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.\" $DragonFly: src/share/man/man4/ddb.4,v 1.3 2006/05/11 08:23:19 swildner Exp $ 62.Dd May 11, 2006 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. 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 with possible alternate formats depending on the 202machine: 203.Bl -tag -width MIPS -compact 204.It Tn VAX 205don't assume that each external label is a procedure entry mask 206.It Tn i386 207don't round to the next long word boundary 208.It Tn MIPS 209print register contents 210.El 211.El 212.It Cm xf 213Examine forward: 214Execute an examine command with the last specified parameters to it 215except that the next address displayed by it is used as the start address. 216.It Cm xb 217Examine backward: 218Execute an examine command with the last specified parameters to it 219except that the last start address subtracted by the size displayed by it 220is used as the start address. 221.It Cm print Ns Op Cm /acdoruxz 222Print 223.Ar addr Ns s 224according to the modifier character (as described above for 225.Li examine ) . 226Valid formats are: 227.Li a , 228.Li x , 229.Li z , 230.Li o , 231.Li d , 232.Li u , 233.Li r , 234and 235.Li c . 236If no modifier is specified, the last one specified to it is used. 237.Ar addr 238can be a string, in which case it is printed as it is. For example: 239.Bd -literal -offset indent 240print/x \&"eax = \&" $eax \&"\enecx = \&" $ecx \&"\en\&" 241.Ed 242.Pp 243will print like: 244.Bd -literal -offset indent 245eax = xxxxxx 246ecx = yyyyyy 247.Ed 248.It Xo 249.Cm write Ns Op Cm /bhl 250.Ar addr Ar expr1 Op Ar "expr2 ..." 251.Xc 252Write the expressions specified after 253.Ar addr 254on the command line at succeeding locations starting with 255.Ar addr 256The write unit size can be specified in the modifier with a letter 257.Li b 258(byte), 259.Li h 260(half word) or 261.Li l 262(long word) respectively. If omitted, 263long word is assumed. 264.Pp 265.Sy Warning : 266since there is no delimiter between expressions, strange 267things may happen. 268It's best to enclose each expression in parentheses. 269.It Xo 270.Cm set 271.Li \&$ Ns Ar variable 272.Op Li = 273.Ar expr 274.Xc 275Set the named variable or register with the value of 276.Ar expr . 277Valid variable names are described below. 278.It Cm break Ns Op Cm /u 279Set a break point at 280.Ar addr . 281If 282.Ar count 283is supplied, continues 284.Ar count 285- 1 times before stopping at the 286break point. If the break point is set, a break point number is 287printed with 288.Sq Li \&# . 289This number can be used in deleting the break point 290or adding conditions to it. 291.Pp 292If the 293.Li u 294modifier is specified, this command sets a break point in user space 295address. Without the 296.Li u 297option, the address is considered in the kernel 298space, and wrong space address is rejected with an error message. 299This modifier can be used only if it is supported by machine dependent 300routines. 301.Pp 302.Sy Warning : 303If a user text is shadowed by a normal user space debugger, 304user space break points may not work correctly. Setting a break 305point at the low-level code paths may also cause strange behavior. 306.It Cm delete Ar addr 307.It Cm delete Li \&# Ns Ar number 308Delete the break point. The target break point can be specified by a 309break point number with 310.Li # , 311or by using the same 312.Ar addr 313specified in the original 314.Cm break 315command. 316.It Cm step Ns Op Cm /p 317Single step 318.Ar count 319times (the comma is a mandatory part of the syntax). 320If the 321.Li p 322modifier is specified, print each instruction at each step. 323Otherwise, only print the last instruction. 324.Pp 325.Sy Warning : 326depending on machine type, it may not be possible to 327single-step through some low-level code paths or user space code. 328On machines with software-emulated single-stepping (e.g., pmax), 329stepping through code executed by interrupt handlers will probably 330do the wrong thing. 331.It Cm continue Ns Op Cm /c 332Continue execution until a breakpoint or watchpoint. 333If the 334.Li c 335modifier is specified, count instructions while executing. 336Some machines (e.g., pmax) also count loads and stores. 337.Pp 338.Sy Warning : 339when counting, the debugger is really silently single-stepping. 340This means that single-stepping on low-level code may cause strange 341behavior. 342.It Cm until Ns Op Cm /p 343Stop at the next call or return instruction. 344If the 345.Li p 346modifier is specified, print the call nesting depth and the 347cumulative instruction count at each call or return. Otherwise, 348only print when the matching return is hit. 349.It Cm next Ns Op Cm /p 350.It Cm match Ns Op Cm /p 351Stop at the matching return instruction. 352If the 353.Li p 354modifier is specified, print the call nesting depth and the 355cumulative instruction count at each call or return. Otherwise, 356only print when the matching return is hit. 357.It Xo 358.Cm trace Ns Op Cm /u 359.Op Ar frame 360.Op , Ns Ar count 361.Xc 362Stack trace. The 363.Li u 364option traces user space; if omitted, 365.Cm trace 366only traces 367kernel space. 