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SunOS man pages : mdb (1)

User Commands                                              mdb(1)

NAME

mdb - modular debugger

SYNOPSIS

mdb [ -kmuwyAFMS ] [ _o option ] [ -p pid ] [ -s distance ] [ -I path ] [ -L path ] [ -P prompt ] [ -R root ] [ -V dis-version ] [ object [ core ] | core | suffix ]

DESCRIPTION

Introduction The mdb utility is an extensible utility for low-level debugging and editing of the live operating system, operat- ing system crash dumps, user processes, user process core dumps, and object files. For a more detailed description of mdb features, refer to the manual, Solaris Modular Debugger Guide. Debugging is the process of analyzing the execution and state of a software program in order to remove defects. Traditional debugging tools provide facilities for execution control so that programmers can re-execute programs in a controlled environment and display the current state of pro- gram data or evaluate expressions in the source language used to develop the program. Unfortunately, these techniques are often inappropriate for debugging complex software systems such as an operating sys- tem, where bugs may not be reproducible and program state is massive and distributed, for programs that are highly optim- ized, have had their debug information removed, or are them- selves low-level debugging tools, or for customer situations where the developer can only access post-mortem information. mdb provides a completely customizable environment for debugging these programs and scenarios, including a dynamic module facility that programmers can use to implement their own debugging commands to perform program-specific analysis. Each mdb module can be used to examine the program in several different contexts, including live and post-mortem. Definitions The target is the program being inspected by the debugger. mdb currently provides support for the following types of targets: user processes, user process core files, the live operating system (via /dev/kmem and /dev/ksyms), operating system crash dumps, user process images recorded inside an operating system crash dump, and ELF object files. Each tar- get exports a standard set of properties, including one or more address spaces, one or more symbol tables, a set of load objects, and a set of threads that can be examined using the debugger commands described below. SunOS 5.8 Last change: 14 Sep 1999 1 User Commands mdb(1) A debugger command, or dcmd (pronounced dee-command) in mdb terminology, is a routine in the debugger that can access any of the properties of the current target. mdb parses com- mands from standard input, and then executes the correspond- ing dcmds. Each dcmd can also accept a list of string or numerical arguments, as shown in the syntax description below. mdb contains a set of built-in dcmds, described below, that are always available. You can also extend the capabilities of mdb itself by writing your own dcmds, as described in the Solaris Modular Debugger Guide. A walker is a set of routines that describe how to walk, or iterate, through the elements of a particular program data structure. A walker encapsulates the data structure's imple- mentation from dcmds and from mdb itself. You can use walk- ers interactively, or use them as a primitive to build other dcmds or walkers. As with dcmds, you can extend mdb by implementing your own walkers as part of a debugger module. A debugger module, or dmod (pronounced dee-mod), is a dynam- ically loaded library containing a set of dcmds and walkers. During initialization, mdb will attempt to load dmods corresponding to the load objects present in the tar- get. You can subsequently load or unload dmods at any time while running mdb. mdb ships with a set of standard dmods for debugging the Solaris kernel. The Solaris Modular Debugger Guide contains more information on developing your own debugger modules. A macro file is a text file containing a set of commands to execute. Macro files are typically used to automate the pro- cess of displaying a simple data structure. mdb provides complete backward compatibility for the execution of macro files written for adb(1), and the Solaris installation includes a set of macro files for debugging the Solaris ker- nel that may be used with either tool. Syntax The debugger processes commands from standard input. If standard input is a terminal, mdb provides terminal editing capabilities. mdb can also process commands from macro files and from dcmd pipelines, described below. The language syn- tax is designed around the concept of computing the value of an expression (typically a memory address in the target), and then applying a dcmd to that address. The current address location is referred to as dot, and its value is referenced using ``.''