.\" .\" Mach Operating System .\" Copyright (c) 1991,1990 Carnegie Mellon University .\" All Rights Reserved. .\" .\" Permission to use, copy, modify and distribute this software and its .\" documentation is hereby granted, provided that both the copyright .\" notice and this permission notice appear in all copies of the .\" software, derivative works or modified versions, and any portions .\" thereof, and that both notices appear in supporting documentation. .\" .\" CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" .\" CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR .\" ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. .\" .\" Carnegie Mellon requests users of this software to return to .\" .\" Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU .\" School of Computer Science .\" Carnegie Mellon University .\" Pittsburgh PA 15213-3890 .\" .\" any improvements or extensions that they make and grant Carnegie Mellon .\" the rights to redistribute these changes. .\" .\" changed a \# to #, since groff choked on it. .\" .\" HISTORY .\" ddb.4,v .\" Revision 1.1 1993/07/15 18:41:02 brezak .\" Man page for DDB .\" .\" Revision 2.6 92/04/08 08:52:57 rpd .\" Changes from OSF. .\" [92/01/17 14:19:22 jsb] .\" Changes for OSF debugger modifications. .\" [91/12/12 tak] .\" .\" Revision 2.5 91/06/25 13:50:22 rpd .\" Added some watchpoint explanation. .\" [91/06/25 rpd] .\" .\" Revision 2.4 91/06/17 15:47:31 jsb .\" Added documentation for continue/c, match, search, and watchpoints. .\" I've not actually explained what a watchpoint is; maybe Rich can .\" do that (hint, hint). .\" [91/06/17 10:58:08 jsb] .\" .\" Revision 2.3 91/05/14 17:04:23 mrt .\" Correcting copyright .\" .\" Revision 2.2 91/02/14 14:10:06 mrt .\" Changed to new Mach copyright .\" [91/02/12 18:10:12 mrt] .\" .\" Revision 2.2 90/08/30 14:23:15 dbg .\" Created. .\" [90/08/30 dbg] .\" .\" $FreeBSD: src/share/man/man4/ddb.4,v 1.7.2.6 2001/08/17 13:08:37 ru Exp $ .\" .Dd June 21, 2020 .Dt DDB 4 .Os .Sh NAME .Nm ddb .Nd interactive kernel debugger .Sh SYNOPSIS .Cd options DDB .Pp .Cd options DDB_TRACE .Cd options DDB_UNATTENDED .Sh DESCRIPTION The .Nm kernel debugger has most of the features of the old kdb, but with a more rational syntax inspired by .Xr gdb 1 . If linked into the running kernel, it can be invoked locally with the .Ql debug .Xr keymap 5 action (the default is Control-Alt-Esc). The debugger is also invoked on kernel .Xr panic 9 if the .Va debug.debugger_on_panic .Xr sysctl 8 MIB variable is set non-zero, which is the default unless the .Dv DDB_UNATTENDED option is specified. If set, the .Va debug.trace_on_panic .Xr sysctl 8 MIB variable will cause .Nm to print a stack trace on .Xr panic 9 . It is zero by default unless the .Dv DDB_TRACE option is specified. .Pp The current location is called `dot'. The `dot' is displayed with a hexadecimal format at a prompt. Examine and write commands update `dot' to the address of the last line examined or the last location modified, and set `next' to the address of the next location to be examined or changed. Other commands don't change `dot', and set `next' to be the same as `dot'. .Pp The general command syntax is: .Cm command Ns Op Li \&/ Ns Ar modifier .Ar address Ns Op Li , Ns Ar count .Pp A blank line repeats the previous command from the address `next' with count 1 and no modifiers. Specifying .Ar address sets `dot' to the address. Omitting .Ar address uses `dot'. A missing .Ar count is taken to be 1 for printing commands or infinity for stack traces. .Pp The .Nm debugger has a feature like the .Xr more 1 command for the output. If an output line exceeds the number set in the .Li \&$lines variable, it displays .Dq Em --db_more-- and waits for a response. The valid responses for it are: .Pp .Bl -tag -compact -width SPC .It Li SPC one more page .It Li RET one more line .It Li q abort the current command, and return to the command input mode .El .Pp Finally, .Nm provides a small (currently 10 items) command history, and offers simple emacs-style command line editing capabilities. In addition to the emacs control keys, the usual ANSI arrow keys might be used to browse through the history buffer, and move the cursor within the current line. .Sh COMMANDS .Bl -ohang .It Xo .Cm examine or .Cm x .Xc 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. .Pp The format characters are: .Bl -tag -compact -width indent .It Li b look at by bytes (8 bits) .It Li h look at by half words (16 bits) .It Li l look at by long words (32 bits) .It Li a print the location being displayed .It Li A print the location with a line number if possible .It Li x display in unsigned hex .It Li z display in signed hex .It Li o display in unsigned octal .It Li d display in signed decimal .It Li u display in unsigned decimal .It Li r display in current radix, signed .It Li c display low 8 bits as a character. Non-printing characters