1.\" 2.\" Mach Operating System 3.\" Copyright (c) 1991,1990 Carnegie Mellon University 4.\" All Rights Reserved. 5.\" 6.\" Permission to use, copy, modify and distribute this software and its 7.\" documentation is hereby granted, provided that both the copyright 8.\" notice and this permission notice appear in all copies of the 9.\" software, derivative works or modified versions, and any portions 10.\" thereof, and that both notices appear in supporting documentation. 11.\" 12.\" CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" 13.\" CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR 14.\" ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. 15.\" 16.\" Carnegie Mellon requests users of this software to return to 17.\" 18.\" Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU 19.\" School of Computer Science 20.\" Carnegie Mellon University 21.\" Pittsburgh PA 15213-3890 22.\" 23.\" any improvements or extensions that they make and grant Carnegie Mellon 24.\" the rights to redistribute these changes. 25.\" 26.\" changed a \# to #, since groff choked on it. 27.\" 28.\" HISTORY 29.\" ddb.4,v 30.\" Revision 1.1 1993/07/15 18:41:02 brezak 31.\" Man page for DDB 32.\" 33.\" Revision 2.6 92/04/08 08:52:57 rpd 34.\" Changes from OSF. 35.\" [92/01/17 14:19:22 jsb] 36.\" Changes for OSF debugger modifications. 37.\" [91/12/12 tak] 38.\" 39.\" Revision 2.5 91/06/25 13:50:22 rpd 40.\" Added some watchpoint explanation. 41.\" [91/06/25 rpd] 42.\" 43.\" Revision 2.4 91/06/17 15:47:31 jsb 44.\" Added documentation for continue/c, match, search, and watchpoints. 45.\" I've not actually explained what a watchpoint is; maybe Rich can 46.\" do that (hint, hint). 47.\" [91/06/17 10:58:08 jsb] 48.\" 49.\" Revision 2.3 91/05/14 17:04:23 mrt 50.\" Correcting copyright 51.\" 52.\" Revision 2.2 91/02/14 14:10:06 mrt 53.\" Changed to new Mach copyright 54.\" [91/02/12 18:10:12 mrt] 55.\" 56.\" Revision 2.2 90/08/30 14:23:15 dbg 57.\" Created. 58.\" [90/08/30 dbg] 59.\" 60.\" $FreeBSD: src/share/man/man4/ddb.4,v 1.7.2.6 2001/08/17 13:08:37 ru Exp $ 61.\" 62.Dd May 7, 2011 63.Dt DDB 4 64.Os 65.Sh NAME 66.Nm ddb 67.Nd interactive kernel debugger 68.Sh SYNOPSIS 69.Cd options DDB 70.Pp 71.Cd options DDB_TRACE 72.Cd options DDB_UNATTENDED 73.Sh DESCRIPTION 74The 75.Nm 76kernel debugger has most of the features of the old kdb, 77but with a more rational syntax 78inspired by 79.Xr gdb 1 . 80If linked into the running kernel, 81it can be invoked locally with the 82.Ql debug 83.Xr keymap 5 84action (the default is Control-Alt-Esc). 85The debugger is also invoked on kernel 86.Xr panic 9 87if the 88.Va debug.debugger_on_panic 89.Xr sysctl 8 90MIB variable is set non-zero, 91which is the default 92unless the 93.Dv DDB_UNATTENDED 94option is specified. 95If set, the 96.Va debug.trace_on_panic 97.Xr sysctl 8 98MIB variable will cause 99.Nm 100to print a stack trace on 101.Xr panic 9 . 102It is zero by default unless the 103.Dv DDB_TRACE 104option is specified. 105.Pp 106The current location is called `dot'. The `dot' is displayed with 107a hexadecimal format at a prompt. 108Examine and write commands update `dot' to the address of the last line 109examined or the last location modified, and set `next' to the address of 110the next location to be examined or changed. 111Other commands don't change `dot', and set `next' to be the same as `dot'. 112.Pp 113The general command syntax is: 114.Cm command Ns Op Li \&/ Ns Ar modifier 115.Ar address Ns Op Li , Ns Ar count 116.Pp 117A blank line repeats the previous command from the address `next' with 118count 1 and no modifiers. Specifying 119.Ar address 120sets `dot' to the 121address. Omitting 122.Ar address 123uses `dot'. A missing 124.Ar count 125is taken 126to be 1 for printing commands or infinity for stack traces. 127.Pp 128The 129.Nm 130debugger has a feature like the 131.Xr more 1 132command 133for the output. If an output line exceeds the number set in the 134.Li \&$lines 135variable, it displays 136.Dq Em --db_more-- 137and waits for a response. 