. A metacharacter is one of the following characters: SunOS 5.8 Last change: 14 Sep 1999 2 User Commands mdb(1) [ ] | ! / \ ? = > $ : ; NEWLINE SPACE TAB A blank is a TAB or a SPACE. A word is a sequence of charac- ters separated by one or more non-quoted metacharacters. Some of the metacharacters only function as delimiters in certain contexts, as described below. An identifier is a sequence of letters, digits, underscores, periods, or backquotes beginning with a letter, underscore, or period. Identifiers are used as the names of symbols, variables, dcmds, and walkers. Commands are delimited by a NEWLINE or semicolon ( ; ). A dcmd is denoted by one of the following words or metachar- acters: / \ ? = > $character :character ::identifier dcmds named by metacharacters or prefixed by a single $ or : are provided as builtin operators, and implement complete compatibility with the command set of the legacy adb(1) utility. Once a dcmd has been parsed, the /, \, ?, =, >, $, and : characters are no longer recognized as metacharacters until the termination of the argument list. A simple-command is a dcmd followed by a sequence or zero or more blank-separated words. The words are passed as argu- ments to the invoked dcmd, except as specified under Quoting and Arithmetic Expansion below. Each dcmd returns an exit status that indicates it was either successful, failed, or was invoked with invalid arguments. A pipeline is a sequence of one or more simple commands separated by |. Unlike the shell, dcmds in mdb pipelines are not executed as separate processes. After the pipeline has been parsed, each dcmd is invoked in order from left to right. Each dcmd's output is processed and stored as described under dcmd Pipelines below. Once the left-hand dcmd is complete, its processed output is used as input for the next dcmd in the pipeline. If any dcmd does not return a successful exit status, the pipeline is aborted. An expression is a sequence of words that is evaluated to compute a 64-bit unsigned integer value. The words are evaluated using the rules described under Arithmetic Expan- sion below. Commands A command is one of the following: SunOS 5.8 Last change: 14 Sep 1999 3 User Commands mdb(1) pipeline [! word ...] [ ; ] A simple-command or pipeline can be optionally suf- fixed with the ! character, indicating that the debugger should open a pipe(2) and send the standard output of the last dcmd in the mdb pipeline to an external process created by executing $SHELL -c fol- lowed by the string formed by concatenating the words after the ! character. For more details, refer to Shell Escapes below. expression pipeline [! word ...] [ ; ] A simple-command or pipeline can be prefixed with an expression. Before execution of the pipeline, the value of dot (the variable denoted by ``.'') is set to the value of the expression. expression , expression pipeline [! word ...] [ ; ] A simple-command or pipeline can be prefixed with two expressions. The first is evaluated to determine the new value of dot, and the second is evaluated to determine a repeat count for the first dcmd in the pipeline. This dcmd will be executed count times before the next dcmd in the pipeline is executed. The repeat count only applies to the first dcmd in the pipeline. , expression pipeline [! word ...] [ ; ] If the initial expression is omitted, dot is not modi- fied but the first dcmd in the pipeline will be repeated according to the value of the expression. expression [! word ...] [ ; ] A command can consist only of an arithmetic expres- sion. The expression is evaluated and the dot variable is set to its value, and then the previous dcmd and arguments are executed using the new value of dot. expression, expression [! word ...] [ ; ] A command can consist only of a dot expression and repeat count expression. After dot is set to the value of the first expression, the previous dcmd and argu- ments are repeatedly executed the number of times specified by the value of the second expression. , expression [! word ...] [ ; ] If the initial expression is omitted, dot is not modi- fied but the previous dcmd and arguments are repeat- edly executed the number of times specified by the value of the count expression. ! word ... [ ; ] If the command begins with the ! character, no dcmds SunOS 5.8 Last change: 14 Sep 1999 4 User Commands mdb(1) are executed and the debugger simply executes $SHELL -c followed by the string formed by concatenating the words after the ! character. Comments A word beginning with // causes that word and all the subse- quent characters up to a NEWLINE to be ignored. Arithmetic Expansion Arithmetic expansion is performed when an mdb command is preceded by an optional expression representing a start address, or a start address and a repeat count. Arithmetic expansion can also be performed to compute a numerical argu- ment for a dcmd. An arithmetic expression can appear in an argument list enclosed in square brackets preceded by a dol- lar sign ($[ expression ]), and will be replaced by the value of the expression. Expressions may contain any of the following special words: integer The specified integer value. Integer values may be prefixed with 0i or 0I to indicate binary values, 0o or 0O to indicate octal values, 0t or 0T to indicate decimal values, and 0x or 0X to indicate hexadecimal values (the default). 0[tT][0-9]+.[0-9]+ The specified decimal floating point value, converted to its IEEE double-precision floating point represen- tation. 'cccccccc' The integer value computed by converting each charac- ter to a byte equal to its ASCII value. Up to eight characters may be specified in a character constant. Characters are packed into the integer in reverse order (right-to-left) beginning at the least signifi- cant byte. <identifier The value of the variable named by identifier. identifier The value of the symbol named by identifier. (expression) The value of expression. . The value of dot. & The most recent value of dot used to execute a dcmd. SunOS 5.8 Last change: 14 Sep 1999 5 User Commands mdb(1) + The value of dot incremented by the current increment. ^ The value of dot decremented by the current increment. The increment is a global variable that stores the total bytes read by the last formatting dcmd. For more information on the increment, refer to the discussion of Formatting dcmds below. Unary operators are right associative and have higher