NAME
acid, truss, trump – debugger

SYNOPSIS
acid [ –kqw ] [ –l library ] [ –m machine ] [ pid ] [ textfile ]

acid –l truss textfile

acid –l trump [ pid ] [ textfile ]

DESCRIPTION
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 (8.out by default). At the prompt, acid will store function definitions or print the value of expressions. Options are
w         Allow the textfile to be modified.
q         Print variable renamings at startup.
l library    Load from library at startup; see below.
m machine   Assume instructions are for the given CPU type (one of amd64, 386, etc., as listed in 8c(1), or mipsco for the manufacturer–defined instruction notation for those processors) instead of using the magic number to select the CPU type.
k         Debug the kernel state for the process, rather than the user state.

At startup, acid obtains standard function definitions from the library file /sys/lib/acid/port, architecture–dependent functions from /sys/lib/acid/$objtype, user–specified functions from $home/lib/acid, and further functions from –l files. Definitions in any file may override previously defined functions. If the function acidinit() is defined, it will be invoked after all libraries have been loaded. See 8c(1) for information about creating acid functions for examining data structures.

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 main:argv. When program symbols conflict with acid words, distinguishing $ signs are prefixed. Such renamings are reported at startup if the option –q is enabled.

Variable types (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 {} and separated by commas.

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.
head list
tail list
append list, element
delete list, subscript

Format codes are the same as in db(1). Formats may be attached to (unary) expressions with \, e.g. (32*7)\D. There are two indirection operators, * to address a core image, @ 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.

Statements are
if expr then statement [ else statement ]
while expr do statement
loop expr, expr do statement
defn name(args) { statement }
defn
name
name
(args)
builtin
name(args)
local
name
return expr
whatis [ name ]

The statement defn name clears the definition for name. A defn may override a built–in function; prefixing a function call with builtin ignores any overriding defn, forcing the use of the built–in function.

Here is a partial list of functions; see the manual for a complete list.
stk()          Print a stack trace for current process.
lstk()         Print a stack trace with values of local variables.
gpr()          Print general registers. Registers can also be accessed by name, for example *R0.
spr()          Print special registers such as program counter and stack pointer.
fpr()          Print floating–point registers.
regs()         Same as spr();gpr().
fmt(expr,format)
Expression expr with format given by the character value of expression format.
src(address)     Print 10 lines of source around the program address.
Bsrc(address)    Get the source line for the program address into a window of a running sam(1) and select it.
line(address)    Print source line nearest to the program address.
source()       List current source directories.
addsrcdir(string)
Add a source directory to the list.
filepc(where)   Convert a string of the form sourcefile:linenumber to a machine address.
pcfile(address)Convert a machine address to a source file name.
pcline(address)Convert a machine address to a source line number.
bptab()        List breakpoints set in the current process.
bpset(address)   Set a breakpoint in the current process at the given address.
bpdel(address)   Delete a breakpoint from the current process.
cont()         Continue execution of current process and wait for it to stop.
step()         Execute a single machine instruction in the current process.
func()         Step repeatedly until after a function return.
stopped(pid)    This replaceable function is called automatically when the given process stops. It normally prints the program counter and returns to the prompt.
asm(address)     Disassemble 30 machine instructions beginning at the given address.
mem(address,string)
Print a block of memory interpreted according to a string of format codes.
dump(address,n,string)
Like mem(), repeated for n consecutive blocks.
print(expr,...)   Print the values of the expressions.
newproc(arguments)
Start a new process with arguments given as a string and halt at the first instruction.
new()          Like newproc(), but take arguments (except argv[0]) from string variable progargs.
win()          Like new(), but run the process in a separate window.
start(pid)      Start a stopped process.
kill(pid)       Kill the given process.
setproc(pid)    Make the given process current.
rc(string)       Escape to the shell, rc(1), to execute the command string.

Libraries
There are a number of acid `libraries' that provide higher–level debugging facilities. Two notable examples are truss and trump, which use acid to trace system calls (truss) and memory allocation (trump). Both require starting acid on the program, either by attaching to a running process or by executing new() on a binary (perhaps after setting progargs), stopping the process, and then running truss() or trump() to execute the program under the scaffolding. The output will be a trace of the system calls (truss) or memory allocation and free calls (trump) executed by the program. When finished tracing, stop the process and execute untruss() or untrump() followed by cont() to resume execution.

EXAMPLES
Start to debug /bin/ls; set some breakpoints; run up to the first one:
% 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\s
acid: whatis argv0
integer variable format s
acid: *argv0
/bin/ls
acid: bpset(ls)
acid: cont()
70094: breakpoint    ls      ADD    $–0x16c8,R29
acid:

Display elements of a linked list of structures:
complex Str { 'D' 0 val; 'X' 4 next; };
complex Str s;
s = *headstr;
while s != 0 do{
print(s.val, "\n");
s = s.next;
}

Note the use of the . operator instead of –>.

Display an array of bytes declared in C as char array[].
*(array\s)

This example gives array string format, then prints the string beginning at the address (in acid notation) *array.

Trace the system calls executed by ls(1):
% 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()

FILES
/proc/*/text
/proc/*/mem
/proc/*/ctl
/proc/*/note
/sys/lib/acid/$objtype
/sys/lib/acid/port
/sys/lib/acid/kernel
/sys/lib/acid/trump
/sys/lib/acid/truss
$home/lib/acid

SOURCE
/sys/src/cmd/acid

SEE ALSO
8a(1), 8c(1), 8l(1), mk(1), db(1)
Phil Winterbottom, ``Acid Manual''.

DIAGNOSTICS
At termination, kill commands are proposed for processes that are still active.

BUGS
There is no way to redirect the standard input and standard output of a new process.
Source line selection near the beginning of a file may pick an adjacent file.
With the extant stepping commands, one cannot step through instructions outside the text segment and it is hard to debug across process forks.
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