.TH ACID 1
.SH NAME
acid, truss, trump \- debugger
.SH SYNOPSIS
.B acid
[
.BI -l " libfile
]
[
.B -wq
] [
.B -m
.I machine
] [
.I pid
]
[
.I textfile
]
.PP
.B acid
.B -l
.B truss
.I textfile
.PP
.B acid
.B -l
.B trump
[
.I pid
]
[
.I textfile
]
.SH DESCRIPTION
.I Acid
is a programmable symbolic debugger.
It can inspect one or more processes that share an address space.
A program to be debugged may be specified by the process id of
a running or defunct process,
or by the name of the program's text file 
.RB ( 8.out
by default).
At the prompt,
.I acid
will store function definitions or print the value of expressions.
Options are
.TP .9i
.B -w
Allow the textfile to be modified.
.TP
.B -q
Print variable renamings at startup.
.TP
.BI -l " library
Load from 
.I library
at startup; see below.
.TP
.BI -m " machine
Assume instructions are for the given CPU type
(one of
.BR alpha ,
.BR 386 ,
etc., as listed in
.IR 2c (1),
or
.B sunsparc
or
.B mipsco
for the  manufacturer-defined instruction notation for those processors)
instead of using the magic number to select
the CPU type.
.TP
.BI -k
Debug the kernel state for the process, rather than the user state.
.PP
At startup,
.I acid
obtains standard function definitions from the library file
.BR /sys/lib/acid/port ,
architecture-dependent functions from
.BR /sys/lib/acid/$objtype ,
user-specified functions from
.BR $home/lib/acid ,
and further functions from 
.B -l
files.
Definitions in any file may override previously defined functions.
If the function
.IR acidinit ()
is defined, it will be invoked after all modules have been loaded.
See
.IR 2c (1)
for information about creating
.I acid
functions for examining data structures.
.SS Language
Symbols of the program being debugged become integer 
variables whose values are addresses.
Contents of addresses are obtained by indirection.
Local variables are qualified by
function name, for example
.BR main:argv .
When program symbols conflict with
.I acid
words, distinguishing 
.B $
signs are prefixed.
Such renamings are reported at startup if the option
.B -q
is enabled.
.PP
Variable types
.RI ( "integer, float, list, string" )
and formats are inferred from assignments.
Truth values false/true are attributed to zero/nonzero
integers or floats and to empty/nonempty lists or strings.
Lists are sequences of expressions surrounded by
.BR {\^} 
and separated by commas.
.PP
Expressions are much as in C,
but yield both a value and a format.
Casts to complex types are allowed.
Lists admit the following operators, with
subscripts counted from 0.
.IP
.BI head " list
.br
.BI tail " list
.br
.BI append " list", " element
.br
.BI delete " list", " subscript
.PP
Format codes are the same as in
.IR db (1).
Formats may be attached to (unary) expressions with
.BR \e ,
e.g.
.BR (32*7)\eD .
There are two indirection operators,
.B *
to address a core image,
.B @
to address a text file.
The type and format of the result are determined by the format of the operand,
whose type must be integer.
.PP
Statements are
.IP
.BI if " expr " then " statement " "\fR[ \fPelse\fI statement \fR]
.br
.BI while " expr " do " statement
.br
.BI loop " expr" , " expr " do " statement
.br
.BI defn " name" ( args ") {" " statement \fP}
.br
.BI defn " name"
.br
.IB name ( args )
.br
.BI builtin " name" ( args )
.br
.BI local " name
.br
.BI return " expr
.br
.BR whatis " [ \fI name \fP]
.PP
The statement
.B defn
.I name
clears the definition for
.IR name .
A
.B defn
may override a built-in function;
prefixing a function call with
.B builtin
ignores any overriding
.BR defn ,
forcing the use of the built-in function.
.PP
Here is a partial list of functions; see the manual for a complete list.
.TF asm(address)
.TP
.B stk()
Print a stack trace for current process.
.TP
.B lstk()
Print a stack trace with values of local variables.
.TP
.B gpr()
Print general registers.
Registers can also be accessed by name, for example
.BR *R0 .
.TP
.B spr()
Print special registers such as program counter and stack pointer.
.TP
.B fpr()
Print floating-point registers.
.TP
.B regs()
Same as
.BR spr();gpr() .
.TP
.BI fmt( expr , format )
Expression 
.I expr
with format given by the character value of expression
.IR format .
.TP
.BI src( address )
Print 10 lines of source around the program address.
.TP
.BI Bsrc( address )
Get the source line for the program address
into a window of a running
.IR sam (1)
and select it.
.TP
.BI line( address )
Print source line nearest to the program address.
.TP
.B source()
List current source directories.
.TP
.BI addsrcdir( string )
Add a source directory to the list.
.TP
.BI filepc( where )
Convert a string of the form 
.IB sourcefile : linenumber
to a machine address.
.TP
.BI pcfile( address )
Convert a machine address to a source file name.
.TP
.BI pcline( address )
Convert a machine address to a source line number.
.TP
.BI bptab()
List breakpoints set in the current process.
.TP
.BI bpset( address )
Set a breakpoint in the current process at the given address.
.TP
.BI bpdel( address )
Delete a breakpoint from the current process.
.TP
.B cont()
Continue execution of current process and wait for it to stop.
.TP
.B step()
Execute a single machine instruction in the current process.