are displayed as an octal escape code (e.g., `\e000'). .It Li s display the null-terminated string at the location. Non-printing characters are displayed as octal escapes. .It Li m 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. .It Li i display as an instruction .It Li I alias for .Li i .El .It Cm xf Examine forward: Execute an examine command with the last specified parameters to it except that the next address displayed by it is used as the start address. .It Cm xb Examine backward: Execute 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. .It Xo .Cm print .Op Cm /acdoruxz or .Cm p .Op Cm /acdoruxz .Xc Print .Ar addr Ns s according to the modifier character (as described above for .Li examine ) . Valid formats are: .Li a , .Li x , .Li z , .Li o , .Li d , .Li u , .Li r , and .Li c . If no modifier is specified, the last one specified to it is used. .Ar addr can be a string, in which case it is printed as it is. For example: .Bd -literal -offset indent print/x \&"eax = \&" $eax \&"\enecx = \&" $ecx \&"\en\&" .Ed .Pp will print like: .Bd -literal -offset indent eax = xxxxxx ecx = yyyyyy .Ed .It Xo .Cm write .Op Cm /bhl .Ar addr .Ar expr1 .Op Ar "expr2 ..." or .Cm w .Op Cm /bhl .Ar addr .Ar expr1 .Op Ar "expr2 ..." .Xc Write the expressions specified after .Ar addr on the command line at succeeding locations starting with .Ar addr The write unit size can be specified in the modifier with a letter .Li b (byte), .Li h (half word) or .Li l (long word) respectively. If omitted, long word is assumed. .Pp .Sy Warning : since there is no delimiter between expressions, strange things may happen. It's best to enclose each expression in parentheses. .It Xo .Cm set .Li \&$ Ns Ar variable .Op Li = .Ar expr .Xc Set the named variable or register with the value of .Ar expr . Valid variable names are described below. .It Cm break Ns Op Cm /u Set a break point at .Ar addr . If .Ar count is supplied, continues .Ar count - 1 times before stopping at the break point. If the break point is set, a break point number is printed with .Sq Li \&# . This number can be used in deleting the break point or adding conditions to it. .Pp If the .Li u modifier is specified, this command sets a break point in user space address. Without the .Li u option, the address is considered in the kernel space, and wrong space address is rejected with an error message. This modifier can be used only if it is supported by machine dependent routines. .Pp .Sy 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. .It Cm delete Xo .Ar addr or .Cm delete Li \&# Ns Ar number or .Cm d Ar addr or .Cm d Li \&# Ns Ar number .Xc Delete the break point. The target break point can be specified by a break point number with .Li # , or by using the same .Ar addr specified in the original .Cm break command. .It Xo .Cm step Ns Op Cm /p or .Cm s Ns Op Cm /p .Xc Single step .Ar count times (the comma is a mandatory part of the syntax). If the .Li p modifier is specified, print each instruction at each step. Otherwise, only print the last instruction. .Pp .Sy 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. .It Xo .Cm continue Ns Op Cm /c or .Cm c Ns Op Cm /c .Xc Continue execution until a breakpoint or watchpoint. If the .Li c modifier is specified, count instructions while executing. Some machines (e.g., pmax) also count loads and stores. .Pp .Sy Warning : when counting, the debugger is really silently single-stepping. This means that single-stepping on low-level code may cause strange behavior. .It Cm until Ns Op Cm /p Stop at the next call or return instruction. If the .Li p modifier 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. .It Xo .Cm next Ns Op Cm /p or .Cm match Ns Op Cm /p .Xc Stop at the matching return instruction. If the .Li p modifier 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. .It Cm call Ar function Call kernel .Ar function . Could be used for kernel dump with .Cm call .Ar dumpsys . .It Cm i Issue a .Fn cpu_invltlb on the current CPU. Useful when testing MMU/PMAP. .It Cm reset Reset the system. .It Xo .Cm trace Ns Op Cm /u .Op Ar frame .Op , Ns Ar count or .Cm where Ns Op Cm /u .Op Ar frame .Op , Ns Ar count .Xc Stack trace. The .Li u option traces user space; if omitted, .Cm trace only traces kernel space. .Ar count is the number of frames to be traced. If .Ar count is omitted, all frames are printed. .Pp .Sy Warning : User space stack trace is valid only if the machine dependent code supports it. .It Xo .Cm search Ns Op Cm /bhl .Ar addr .Ar value .Op Ar mask .Op , Ns Ar count .Xc Search memory for .Ar 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 .Ar count argument limits the search. .It Xo .Cm show all procs Ns Op Cm /m or .Cm ps Ns Op Cm /m .Xc Display all process information. The process information may not be shown if it is not supported in the machine, or the bottom of the stack of the target process is not in the main memory