pre- cedence than binary operators. The unary operators are: #expression Logical negation. ~expression Bitwise complement. -expression Integer negation. %expression The value of a pointer-sized quantity at the object file location corresponding to virtual address expres- sion in the target's virtual address space. %/[csil]/expression The value of a char, short, int, or long-sized quan- tity at the object file location corresponding to vir- tual address expression in the target's virtual address space. %/[1248]/expression The value of a one, two, four, or eight-byte quantity at the object file location corresponding to virtual address expression in the target's virtual address space. *expression The value of a pointer-sized quantity at virtual address expression in the target's virtual address space. */[csil]/expression The value of a char, short, int, or long-sized quan- tity at virtual address expression in the target's virtual address space. */[1248]/expression The value of a one, two, four, or eight-byte quantity at virtual address expression in the target's virtual address space. SunOS 5.8 Last change: 14 Sep 1999 6 User Commands mdb(1) Binary operators are left associative and have lower pre- cedence than unary operators. The binary operators, in order of precedence from highest to lowest, are: * Integer multiplication. % Integer division. # Left-hand side rounded up to next multiple of right- hand side. + Integer addition. - Integer subtraction. << Bitwise shift left. >> Bitwise shift right. == Logical equality. != Logical inequality. & Bitwise AND. ^ Bitwise exclusive OR. | Bitwise inclusive OR. Quoting Each metacharacter described above (see Syntax) terminates a word unless quoted. Characters can be quoted (forcing mdb to interpret each character as itself without any special sig- nificance) by enclosing them in a pair of single (') or dou- ble (") quote marks. A single quote cannot appear within single quotes. Inside double quotes, mdb recognizes the C programming language character escape sequences. Shell Escapes The ! character can be used to create a pipeline between an mdb command and the user's shell. If the $SHELL environment variable is set, mdb will fork and exec this program for shell escapes; otherwise /bin/sh is used. The shell is invoked with the -c option followed by a string formed by concatenating the words after the ! character. The ! charac- ter takes precedence over all other metacharacters, except semicolon (;) and NEWLINE. Once a shell escape is detected, the remaining characters up to the next semicolon or NEWLINE are passed as is to the shell. The output of shell commands may not be piped to mdb dcmds. Commands executed by a shell escape have their output sent directly to the terminal, not to mdb. SunOS 5.8 Last change: 14 Sep 1999 7 User Commands mdb(1) Variables A variable is a variable name, a corresponding integer value, and a set of attributes. A variable name is a sequence of letters, digits, underscores, or periods. A variable can be assigned a value using the > dcmd or ::typeset dcmd, and its attributes can be manipulated using the ::typeset dcmd. Each variable's value is represented as a 64-bit unsigned integer. A variable may have one or more of the following attributes: read-only (cannot be modified by the user), persistent (cannot be unset by the user), and tagged (user-defined indicator). The following variables are defined as persistent: 0 The most recent value printed using the /, \, ?, or = dcmd. 9 The most recent count used with the $< dcmd. b The virtual address of the base of the data sec- tion. d The size of the data section in bytes. e The virtual address of the entry point. m The initial bytes (magic number) of the target's primary object file, or zero if no object file has been read yet. t The size of the text section in bytes. In addition, the mdb kernel and process targets will export the current values of the representative thread's register set as named variables. The names of these variables will depend on the target's platform and instruction set archi- tecture. Symbol Name Resolution As explained in the Syntax description above, a symbol iden- tifier present in an expression context evaluates to the value of this symbol. The value typically denotes the vir- tual address of the storage associated with the symbol in the target's virtual address space. A target may support multiple symbol tables including, but not limited to, a pri- mary executable symbol table, a primary dynamic symbol table, a run-time link-editor symbol table, and standard and dynamic symbol tables for each of a number of load objects (such as shared libraries in a user process, or kernel modules in the Solaris kernel). The target typically searches the primary executable's symbol tables first, and SunOS 5.8 Last change: 14 Sep 1999 8 User Commands mdb(1) then one or more of the other symbol tables. Notice that ELF symbol tables only contain entries for external, global, and static symbols; automatic symbols do not appear in the sym- bol tables processed by mdb. Additionally, mdb provides a private user-defined symbol table that is searched prior to any of the target symbol tables. The private symbol table is initially empty, and can be manipulated using the ::nmadd and ::nmdel dcmds. The ::nm -P option can be used to display the contents of the private symbol table. The private symbol table allows the user to create symbol definitions for program functions or data that were either missing from the original program or stripped out. These definitions are then used whenever mdb converts a symbolic name to