Next: , Previous: Operation, Up: Kernel Debugger

11.2 Commands

examine(x) [/modifier] addr[,count] [ thread ]
Display the addressed locations according to the formats in the modifier. Multiple modifier formats display multiple locations. If no format is specified, the last formats specified for this command is used. Address space other than that of the current thread can be specified with t option in the modifier and thread parameter. The format characters are
look at by bytes(8 bits)
look at by half words(16 bits)
look at by long words(32 bits)
print the location being displayed
skip one unit producing no output
print the location with a line number if possible
display in unsigned hex
display in signed hex
display in unsigned octal
display in signed decimal
display in unsigned decimal
display in current radix, signed
display low 8 bits as a character. Non-printing characters are displayed as an octal escape code (e.g. '\000').
display the null-terminated string at the location. Non-printing characters are displayed as octal escapes.
display in unsigned hex with character dump at the end of each line. The location is also displayed in hex at the beginning of each line.
display as an instruction
display as an instruction with possible alternate formats depending on the machine:
don't assume that each external label is a procedure entry mask
don't round to the next long word boundary
print register contents

Examine forward. It executes an examine command with the last specified parameters to it except that the next address displayed by it is used as the start address.
Examine backward. It executes an examine command with the last specified parameters to it except that the last start address subtracted by the size displayed by it is used as the start address.
print[/axzodurc] addr1 [ addr2 ... ]
Print addr's according to the modifier character. Valid formats are: a x z o d u r c. If no modifier is specified, the last one specified to it is used. addr can be a string, and it is printed as it is. For example,
          print/x "eax = " $eax "\necx = " $ecx "\n"

will print like

          eax = xxxxxx
          ecx = yyyyyy

write[/bhlt] addr [ thread ] expr1 [ expr2 ... ]
Write the expressions at succeeding locations. The write unit size can be specified in the modifier with a letter b (byte), h (half word) or l(long word) respectively. If omitted, long word is assumed. Target address space can also be specified with t option in the modifier and thread parameter. Warning: since there is no delimiter between expressions, strange things may happen. It's best to enclose each expression in parentheses.
set $variable [=] expr
Set the named variable or register with the value of expr. Valid variable names are described below.
break[/tuTU] addr[,count] [ thread1 ... ]
Set a break point at addr. If count is supplied, continues (count-1) times before stopping at the break point. If the break point is set, a break point number is printed with ‘#’. This number can be used in deleting the break point or adding conditions to it.
Set a break point only for a specific thread. The thread is specified by thread parameter, or default one is used if the parameter is omitted.
Set a break point in user space address. It may be combined with t or T option to specify the non-current target user space. Without u option, the address is considered in the kernel space, and wrong space address is rejected with an error message. This option can be used only if it is supported by machine dependent routines.
Set a break point only for threads in a specific task. It is like t option except that the break point is valid for all threads which belong to the same task as the specified target thread.
Set a break point in shared user space address. It is like u option, except that the break point is valid for all threads which share the same address space even if t option is specified. t option is used only to specify the target shared space. Without t option, u and U have the same meanings. U is useful for setting a user space break point in non-current address space with t option such as in an emulation library space. This option can be used only if it is supported by machine dependent routines.

Warning: if a user text is shadowed by a normal user space debugger, user space break points may not work correctly. Setting a break point at the low-level code paths may also cause strange behavior.

delete[/tuTU] addr|#number [ thread1 ... ]
Delete the break point. The target break point can be specified by a break point number with #, or by addr like specified in break command.
cond #number [ condition commands ]
Set or delete a condition for the break point specified by the number. If the condition and commands are null, the condition is deleted. Otherwise the condition is set for it. When the break point is hit, the condition is evaluated. The commands will be executed if the condition is true and the break point count set by a break point command becomes zero. commands is a list of commands separated by semicolons. Each command in the list is executed in that order, but if a continue command is executed, the command execution stops there, and the stopped thread resumes execution. If the command execution reaches the end of the list, and it enters into a command input mode. For example,
          set $work0 0
          break/Tu xxx_start $task7.0
          cond #1  (1)  set $work0 1; set $work1 0; cont
          break/T  vm_fault $task7.0
          cond #2  ($work0) set $work1 ($work1+1); cont
          break/Tu xxx_end $task7.0
          cond #3  ($work0) print $work1 " faults\n"; set $work0 0

will print page fault counts from xxx_start to xxx_end in task7.

step[/p] [,count]
Single step count times. If p option is specified, print each instruction at each step. Otherwise, only print the last instruction.