138The valid responses for it are: 139.Pp 140.Bl -tag -compact -width SPC 141.It Li SPC 142one more page 143.It Li RET 144one more line 145.It Li q 146abort the current command, and return to the command input mode 147.El 148.Pp 149Finally, 150.Nm 151provides a small (currently 10 items) command history, and offers 152simple emacs-style command line editing capabilities. In addition to 153the emacs control keys, the usual ANSI arrow keys might be used to 154browse through the history buffer, and move the cursor within the 155current line. 156.Sh COMMANDS 157.Bl -ohang 158.It Cm examine 159.It Cm x 160Display the addressed locations according to the formats in the modifier. 161Multiple modifier formats display multiple locations. 162If no format is specified, the last formats specified for this command 163is used. 164.Pp 165The format characters are: 166.Bl -tag -compact -width indent 167.It Li b 168look at by bytes (8 bits) 169.It Li h 170look at by half words (16 bits) 171.It Li l 172look at by long words (32 bits) 173.It Li a 174print the location being displayed 175.It Li A 176print the location with a line number if possible 177.It Li x 178display in unsigned hex 179.It Li z 180display in signed hex 181.It Li o 182display in unsigned octal 183.It Li d 184display in signed decimal 185.It Li u 186display in unsigned decimal 187.It Li r 188display in current radix, signed 189.It Li c 190display low 8 bits as a character. 191Non-printing characters are displayed as an octal escape code (e.g., `\e000'). 192.It Li s 193display the null-terminated string at the location. 194Non-printing characters are displayed as octal escapes. 195.It Li m 196display in unsigned hex with character dump at the end of each line. 197The location is also displayed in hex at the beginning of each line. 198.It Li i 199display as an instruction 200.It Li I 201display as an instruction; on i386, don't round to the next long word boundary. 202.El 203.It Cm xf 204Examine forward: 205Execute an examine command with the last specified parameters to it 206except that the next address displayed by it is used as the start address. 207.It Cm xb 208Examine backward: 209Execute an examine command with the last specified parameters to it 210except that the last start address subtracted by the size displayed by it 211is used as the start address. 212.It Cm print Ns Op Cm /acdoruxz 213Print 214.Ar addr Ns s 215according to the modifier character (as described above for 216.Li examine ) . 217Valid formats are: 218.Li a , 219.Li x , 220.Li z , 221.Li o , 222.Li d , 223.Li u , 224.Li r , 225and 226.Li c . 227If no modifier is specified, the last one specified to it is used. 228.Ar addr 229can be a string, in which case it is printed as it is. For example: 230.Bd -literal -offset indent 231print/x \&"eax = \&" $eax \&"\enecx = \&" $ecx \&"\en\&" 232.Ed 233.Pp 234will print like: 235.Bd -literal -offset indent 236eax = xxxxxx 237ecx = yyyyyy 238.Ed 239.It Xo 240.Cm write Ns Op Cm /bhl 241.Ar addr Ar expr1 Op Ar "expr2 ..." 242.Xc 243Write the expressions specified after 244.Ar addr 245on the command line at succeeding locations starting with 246.Ar addr 247The write unit size can be specified in the modifier with a letter 248.Li b 249(byte), 250.Li h 251(half word) or 252.Li l 253(long word) respectively. If omitted, 254long word is assumed. 255.Pp 256.Sy Warning : 257since there is no delimiter between expressions, strange 258things may happen. 259It's best to enclose each expression in parentheses. 260.It Xo 261.Cm set 262.Li \&$ Ns Ar variable 263.Op Li = 264.Ar expr 265.Xc 266Set the named variable or register with the value of 267.Ar expr . 268Valid variable names are described below. 269.It Cm break Ns Op Cm /u 270Set a break point at 271.Ar addr . 272If 273.Ar count 274is supplied, continues 275.Ar count 276- 1 times before stopping at the 277break point. If the break point is set, a break point number is 278printed with 279.Sq Li \&# . 