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acid - debugger


acid [ -l libfile ] [ -wq ] [ -m machine ] [ pid ] [ textfile ]


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 (v.out by default). At the prompt, acid will store function definitions or print the value of expressions. Options are

Allow the textfile to be modified.
Don't 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 386, 86, 68020, 960, power, arm, mips, mipsco, sparc, or sunsparc) instead of using the magic number to select the CPU type.

At startup, acid obtains standard function definitions from the library file /lib/acid/port, architecture-dependent functions from /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 modules have been loaded. See 2c(10.1) for information about creating acid functions for examining data structures.

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; option -q suppresses them.

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(10.1). 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 }
local name
return expr
whatis [ name ]

Here is a partial list of functions; see the manual for a complete list.

Print a stack trace for current process.
Print a stack trace with values of local variables.
Print general registers. Registers can also be accessed by name, for example *R0.
Print special registers such as program counter and stack pointer.
Print floating-point registers.
Same as spr();gpr().
Expression expr with format given by the character value of expression format.
Print 10 lines of source around the program address.
Get the source line for the program address into a window of a running editor and select it. (This works only on Plan 9, or a Unix-like system running `Plan 9 Ports'.)
Print source line nearest to the program address.
List current source directories.
Add a source directory to the list.
Convert a string of the form sourcefile:linenumber to a machine address.
Convert a machine address to a source file name.
Convert a machine address to a source line number.
List breakpoints set in the current process.
Set a breakpoint in the current process at the given address.
Delete a breakpoint from the current process.
Continue execution of current process and wait for it to stop.
Execute a single machine instruction in the current process.
Step repeatedly until after a function return.
This replaceable function is called automatically when the given process stops. It normally prints the program counter and returns to the prompt.
Disassemble 30 machine instructions beginning at the given address.
Print a block of memory interpreted according to a string of format codes.
Like mem(), repeated for n consecutive blocks.
Print the values of the expressions.
Start a new process with arguments given as a string and halt at the first instruction.
Like newproc(), but take arguments (except argv[0]) from string variable progargs.
Like new(), but run the process in a separate window.
Start a stopped process.
Kill the given process.
Make the given process current.
Escape to the shell, to execute the command string.


Start to debug /bin/ls; set some breakpoints; run up to the first one:

% acid /bin/ls
/bin/ls: mips plan 9 executable
acid: new()
70094: system call  _main       ADD     $-0x14,R29
70094: breakpoint   main+0x4    MOVW    R31,0x0(R29)
acid: pid
acid: argv0 = **main:argv\s
acid: whatis argv0
integer variable format s
acid: *argv0
acid: bpset(ls)
acid: cont()
70094: breakpoint  ls   ADD $-0x16c8,R29

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[].


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






2a(10.1), 2c(10.1), 2l(10.1), mk(10.1), db(10.1)
Phil Winterbottom, ``Acid Manual''.


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


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.

ACID(10.1 ) Rev:  Tue Mar 31 02:42:39 GMT 2015