368.Ar count 369is the number of frames to be traced. 370If 371.Ar count 372is omitted, all frames are printed. 373.Pp 374.Sy Warning : 375User space stack trace is valid 376only if the machine dependent code supports it. 377.It Xo 378.Cm search Ns Op Cm /bhl 379.Ar addr 380.Ar value 381.Op Ar mask 382.Op , Ns Ar count 383.Xc 384Search memory for 385.Ar value . 386This command might fail in interesting 387ways if it doesn't find the searched-for value. This is because 388ddb doesn't always recover from touching bad memory. The optional 389.Ar count 390argument limits the search. 391.It Cm show all procs Ns Op Cm /m 392.It Cm ps Ns Op Cm /m 393Display all process information. 394The process information may not be shown if it is not 395supported in the machine, or the bottom of the stack of the 396target process is not in the main memory at that time. 397The 398.Li m 399modifier will alter the display to show VM map 400addresses for the process and not show other info. 401.It Cm show registers Ns Op Cm /u 402Display the register set. 403If the 404.Li u 405option is specified, it displays user registers instead of 406kernel or currently saved one. 407.Pp 408.Sy Warning : 409The support of the 410.Li u 411modifier depends on the machine. If 412not supported, incorrect information will be displayed. 413.It Xo 414.Cm show map Ns Op Cm /f 415.Ar addr 416.Xc 417Prints the VM map at 418.Ar addr . 419If the 420.Li f 421modifier is specified the 422complete map is printed. 423.It Xo 424.Cm show object Ns Op Cm /f 425.Ar addr 426.Xc 427Prints the VM object at 428.Ar addr . 429If the 430.Li f 431option is specified the 432complete object is printed. 433.It Cm "show watches" 434Displays all watchpoints. 435.It Xo 436.Cm watch 437.Ar addr Ns Li \&, Ns Ar size 438.Xc 439Set a watchpoint for a region. Execution stops 440when an attempt to modify the region occurs. 441The 442.Ar size 443argument defaults to 4. 444If you specify a wrong space address, the request is rejected 445with an error message. 446.Pp 447.Sy Warning : 448Attempts to watch wired kernel memory 449may cause unrecoverable error in some systems such as i386. 450Watchpoints on user addresses work best. 451.It Cm gdb 452Toggles between remote GDB and DDB mode. In remote GDB mode, another 453machine is required that runs 454.Xr gdb 1 455using the remote debug feature, with a connection to the serial 456console port on the target machine. Currently only available on the 457.Em i386 458architecture. 459.It Cm help 460Print a short summary of the available commands and command 461abbreviations. 462.El 463.Sh VARIABLES 464The debugger accesses registers and variables as 465.Li \&$ Ns Em name . 466Register names are as in the 467.Dq Cm show registers 468command. 469Some variables are suffixed with numbers, and may have some modifier 470following a colon immediately after the variable name. 471For example, register variables can have a 472.Li u 473modifier to indicate user register (e.g., 474.Li $eax:u ) . 475.Pp 476Built-in variables currently supported are: 477.Bl -tag -width tabstops -compact 478.It Li radix 479Input and output radix 480.It Li maxoff 481Addresses are printed as 'symbol'+offset unless offset is greater than maxoff. 482.It Li maxwidth 483The width of the displayed line. 484.It Li lines 485The number of lines. It is used by "more" feature. 486.It Li tabstops 487Tab stop width. 488.It Li work Ns Ar xx 489Work variable. 490.Ar xx 491can be 0 to 31. 492.El 493.Sh EXPRESSIONS 494Almost all expression operators in C are supported except 495.Sq Li \&~ , 496.Sq Li \&^ , 497and unary 498.Sq Li \&& . 499Special rules in 500.Nm 501are: 502.Bl -tag -width Identifiers 503.It Em Identifiers 504The name of a symbol is translated to the value of the symbol, which 505is the address of the corresponding object. 506.Sq Li \&. 507and 508.Sq Li \&: 509can be used in the identifier. 510If supported by an object format dependent routine, 511.Sm off 512.Oo Em filename : Oc Em func : lineno , 513.Sm on 514.Oo Em filename : Oc Ns Em variable , 515and 516.Oo Em filename : Oc Ns Em lineno 517can be accepted as a symbol. 518.It Em Numbers 519Radix is determined by the first two letters: 520.Li 0x : 521hex, 522.Li 0o : 523octal, 524.Li 0t : 525decimal; otherwise, follow current radix. 526.It Li \&. 527`dot' 528.It Li \&+ 529`next' 530.It Li \&.. 531address of the start of the last line examined. 532Unlike `dot' or `next', this is only changed by 533.Dq Li examine 534or 535.Dq Li write 536command. 537.It Li \&' 538last address explicitly specified. 539.It Li \&$ Ns Em variable 540Translated to the value of the specified variable. 541It may be followed by a 542.Li : 543and modifiers as described above. 544.It Em a Ns Li \&# Ns Em b 545a binary operator which rounds up the left hand side to the next 546multiple of right hand side. 547.It Li \&* Ns Em expr 548indirection. It may be followed by a 549.Sq Li : 550and modifiers as described above. 551.El 552.Sh SEE ALSO 553.Xr gdb 1 554.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