an address, or an address to the nearest symbol. As targets contain multiple symbol tables, and each symbol table may include symbols from multiple object files, dif- ferent symbols with the same name may exist. mdb uses the backquote (`) character as a symbol name scoping operator to allow the programmer to obtain the value of the desired sym- bol in this situation. The programmer can specify the scope used to resolve a symbol name as either: object`name, or file`name, or object`file`name. The object identifier refers to the name of a load object. The file identifier refers to the basename of a source file that has a symbol of type STT_FILE in the specified object's symbol table. The object identifier's interpretation depends on the target type. The mdb kernel target expects object to specify the basename of a loaded kernel module. For example, the symbol name: specfs`_init evaluates to the value of the _init symbol in the specfs kernel module. The mdb process target expects object to specify the name of the executable or of a loaded shared library. It may take any of the following forms: 1. An exact match (that is, a full pathname): /usr/lib/libc.so.1 2. An exact basename match: libc.so.1 3. An initial basename match up to a ``.'' suffix: libc.so or libc 4. The literal string a.out is accepted as an alias for the executable. SunOS 5.8 Last change: 14 Sep 1999 9 User Commands mdb(1) In the case of a naming conflict between symbols and hexade- cimal integer values, mdb will attempt to evaluate an ambi- guous token as a symbol first, before evaluating it as an integer value. For example, the token f may either refer to the decimal integer value 15 specified in hexadecimal (the default base), or to a global variable named f in the target's symbol table. If a symbol with an ambiguous name is present, the integer value can be specified by using an explicit 0x or 0X prefix. dcmd and Walker Name Resolution As described earlier, each mdb dmod provides a set of dcmds and walkers. dcmds and walkers are tracked in two distinct, global namespaces. mdb also keeps track of a dcmd and walker namespace associated with each dmod. Identically named dcmds or walkers within a given dmod are not allowed: a dmod with this type of naming conflict will fail to load. Name con- flicts between dcmds or walkers from different dmods are allowed in the global namespace. In the case of a conflict, the first dcmd or walker with that particular name to be loaded is given precedence in the global namespace. Alter- nate definitions are kept in a list in load order. The backquote character (`) may be used in a dcmd or walker name as a scoping operator to select an alternate definition. For example, if dmods m1 and m2 each provide a dcmd d, and m1 is loaded prior to m2, then: ::d Executes m1's definition of d. ::m1`d Executes m1's definition of d. ::m2`d Executes m2's definition of d. If module m1 were now unloaded, the next dcmd on the global definition list (m2`d) would be promoted to global visibil- ity. The current definition of a dcmd or walker can be determined using the ::which dcmd, described below. The glo- bal definition list can be displayed using the ::which -v option. dcmd Pipelines dcmds can be composed into a pipeline using the | operator. The purpose of a pipeline is to pass a list of values, typi- cally virtual addresses, from one dcmd or walker to another. Pipeline stages might be used to map a pointer from one type of data structure to a pointer to a corresponding data structure, to sort a list of addresses, or to select the addresses of structures with certain properties. SunOS 5.8 Last change: 14 Sep 1999 10 User Commands mdb(1) mdb executes each dcmd in the pipeline in order from left to right. The leftmost dcmd is executed using the current value of dot, or using the value specified by an explicit expres- sion at the start of the command. When a | operator is encountered, mdb creates a pipe (a shared buffer) between the output of the dcmd to its left and the mdb parser, and an empty list of values. As the dcmd executes, its standard output is placed in the pipe and then consumed and evaluated by the parser, as if mdb were reading this data from stan- dard input. Each line must consist of an arithmetic expres- sion terminated by a NEWLINE or semicolon (;). The value of the expression is appended to the list of values associated with the pipe. If a syntax error is detected, the pipeline is aborted. When the dcmd to the left of a | operator completes, the list of values associated with the pipe is then used to invoke the dcmd to the right of the | operator. For each value in the list, dot is set to this value and the right- hand dcmd is executed. Only the rightmost dcmd in the pipe- line has its output printed to standard output. If any dcmd in the pipeline produces output to standard error, these messages are printed directly to standard error and are not processed as part of the pipeline. Signal Handling The debugger ignores the PIPE and QUIT signals. The INT sig- nal aborts the command that is currently executing. The debugger intercepts and provides special handling for the ILL, TRAP, EMT, FPE, BUS, and SEGV signals. If any of these signals are generated asynchronously (that is, delivered from another process using kill(2)), mdb will restore the signal to its default disposition and dump core. However, if any of these signals are generated synchronously by the debugger process itself and a dcmd from an externally loaded dmod is currently executing, and standard input is a termi- nal, mdb will provide a menu of choices allowing the user to