Warning: depending on machine type, it may not be possible to single-step through some low-level code paths or user space code. On machines with software-emulated single-stepping (e.g., pmax), stepping through code executed by interrupt handlers will probably do the wrong thing.

Continue execution until a breakpoint or watchpoint. If /c, count instructions while executing. Some machines (e.g., pmax) also count loads and stores.

Warning: when counting, the debugger is really silently single-stepping. This means that single-stepping on low-level code may cause strange behavior.

Stop at the next call or return instruction.
Stop at the matching return instruction. If p option is specified, print the call nesting depth and the cumulative instruction count at each call or return. Otherwise, only print when the matching return is hit.
A synonym for next.
trace[/tu] [ frame_addr|thread ][,count]
Stack trace. u option traces user space; if omitted, only traces kernel space. If t option is specified, it shows the stack trace of the specified thread or a default target thread. Otherwise, it shows the stack trace of the current thread from the frame address specified by a parameter or from the current frame. count is the number of frames to be traced. If the count is omitted, all frames are printed.

Warning: If the target thread's stack is not in the main memory at that time, the stack trace will fail. User space stack trace is valid only if the machine dependent code supports it.

search[/bhl] addr value [mask] [,count]
Search memory for a value. This command might fail in interesting ways if it doesn't find the searched-for value. This is because ddb doesn't always recover from touching bad memory. The optional count argument limits the search.
macro name commands
Define a debugger macro as name. commands is a list of commands to be associated with the macro. In the expressions of the command list, a variable $argxx can be used to get a parameter passed to the macro. When a macro is called, each argument is evaluated as an expression, and the value is assigned to each parameter, $arg1, $arg2, ... respectively. 10 $arg variables are reserved to each level of macros, and they can be used as local variables. The nesting of macro can be allowed up to 5 levels. For example,
          macro xinit set $work0 $arg1
          macro xlist examine/m $work0,4; set $work0 *($work0)
          xinit *(xxx_list)

will print the contents of a list starting from xxx_list by each xlist command.

dmacro name
Delete the macro named name.
show all threads[/ul]
Display all tasks and threads information. This version of ddb prints more information than previous one. It shows UNIX process information like ps for each task. The UNIX process information may not be shown if it is not supported in the machine, or the bottom of the stack of the target task is not in the main memory at that time. It also shows task and thread identification numbers. These numbers can be used to specify a task or a thread symbolically in various commands. The numbers are valid only in the same debugger session. If the execution is resumed again, the numbers may change. The current thread can be distinguished from others by a # after the thread id instead of :. Without l option, it only shows thread id, thread structure address and the status for each thread. The status consists of 5 letters, R(run), W(wait), S(suspended), O(swapped out) and N(interruptible), and if corresponding status bit is off, . is printed instead. If l option is specified, more detail information is printed for each thread.
show task [ addr ]
Display the information of a task specified by addr. If addr is omitted, current task information is displayed.
show thread [ addr ]
Display the information of a thread specified by addr. If addr is omitted, current thread information is displayed.
show registers[/tu [ thread ]]
Display the register set. Target thread can be specified with t option and thread parameter. If u option is specified, it displays user registers instead of kernel or currently saved one.

Warning: The support of t and u option depends on the machine. If not supported, incorrect information will be displayed.

show map addr
Prints the vm_map at addr.
show object addr
Prints the vm_object at addr.
show page addr
Prints the vm_page structure at addr.
show port addr
Prints the ipc_port structure at addr.
show ipc_port[/t [ thread ]]
Prints all ipc_port structure's addresses the target thread has. The target thread is a current thread or that specified by a parameter.
show macro [ name ]
Show the definitions of macros. If name is specified, only the definition of it is displayed. Otherwise, definitions of all macros are displayed.
show watches
Displays all watchpoints.
watch[/T] addr,size [ task ]
Set a watchpoint for a region. Execution stops when an attempt to modify the region occurs. The size argument defaults to 4. Without T option, addr is assumed to be a kernel address. If you want to set a watch point in user space, specify T and task parameter where the address belongs to. If the task parameter is omitted, a task of the default target thread or a current task is assumed. If you specify a wrong space address, the request is rejected with an error message.

Warning: Attempts to watch wired kernel memory may cause unrecoverable error in some systems such as i386. Watchpoints on user addresses work best.