at that time. The .Li m modifier will alter the display to show VM map addresses for the process and not show other info. .It Cm show registers Ns Op Cm /u Display the register set. If the .Li u option is specified, it displays user registers instead of kernel or currently saved one. .Pp .Sy Warning : The support of the .Li u modifier depends on the machine. If not supported, incorrect information will be displayed. .It Xo .Cm show map Ns Op Cm /f .Ar addr .Xc Prints the VM map at .Ar addr . If the .Li f modifier is specified the complete map is printed. .It Xo .Cm show object Ns Op Cm /f .Ar addr .Xc Prints the VM object at .Ar addr . If the .Li f option is specified the complete object is printed. .It Cm show ktr Ns Op Cm /v Prints the contents of .Xr ktr 4 buffer. If the .Li v modifier is specified, timestamp, filename and line number are displayed with each log entry. .It Cm "show tokens" For every global token, it prints its address, exclusive owner address, number of collisions and description. .It Cm "show watches" Displays all watchpoints. .It Xo .Cm watch .Ar addr Ns Op Li \&, Ns Ar size .Xc Set a watchpoint for a region. Execution stops when an attempt to modify the region occurs. The .Ar size argument defaults to 4. If you specify a wrong space address, the request is rejected with an error message. .Pp .Sy Warning : Attempts to watch wired kernel memory may cause unrecoverable error in some systems. Watchpoints on user addresses work best. .It Cm dwatch Ar addr Delete a watchpoint around .Ar addr . .It Cm hwatch Ar addr Ns Op Li \&, Ns Ar size Set a hardware watchpoint for a region. .Ar size defaults to 4. Works like .Cm watch but is much faster. Requires hardware support. You can only have a couple of active hardware watchpoints at a time depending on your hardware. .It Cm dhwatch Ar addr Ns Op Li \&, Ns Ar size Delete a hardware watchpoint that monitors the specified memory range. For a watchpoint to be deleted the provided memory range must be completely within the monitored memory range. .Ar size defaults to 4. .It Cm acpidb If the kernel was compiled with .Dv ACPI_DEBUG , call the ACPICA debugger. For more information, see the .Dq ACPI Component Architecture User Guide and Programmer Reference . .It Cm gdb Toggles between remote GDB and DDB mode. In remote GDB mode, another machine is required that runs .Xr gdb 1 using the remote debug feature, with a connection to the serial console port on the target machine. Currently only available on the .Em i386 architecture. .It Cm help Print a short summary of the available commands and command abbreviations. .El .Sh VARIABLES The debugger accesses registers and variables as .Li \&$ Ns Em name . Register names are as in the .Dq Cm show registers command. Some variables are suffixed with numbers, and may have some modifier following a colon immediately after the variable name. For example, register variables can have a .Li u modifier to indicate user register (e.g., .Li $eax:u ) . .Pp Built-in variables currently supported are: .Bl -tag -width tabstops -compact .It Li radix Input and output radix .It Li maxoff Addresses are printed as 'symbol'+offset unless offset is greater than maxoff. .It Li maxwidth The width of the displayed line. .It Li lines The number of lines. It is used by "more" feature. .It Li tabstops Tab stop width. .It Li work Ns Ar xx Work variable. .Ar xx can be 0 to 31. .El .Sh EXPRESSIONS Almost all expression operators in C are supported except .Sq Li \&~ , .Sq Li \&^ , and unary .Sq Li \&& . Special rules in .Nm are: .Bl -tag -width Identifiers .It Em Identifiers The name of a symbol is translated to the value of the symbol, which is the address of the corresponding object. .Sq Li \&. and .Sq Li \&: can be used in the identifier. If supported by an object format dependent routine, .Sm off .Oo Em filename : Oc Em func : lineno , .Sm on .Oo Em filename : Oc Ns Em variable , and .Oo Em filename : Oc Ns Em lineno can be accepted as a symbol. .It Em Numbers Radix is determined by the first two letters: .Li 0x : hex, .Li 0o : octal, .Li 0t : decimal; otherwise, follow current radix. .It Li \&. `dot' .It Li \&+ `next' .It Li \&.. address of the start of the last line examined. Unlike `dot' or `next', this is only changed by .Dq Li examine or .Dq Li write command. .It Li \&' last address explicitly specified. .It Li \&$ Ns Em variable Translated to the value of the specified variable. It may be followed by a .Li \&: and modifiers as described above. .It Em a Ns Li \&# Ns Em b a binary operator which rounds up the left hand side to the next multiple of right hand side. .It Li \&* Ns Em expr indirection. It may be followed by a .Sq Li \&: and modifiers as described above. .El .Sh SEE ALSO .Xr gdb 1 , .Xr ktr 4 .Sh HISTORY The .Nm debugger was developed for Mach, and ported to .Bx 386 0.1 . This manual page translated from .Fl man macros by Garrett Wollman.