force a core dump, quit without producing a core dump, stop for attach by a debugger, or attempt to resume. The resume option will abort all active commands and unload the dmod whose dcmd was active at the time the fault occurred. It can then be subsequently re-loaded by the user. The resume option provides limited protection against buggy dcmds. Refer to WARNINGS, Use of the Error Recovery Mechanism, below for information about the risks associated with the resume option. Command Re-entry The text of the last HISTSIZE (default 128) commands entered from a terminal device are saved in memory. The in- line editing facility, described next, provides key mappings for searching and fetching elements from the history list. SunOS 5.8 Last change: 14 Sep 1999 11 User Commands mdb(1) In-line Editing If standard input is a terminal device, mdb provides some simple emacs-style facilities for editing the command line. The search, previous, and next commands in edit mode provide access to the history list. Only strings, not patterns, are matched when searching. In the table below, the notation for control characters is caret (^) followed by a character shown in upper case. The notation for escape sequences is M- followed by a character. For example, M-f (pronounced meta- eff) is entered by depressing <ESC> followed by 'f', or by depressing Meta followed by 'f' on keyboards that support a Meta key. A command line is committed and executed using RETURN or NEWLINE. The edit commands are: ^F Move cursor forward (right) one character. M-f Move cursor forward one word. ^B Move cursor backward (left) one character. M-b Move cursor backward one word. ^A Move cursor to start of line. ^E Move cursor to end of line. ^D Delete current character, if the current line is not empty. If the current line is empty, ^D denotes EOF and the debugger will exit. ^K Delete from the cursor to the end of the line. ^L Reprint the current line. ^T Transpose current character with next character. ^N Fetch the next command from the history. Each time ^N is entered, the next command forward in time is retrieved. ^P Fetch the previous command from the history. Each time ^P is entered, the next command backward in time is retrieved. ^R[string] Search backward in the history for a previous command line containing string. The string should be ter- minated by a RETURN or NEWLINE. If string is omitted, the previous history element containing the most recent string is retrieved. SunOS 5.8 Last change: 14 Sep 1999 12 User Commands mdb(1) The editing mode also interprets the following user-defined sequences as editing commands. User defined sequences can be read or modified using the stty(1) command. erase User defined erase character (usually ^H or ^?). Delete previous character. intr User defined interrupt character (usually ^C). Abort the current command and print a new prompt. kill User defined kill character (usually ^U). Kill the entire current command line. quit User defined quit character (usually ^\). Quit the debugger. suspend User defined suspend character (usually ^Z). Suspend the debugger. On keyboards that support an extended keypad with arrow keys, mdb will interpret these keystrokes as editing com- mands: up-arrow Fetch the previous command from the history (same as ^P). down-arrow Fetch the next command from the history (same as ^N). left-arrow Move cursor backward one character (same as ^B). right-arrow Move cursor forward one character (same as ^F). Output Pager mdb provides a built-in output pager. The output pager is enabled if the debugger's standard output is a terminal dev- ice. Each time a command is executed, mdb will pause after one screenful of output is produced and will display a pager prompt: >> More [<space>, <cr>, q, n, c, a] ? The following key sequences are recognized by the pager: SPACE Display the next screenful of output. a, A Abort the current top-level command and return to the prompt. SunOS 5.8 Last change: 14 Sep 1999 13 User Commands mdb(1) c, C Continue displaying output without pausing at each screenful until the current top-level command is com- plete. n, N, NEWLINE, RETURN Display the next line of output. q, Q, ^C, ^\ Quit (abort) the current dcmd only. Formatting dcmds The /, \, ?, and = metacharacters are used to denote the special output formatting dcmds. Each of these dcmds accepts an argument list consisting of one or more format charac- ters, repeat counts, or quoted strings. A format character is one of the ASCII characters shown in the table below. Format characters are used to read and format data from the target. A repeat count is a positive integer preceding the format character that is always interpreted in base 10 (decimal). A repeat count may also be specified as an expression enclosed in square brackets preceded by a dollar sign ($[ ]). A string argument must be enclosed in double- quotes (" "). No blanks are necessary between format argu- ments. The formatting dcmds are: / Display data from the target's virtual address space starting at the virtual address specified by dot. \ Display data from the target's physical address space starting at the physical address specified by dot. ? Display data from the target's primary object file starting at the object file location corresponding to the virtual address specified by dot. = Display the value of dot itself in each of the speci- fied data formats. The = dcmd is therefore useful for converting between bases and performing arithmetic. In addition to dot, mdb keeps track of another global value called the increment. The increment represents the distance between dot and the