280This number can be used in deleting the break point 281or adding conditions to it. 282.Pp 283If the 284.Li u 285modifier is specified, this command sets a break point in user space 286address. Without the 287.Li u 288option, the address is considered in the kernel 289space, and wrong space address is rejected with an error message. 290This modifier can be used only if it is supported by machine dependent 291routines. 292.Pp 293.Sy Warning : 294If a user text is shadowed by a normal user space debugger, 295user space break points may not work correctly. Setting a break 296point at the low-level code paths may also cause strange behavior. 297.It Cm delete Ar addr 298.It Cm delete Li \&# Ns Ar number 299Delete the break point. The target break point can be specified by a 300break point number with 301.Li # , 302or by using the same 303.Ar addr 304specified in the original 305.Cm break 306command. 307.It Cm step Ns Op Cm /p 308Single step 309.Ar count 310times (the comma is a mandatory part of the syntax). 311If the 312.Li p 313modifier is specified, print each instruction at each step. 314Otherwise, only print the last instruction. 315.Pp 316.Sy Warning : 317depending on machine type, it may not be possible to 318single-step through some low-level code paths or user space code. 319On machines with software-emulated single-stepping (e.g., pmax), 320stepping through code executed by interrupt handlers will probably 321do the wrong thing. 322.It Cm continue Ns Op Cm /c 323Continue execution until a breakpoint or watchpoint. 324If the 325.Li c 326modifier is specified, count instructions while executing. 327Some machines (e.g., pmax) also count loads and stores. 328.Pp 329.Sy Warning : 330when counting, the debugger is really silently single-stepping. 331This means that single-stepping on low-level code may cause strange 332behavior. 333.It Cm until Ns Op Cm /p 334Stop at the next call or return instruction. 335If the 336.Li p 337modifier is specified, print the call nesting depth and the 338cumulative instruction count at each call or return. Otherwise, 339only print when the matching return is hit. 340.It Cm next Ns Op Cm /p 341.It Cm match Ns Op Cm /p 342Stop at the matching return instruction. 343If the 344.Li p 345modifier is specified, print the call nesting depth and the 346cumulative instruction count at each call or return. Otherwise, 347only print when the matching return is hit. 348.It Xo 349.Cm trace Ns Op Cm /u 350.Op Ar frame 351.Op , Ns Ar count 352.Xc 353Stack trace. The 354.Li u 355option traces user space; if omitted, 356.Cm trace 357only traces 358kernel space. 359.Ar count 360is the number of frames to be traced. 361If 362.Ar count 363is omitted, all frames are printed. 364.Pp 365.Sy Warning : 366User space stack trace is valid 367only if the machine dependent code supports it. 368.It Xo 369.Cm search Ns Op Cm /bhl 370.Ar addr 371.Ar value 372.Op Ar mask 373.Op , Ns Ar count 374.Xc 375Search memory for 376.Ar value . 377This command might fail in interesting 378ways if it doesn't find the searched-for value. This is because 379ddb doesn't always recover from touching bad memory. The optional 380.Ar count 381argument limits the search. 382.It Cm show all procs Ns Op Cm /m 383.It Cm ps Ns Op Cm /m 384Display all process information. 385The process information may not be shown if it is not 386supported in the machine, or the bottom of the stack of the 387target process is not in the main memory at that time. 388The 389.Li m 390modifier will alter the display to show VM map 391addresses for the process and not show other info. 392.It Cm show registers Ns Op Cm /u 393Display the register set. 394If the 395.Li u 396option is specified, it displays user registers instead of 397kernel or currently saved one. 398.Pp 399.Sy Warning : 400The support of the 401.Li u 402modifier depends on the machine. If 403not supported, incorrect information will be displayed. 404.It Xo 405.Cm show map Ns Op Cm /f 406.Ar addr 407.Xc 408Prints the VM map at 409.Ar addr . 