.TP
.B func()
Step repeatedly until after a function return.
.TP
.BI stopped( pid )
This replaceable function is called automatically when the given process
stops.
It normally prints the program counter and returns to the prompt.
.TP
.BI asm( address )
Disassemble 30 machine instructions beginning at the given address.
.TP
.BI mem( address , string )
Print a block of memory
interpreted according to a string of format codes.
.TP
.BI dump( address , n , string\fP)
Like
.BR mem (),
repeated for 
.I n
consecutive blocks.
.TP
.BI print( expr , ... )
Print the values of the expressions.
.TP
.BI newproc( arguments )
Start a new process with arguments given as a string
and halt at the first instruction.
.TP
.B new()
Like 
.IR newproc (),
but take arguments (except
.BR argv[0] )
from string variable
.BR progargs .
.TP
.B win()
Like 
.IR new (),
but run the process in a separate window.
.TP
.BI start( pid )
Start a stopped process.
.TP
.BI kill( pid )
Kill the given process.
.TP
.BI setproc( pid )
Make the given process current.
.TP
.BI rc( string )
Escape to the shell,
.IR rc (1),
to execute the command string.
.SS Libraries
There are a number of
.I acid
`libraries' that provide higher-level debugging facilities.  Two notable
examples are
.I truss
and
.IR trump ,
which use
.I acid
to trace system calls
.RI ( truss )
and memory allocation
.RI ( trump ).
Both require starting
.I acid
on the program, either by attaching to a running process or by
executing
.B new()
on a binary (perhaps after setting
.BR progargs ),
stopping the process, and then running
.B truss()
or
.B trump()
to execute the program under the scaffolding.
The output will be a trace of the system calls
.RI ( truss )
or memory allocation and free calls
.RI ( trump )
executed by the program.
When finished tracing, stop the process and execute
.B untruss()
or
.B untrump()
followed by
.B cont()
to resume execution.
.SH EXAMPLES
Start to debug
.BR /bin/ls ;
set some breakpoints; run up to the first one:
.IP
.EX
% acid /bin/ls
/bin/ls: mips plan 9 executable
/sys/lib/acid/port
/sys/lib/acid/mips
acid: new()
70094: system call	_main	ADD	$-0x14,R29
70094: breakpoint	main+0x4	MOVW	R31,0x0(R29)
acid: pid
70094
acid: argv0 = **main:argv\es
acid: whatis argv0
integer variable format s
acid: *argv0
/bin/ls
acid: bpset(ls)
acid: cont()
70094: breakpoint  ls	ADD	$-0x16c8,R29
acid: 
.EE
.PP
Display elements of a linked list of structures:
.IP
.EX
complex Str { 'D' 0 val; 'X' 4 next; };
complex Str s;
s = *headstr;
while s != 0 do{
	print(s.val, "\en");
	s = s.next;
}
.EE
.PP
Note the use of the
.B .
operator instead of
.BR -> .
.PP
Display an array of bytes declared in C as
.BR "char array[]" .
.IP
.EX
*(array\es)
.EE
.PP
This example gives
.B array
string format, then prints the string beginning at the address (in
.I acid
notation)
.BR *array .
.PP
Trace the system calls executed by
.IR ls (1):
.IP
.EX
% acid -l truss /bin/ls
/bin/ls:386 plan 9 executable

/sys/lib/acid/port
/sys/lib/acid/kernel
/sys/lib/acid/truss
/sys/lib/acid/386
acid: progargs = "-l lib/profile"
acid: new()
acid: truss()
open("#c/pid", 0)
	return value: 3
pread(3, 0x7fffeeac, 20, -1)
	return value: 12
	data: "        166 "
\&...
stat("lib/profile", 0x0000f8cc, 113)
	return value: 65
open("/env/timezone", 0)
	return value: 3
pread(3, 0x7fffd7c4, 1680, -1)
	return value: 1518
	data: "EST -18000 EDT -14400
   9943200   25664400   41392800   57718800   73447200   89168400
 104896800  ..."
close(3)
	return value: 0
pwrite(1, "--rw-rw-r-- M 9 rob rob 2519 Mar 22 10:29 lib/profile
", 54, -1)
--rw-rw-r-- M 9 rob rob 2519 Mar 22 10:29 lib/profile
	return value: 54
\&...
166: breakpoint	_exits+0x5	INTB	$0x40
acid: cont()
.EE
.SH FILES
.B /proc/*/text
.br
.B /proc/*/mem
.br
.B /proc/*/ctl
.br
.B /proc/*/note
.br
.B /sys/lib/acid/$objtype
.br
.B /sys/lib/acid/port
.br
.B /sys/lib/acid/kernel
.br
.B /sys/lib/acid/trump
.br
.B /sys/lib/acid/truss
.br
.B $home/lib/acid
.SH SOURCE
.B /sys/src/cmd/acid
.SH "SEE ALSO"
.IR 2a (1),
.IR 2c (1),
.IR 2l (1),
.IR mk (1),
.IR db (1)
.br
Phil Winterbottom,
``Acid Manual''.
.SH DIAGNOSTICS
At termination, kill commands are proposed
for processes that are still active.
.SH BUGS
There is no way to redirect the standard input and standard output
of a new process.
.br
Source line selection near the beginning of a file may pick
an adjacent file.
.br
With the extant stepping commands, one cannot step through instructions
outside the text segment and it is hard to debug across process forks.