address following all the data read by the last formatting dcmd. For example, if a formatting dcmd is executed with dot equal to address A, and displays a 4- byte integer, then after this dcmd completes, dot is still A, but the increment is set to 4. The + character (described under Arithmetic Expansion above) would now evaluate to the value A + 4, and could be used to reset dot to the address of the next data object for a subsequent dcmd. SunOS 5.8 Last change: 14 Sep 1999 14 User Commands mdb(1) Most format characters increase the value of the increment by the number of bytes corresponding to the size of the data format, shown in the table. The table of format characters can be displayed from within mdb using the ::formats dcmd. The format characters are: + increment dot by the count (variable size) - decrement dot by the count (variable size) B hexadecimal int (1 byte) C character using C character notation (1 byte) D decimal signed int (4 bytes) E decimal unsigned long long (8 bytes) F double (8 bytes) G octal unsigned long long (8 bytes) H swap bytes and shorts (4 bytes) I address and disassembled instruction (variable size) J hexadecimal long long (8 bytes) K hexadecimal uintptr_t (4 or 8 bytes) O octal unsigned int (4 bytes) P symbol (4 or 8 bytes) Q octal signed int (4 bytes) S string using C string notation (variable size) U decimal unsigned int (4 bytes) V decimal unsigned int (1 byte) W default radix unsigned int (4 bytes) X hexadecimal int (4 bytes) Y decoded time32_t (4 bytes) Z hexadecimal long long (8 bytes) ^ decrement dot by increment * count (variable size) a dot as symbol+offset b octal unsigned int (1 byte) c character (1 byte) d decimal signed short (2 bytes) e decimal signed long long (8 bytes) f float (4 bytes) g octal signed long long (8 bytes) h swap bytes (2 bytes) i disassembled instruction (variable size) n newline o octal unsigned short (2 bytes) p symbol (4 or 8 bytes) q octal signed short (2 bytes) r whitespace s raw string (variable size) t horizontal tab u decimal unsigned short (2 bytes) v decimal signed int (1 byte) w default radix unsigned short (2 bytes) x hexadecimal short (2 bytes) y decoded time64_t (8 bytes) SunOS 5.8 Last change: 14 Sep 1999 15 User Commands mdb(1) The /, \, and ? formatting dcmds can also be used to write to the target's virtual address space, physical address space, or object file by specifying one of the following modifiers as the first format character, and then specifying a list of words that are either immediate values or expres- sions enclosed in square brackets preceded by a dollar sign ($[ ]). The write modifiers are: v, w Write the lowest 2 bytes of the value of each expres- sion to the target beginning at the location specified by dot. W Write the lowest 4 bytes of the value of each expres- sion to the target beginning at the location specified by dot. Z Write the complete 8 bytes of the value of each expression to the target beginning at the location specified by dot. The /, \, and ? formatting dcmds can also be used to search for a particular integer value in the target's virtual address space, physical address space, and object file, respectively, by specifying one of the following modifiers as the first format character, and then specifying a value and optional mask. The value and mask are each specified as either immediate values or expressions enclosed in square brackets preceded by a dollar sign. If only a value is specified, mdb reads integers of the appropriate size and stops at the address containing the matching value. If a value V and mask M are specified, mdb reads integers of the appropriate size and stops at the address containing a value X where (X & M) == V. At the completion of the dcmd, dot is updated to the address containing the match. If no match is found, dot is left at the last address that was read. The search modifiers are: l Search for the specified 2-byte value. L Search for the specified 4-byte value. M Search for the specified 8-byte value. Note that for both user and kernel targets, an address space is typically composed of a set of discontiguous segments. It is not legal to read from an address that does not have a corresponding segment. If a search reaches a segment boun- dary without finding a match, it will abort when the read past the end of the segment boundary fails. SunOS 5.8 Last change: 14 Sep 1999 16 User Commands mdb(1) Builtin dcmds mdb provides a set of builtin dcmds that are always defined. Some of these dcmds are only applicable to certain targets: if a dcmd is not applicable to the current target, it will fail and print a message indicating "command is not sup- ported by current target". In many cases, mdb provides a mnemonic equivalent (::identifier) for the legacy adb(1) dcmd names. For example, ::quit is provided as the equivalent of $q. Programmers who are experienced with adb(1) or who appreciate brevity or arcana may prefer the $ or : forms of the builtins. Programmers who are new to mdb may prefer the more verbose :: form. The builtins are shown in alphabetical order. If a $ or : form has a ::identifier equivalent, it is shown underneath the ::identifier form. The builtin dcmds are: > variable-name >/modifier/ variable-name Assign the value of dot to the specified named vari- able. Some variables are read-only and may not be modified. If the > is followed by a modifier charac- ter surrounded by / /, then the value is modified as part of the assignment. The modifier characters are: c unsigned char quantity (1-byte) s unsigned short quantity (2-byte) i unsigned int quantity (4-byte) l unsigned long quantity (4-byte in 32-bit, 8-byte in 64-bit) Notice that these operators do not perform a cast; they instead fetch the specified number of low-order bytes (on little-endian architectures) or high-order bytes (big-endian architectures). Modifiers are provided for backwards compa- tibility; the mdb */modifier/ and %/modifier/ syntax should be used instead. $< macro-name Read and execute commands from the specified macro file. The filename may be given as an absolute or relative path. If the filename is a simple name (that is, if it does not contain a '/'), mdb will search for it in the macro file include path. If another macro file is currently being processed, this file is closed and replaced with the new file. $<< macro-name SunOS 5.8 Last change: 14 Sep 1999 17 User Commands mdb(1) Read and execute commands from the specified macro file (as with $<), but do not close the current open macro file. $? Print the process-ID and current signal of the target if it is a user process or core file, and then print the general register set of the representative thread. [ address ] $C [ count ] Print a C stack backtrace, including stack frame pointer information. If the dcmd is preceded by an explicit address, a backtrace beginning at this vir- tual memory address is displayed. Otherwise the stack of the representative thread is displayed. If an optional count value is given as an argument, no more than count arguments are displayed for each stack frame in the output. [ base ] $d Get or set the default output radix. If the dcmd is preceded by an explicit expression, the default output radix is set to the given base; otherwise the current radix is printed in base 10 (decimal). The default radix is base 16 (hexadecimal). $e Print a list of all known external (global) symbols of type object or function, the value of the symbol, and the first 4 (32-bit mdb) or 8 (64-bit mdb) bytes stored at this location in the target's virtual address space. The ::nm dcmd provides more flexible options for displaying symbol tables. $P prompt-string Set the prompt to the specified prompt-string. The default prompt is '> '. The prompt can also be set using ::set -P or the -P command-line option distance $s Get or set the symbol matching distance for address- to-symbol-name conversions. The symbol matching dis- tance modes are discussed along with the -s command- line option under OPTIONS, below. The symbol matching distance may also be modified using the ::set -s option. If no distance is specified, the current set- ting is displayed. $v Print a list of the named variables that have non-zero values. The ::vars dcmd provides other options for listing variables. width $w Set the output page width to the specified value. SunOS 5.8 Last change: 14 Sep 1999 18 User Commands mdb(1) Typically, this command is not necessary as mdb queries the terminal for its width and handles resize events. $W Re-open the target for writing, as if mdb had been executed with the -w option on the command line. Write mode can also be enabled with the ::set -w option. [ pid ] ::attach [ core | pid ] [ pid ] :A [ core | pid ] If the user process target is active, attach to and debug the specified process-ID or core file. The core file pathname should be specified as a string argu- ment. The process-ID may be specified as the string argument, or as the value of the expression preceding the dcmd. Recall that the default base is hexadecimal, so decimal PIDs obtained using pgrep(1) or ps(1)) should be preceded with "0t" when specified as expres- sions. ::cat filename ... Concatenate and display files. Each filename may specified as a relative or absolute pathname. The file contents will be printed to standard output, but will not be passed to the output pager. This dcmd is intended to be used with the | operator; the program- mer can initiate a pipeline using a list of addresses stored in an external file. address ::context address $p Context switch to the specified process. A context switch operation is only valid when using the kernel target. The process context is specified using the address of its proc structure in the kernel's virtual address space. The special context address "0" is used to denote the context of the kernel itself. mdb can only perform a context switch when examining a crash dump if the dump contains all physical memory pages (as opposed to just kernel pages). The kernel crash dump facility can be configured to dump all pages using dumpadm(1M). When the user requests a context switch from the ker- nel target, mdb constructs a new target representing the specified user process. Once the switch occurs, the new target interposes its dcmds at the global level: thus the / dcmd will now format and display data from the virtual address space of the user pro- cess, the ::mappings dcmd will display the mappings in SunOS 5.8 Last change: 14 Sep 1999 19 User Commands mdb(1) the address space of the user process, and so on. The kernel target can be restored by executing 0::context. ::dcmds List the available dcmds and print a brief description for each one. [ address ] ::dis [ -fw ] [ -n count ] [ address ] Disassemble starting at or around the address speci- fied by the final argument, or the current value of dot. If the address matches the start of a known func- tion, the entire function is disassembled; otherwise a "window" of instructions before and after the speci- fied address is printed in order to provide context. By default, instructions are read from the target's virtual address space; if the -f option is present, instructions are read from the target's object file instead. The -w