410If the 411.Li f 412modifier is specified the 413complete map is printed. 414.It Xo 415.Cm show object Ns Op Cm /f 416.Ar addr 417.Xc 418Prints the VM object at 419.Ar addr . 420If the 421.Li f 422option is specified the 423complete object is printed. 424.It Cm show ktr Ns Op Cm /v 425Prints the contents of 426.Xr ktr 4 427buffer. 428If the 429.Li v 430modifier is specified, timestamp, filename and line number are displayed 431with each log entry. 432.It Cm "show watches" 433Displays all watchpoints. 434.It Xo 435.Cm watch 436.Ar addr Ns Li \&, Ns Ar size 437.Xc 438Set a watchpoint for a region. Execution stops 439when an attempt to modify the region occurs. 440The 441.Ar size 442argument defaults to 4. 443If you specify a wrong space address, the request is rejected 444with an error message. 445.Pp 446.Sy Warning : 447Attempts to watch wired kernel memory 448may cause unrecoverable error in some systems such as i386. 449Watchpoints on user addresses work best. 450.It Cm gdb 451Toggles between remote GDB and DDB mode. In remote GDB mode, another 452machine is required that runs 453.Xr gdb 1 454using the remote debug feature, with a connection to the serial 455console port on the target machine. Currently only available on the 456.Em i386 457architecture. 458.It Cm help 459Print a short summary of the available commands and command 460abbreviations. 461.El 462.Sh VARIABLES 463The debugger accesses registers and variables as 464.Li \&$ Ns Em name . 465Register names are as in the 466.Dq Cm show registers 467command. 468Some variables are suffixed with numbers, and may have some modifier 469following a colon immediately after the variable name. 470For example, register variables can have a 471.Li u 472modifier to indicate user register (e.g., 473.Li $eax:u ) . 474.Pp 475Built-in variables currently supported are: 476.Bl -tag -width tabstops -compact 477.It Li radix 478Input and output radix 479.It Li maxoff 480Addresses are printed as 'symbol'+offset unless offset is greater than maxoff. 481.It Li maxwidth 482The width of the displayed line. 483.It Li lines 484The number of lines. It is used by "more" feature. 485.It Li tabstops 486Tab stop width. 487.It Li work Ns Ar xx 488Work variable. 489.Ar xx 490can be 0 to 31. 491.El 492.Sh EXPRESSIONS 493Almost all expression operators in C are supported except 494.Sq Li \&~ , 495.Sq Li \&^ , 496and unary 497.Sq Li \&& . 498Special rules in 499.Nm 500are: 501.Bl -tag -width Identifiers 502.It Em Identifiers 503The name of a symbol is translated to the value of the symbol, which 504is the address of the corresponding object. 505.Sq Li \&. 506and 507.Sq Li \&: 508can be used in the identifier. 509If supported by an object format dependent routine, 510.Sm off 511.Oo Em filename : Oc Em func : lineno , 512.Sm on 513.Oo Em filename : Oc Ns Em variable , 514and 515.Oo Em filename : Oc Ns Em lineno 516can be accepted as a symbol. 517.It Em Numbers 518Radix is determined by the first two letters: 519.Li 0x : 520hex, 521.Li 0o : 522octal, 523.Li 0t : 524decimal; otherwise, follow current radix. 525.It Li \&. 526`dot' 527.It Li \&+ 528`next' 529.It Li \&.. 530address of the start of the last line examined. 531Unlike `dot' or `next', this is only changed by 532.Dq Li examine 533or 534.Dq Li write 535command. 536.It Li \&' 537last address explicitly specified. 538.It Li \&$ Ns Em variable 539Translated to the value of the specified variable. 540It may be followed by a 541.Li : 542and modifiers as described above. 543.It Em a Ns Li \&# Ns Em b 544a binary operator which rounds up the left hand side to the next 545multiple of right hand side. 546.It Li \&* Ns Em expr 547indirection. It may be followed by a 548.Sq Li : 549and modifiers as described above. 550.El 551.Sh SEE ALSO 552.Xr gdb 1 , 553.Xr ktr 4 554.Sh HISTORY 555The 556.Nm 557debugger was developed for Mach, and ported to 558.Bx 386 0.1 . 559This manual page translated from 560.Fl man 561macros by Garrett Wollman. 562