treated as arguments to the subprocess.<br>
</table>
<tt><font size=+1>S</font></tt><i>s</i> Identical to <tt><font size=+1>s</font></tt> except the subprocess is single stepped for <i>count</i>
lines of C source. In optimized code, the correspondence between
C source and the machine instructions is approximate at best.<br>
<tt><font size=+1>x</font></tt> The current subprocess, if any, is released by <i>db</i> and allowed
to continue executing normally.<br>
<tt><font size=+1>k</font></tt> The current subprocess, if any, is terminated.<br>
<tt><font size=+1>n</font></tt><i>c</i> Display the pending notes for the process. If <i>c</i> is specified,
first delete <i>c’th</i> pending note.<br>
</table>
<p><font size=+1><b>Addresses </b></font><br>
The location in a file or memory image associated with an address
is calculated from a map associated with the file. Each map contains
one or more quadruples (<i>t, f, b, e, o</i>), defining a segment named
<i>t</i> (usually, <i>text</i>, <i>data</i>, or <i>core</i>) in file <i>f</i> mapping addresses in
the range <i>b</i> through <i>e</i> to the part of the file beginning at
offset <i>o</i>. If segments overlap, later segments obscure earlier
ones. An address <i>a</i> is translated to a file address by finding
the last segment in the list for which <i>b</i>≤<i>a</i><<i>e</i>; the location in the
file is then <i>address</i>+<i>f</i>–<i>b</i>.
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Usually, the text and initialized data of a program are mapped
by segments called <i>text</i>, <i>data</i>, and <i>bss</i>. Since a program file does
not contain stack data, this data is not mapped. The text segment
is mapped similarly in a normal (i.e., non-kernel) <i>memfile</i>. However,
one or more segments called <i>data</i> provide access to
process memory. This region contains the program’s static data,
the bss, the heap and the stack.
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Sometimes it is useful to define a map with a single segment mapping
the region from 0 to 0xFFFFFFFF; a map of this type allows an
entire file to be examined without address translation.
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The <tt><font size=+1>$m</font></tt> command dumps the currently active maps. The <tt><font size=+1>?m</font></tt> and <tt><font size=+1>/m</font></tt>
commands modify the segment parameters in the <i>textfile</i> and <i>memfile</i>
maps, respectively.<br>
</table>
<p><font size=+1><b>EXAMPLES </b></font><br>
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To set a breakpoint at the beginning of <tt><font size=+1>write()</font></tt> in extant process
27:<br>
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<tt><font size=+1>% db 27<br>
:h<br>
write:b<br>
:c<br>
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</font></tt>
</table>
To set a breakpoint at the entry of function <tt><font size=+1>parse</font></tt> when the local
variable <tt><font size=+1>argc</font></tt> in <tt><font size=+1>main</font></tt> is equal to 1:<br>
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<tt><font size=+1>parse:b *main.argc−1=X<br>
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</font></tt>
</table>
This prints the value of <tt><font size=+1>argc−1</font></tt> which as a side effect sets dot;
when <tt><font size=+1>argc</font></tt> is one the breakpoint will fire. Beware that local variables
may be stored in registers; see the BUGS section.<br>
</table>
<p><font size=+1><b>SEE ALSO </b></font><br>
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<a href="../man1/acid.html"><i>acid</i>(1)</a><br>
</table>
<p><font size=+1><b>SOURCE </b></font><br>
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<tt><font size=+1>/usr/local/plan9/src/cmd/db<br>
</font></tt>
</table>
<p><font size=+1><b>DIAGNOSTICS </b></font><br>
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Exit status is 0, unless the last command failed or returned non-zero
status.<br>
</table>
<p><font size=+1><b>BUGS </b></font><br>
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Examining a local variable with <i>routine.name</i> returns the contents
of the memory allocated for the variable, but with optimization,
variables often reside in registers. Also, on some architectures,
the first argument is always passed in a register.
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Variables and parameters that have been optimized away do not
appear in the symbol table, returning the error <i>bad local variable</i>
when accessed by <i>db</i>.
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Breakpoints should not be set on instructions scheduled in delay
slots. When a program stops on such a breakpoint, it is usually
impossible to continue its execution.<br>
</table>
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</table>
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