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NAME
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acid, acidtypes – debugger
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SYNOPSIS
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acid [ −l library ] [ −wq ] [ −m machine ] [ pid | core ] [ textfile
]
acidtypes [ −p prefix ] file ...
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DESCRIPTION
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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 (a.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 (see
mach(3)) instead of using the executable header 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 /usr/local/plan9/acid/port, architecture-dependent
functions from /usr/local/plan9/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. Then the function acidmap() will be invoked if defined.
/usr/local/plan9/acid/port provides a definition of acidmap that
attaches all the shared libraries being used by the target process
and then runs acidtypes (q.v.) to create 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;
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.
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head list
tail list
append list, element
delete list, subscript
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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
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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 ]
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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)
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Expression expr with format given by the character value of expression
format.
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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)
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Add a source directory to the list.
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filepc(where)Convert a string of the form sourcefile:linenumber
to a machine address.
pcfile(address)
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Convert a machine address to a source file name.
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pcline(address)
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Convert a machine address to a source line number.
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bptab() List breakpoints set in the current process.
bpset(address)Set a breakpoint in the current process at the given
address. (Doesn’t work on Unix yet.)
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.
(Doesn’t work on Unix yet.)
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)
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Print a block of memory interpreted according to a string of format
codes.
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dump(address,n,string)
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Like mem(), repeated for n consecutive blocks.
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print(expr,...)Print the values of the expressions.
newproc(arguments)
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Start a new process with arguments given as a string and halt
at the first instruction.
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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.
include(string)Read acid commands from the named file.
includepipe(string)
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Run the command string, reading its standard output as acid commands.
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Shared library segments
When a pid or core file is specified on the command line, acid
will, as part of its startup, determine the set of shared libraries
in use by the process image and map those at appropriate locations.
If acid is started without a pid or core file and is subsequently
attached to a process via setproc, the shared library maps can
be initialized by calling
dynamicmap().
Type information
Unix compilers conventionally include detailed type information
in the debugging symbol section of binaries. The external program
acidtypes extracts this information and formats it as acid program
text. Once the shared libraries have been mapped, the default
acid startup invokes acidtypes (via includepipe) on the set of
currently mapped text
files. The function acidtypes() can be called to rerun the command
after changing the set of mapped text files.
Acid Libraries
There are a number of acid ‘libraries’ that provide higher-level
debugging facilities. One notable example is trump, which uses
acid to trace memory allocation. Trump requires 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 trump() to execute the program under the scaffolding.
The output will be a trace of the memory allocation and free calls
executed by the program. When finished tracing, stop the process
and execute untrump() followed by cont() to resume execution.
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EXAMPLES
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Start to debug /bin/ls; set some breakpoints; run up to the first
one (this example doesn’t work on Unix yet):
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% 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:
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Display elements of a linked list of structures:
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complex Str { 'D' 0 val; 'X' 4 next; };
s = *headstr;
while s != 0 do{
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complex Str s;
print(s.val, "\n");
s = s.next;
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}
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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.
Trace the system calls executed by ls(1) (neither does this one):
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% 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)
pread(3, 0x7fffeeac, 20, −1)
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return value: 12
data: " 166 "
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...
stat("lib/profile", 0x0000f8cc, 113)
open("/env/timezone", 0)
pread(3, 0x7fffd7c4, 1680, −1)
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return value: 1518
data: "EST −18000 EDT −14400
9943200 25664400 41392800 57718800 73447200 89168400
104896800 ..."
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close(3)
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
...
166: breakpoint _exits+0x5 INTB $0x40
acid: cont()
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FILES
SOURCE
SEE ALSO
DIAGNOSTICS
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At termination, kill commands are proposed for processes that
are still active.
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BUGS
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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.
Breakpoints do not work yet. Therefore, commands such as step,
new, and truss do not work either. New in particular will need
some help to cope with dynamic libraries.
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