option can be used to force "window"- mode, even if the address is the start of a known function. The size of the window defaults to ten instructions; the number of instructions can be speci- fied explicitly using the -n option. ::disasms List the available disassembler modes. When a target is initialized, mdb will attempt to select the appropriate disassembler mode. The user can change the mode to any of the modes listed using the ::dismode dcmd. ::dismode [ mode ] $V [ mode ] Get or set the disassembler mode. If no argument is specified, print the current disassembler mode. If a mode argument is specified, switch the disassembler to the specified mode. The list of available disassem- blers can be displayed using the ::disasms dcmd. ::dmods [ -l ] [ module-name ] List the loaded debugger modules. If the -l option is specified, the list of the dcmds and walkers associ- ated with each dmod is printed below its name. The output can be restricted to a particular dmod by specifying its name as an additional argument. ::dump Print a hexadecimal and ASCII memory dump of the 16- byte aligned region of virtual memory containing the address specified by dot. If a repeat count is speci- fied for ::dump, this is interpreted as a number of bytes to dump rather than a number of iterations. SunOS 5.8 Last change: 14 Sep 1999 20 User Commands mdb(1) ::echo [ string | value ... ] Print the arguments separated by blanks and terminated by a NEWLINE to standard output. Expressions enclosed in $[ ] will be evaluated to a value and printed in the default base. ::eval command Evaluate and execute the specified string as a com- mand. If the command contains metacharacters or whi- tespace, it should be enclosed in double or single quotes. ::files $f Print a list of the known source files (symbols of type STT_FILE present in the various target symbol tables). ::fpregs $x, $X, $y, $Y Print the floating-point register set of the represen- tative thread. ::formats List the available output format characters for use with the /, \, ?, and = formatting dcmds. The formats and their use is described under Formatting dcmds, above. ::grep command Evaluate the specified command string, and then print the old value of dot if the new value of dot is non- zero. If the command contains whitespace or metachar- acters, it must be quoted. The ::grep dcmd can be used in pipelines to filter a list of addresses. ::help [ dcmd-name ] With no arguments, the ::help dcmd prints a brief overview of the help facilities available in mdb. If a dcmd-name is specified, mdb will print a usage summary for that dcmd. ::load module-name Load the specified dmod. The module name may be given as an absolute or relative path. If module-name is a simple name (that is, does not contain a '/'), mdb will search for it in the module library path. Modules with conflicting names may not be loaded; the existing module must be unloaded first. ::log [ -d | [ -e ] filename ] SunOS 5.8 Last change: 14 Sep 1999 21 User Commands mdb(1) $> [ filename ] Enable or disable the output log. mdb provides an interactive logging facility where both the input com- mands and standard output can be logged to a file while still interacting with the user. The -e option enables logging to the specified file, or re-enables logging to the previous log file if no filename is given. The -d option disables logging. If the $> dcmd is used, logging is enabled if a filename argument is specified; otherwise, logging is disabled. If the specified log file already exists, mdb appends any new log output to the file. ::map command Map the value of dot to a corresponding value using the command specified as a string argument, and then print the new value of dot. If the command contains whitespace or metacharacters, it must be quoted. The ::map dcmd can be used in pipelines to transform the list of addresses into a new list of addresses. [ address ] ::mappings [ name ] [ address ] $m [ name ] Print a list of each mapping in the target's virtual address space, including the address, size, and description of each mapping. If the dcmd is preceded by an address, mdb will only show the mapping that contains the given address. If a string name argument is given, mdb will only show the mapping matching that description. ::nm [ -DPdghnopuvx ] [ object ] Print the symbol tables associated with the current target. If an object name argument is specified, only the symbol table for this load object is displayed. The ::nm dcmd also recognizes the following options: -D Print .dynsym (dynamic symbol table) instead of .symtab. -P Print the private symbol table instead of .sym- tab. -d Print value and size fields in decimal. -g Print only global symbols. -h Suppress the header line. -n Sort symbols by name. SunOS 5.8 Last change: 14 Sep 1999 22 User Commands mdb(1) -o Print value and size fields in octal. -p Print symbols as a series of ::nmadd commands. This option can be used with -P to produce a macro file that can be subsequently read into the debugger with $<. -u Print only undefined symbols. -v Sort symbols by value. -x Print value and size fields in hexadecimal. value ::nmadd [ -fo ] [ -e end ] [ -s size ] name Add the specified symbol name to the private symbol table. mdb provides a private, configurable symbol table that can be used to interpose on the target's symbol table, as described under Symbol Name Resolu- tion above. The ::nmadd dcmd also recognizes the fol- lowing options: -e Set the size of the symbol to end - value. -f Set the type of the symbol to STT_FUNC. -o Set the type of the symbol to STT_OBJECT. -s Set the size of the symbol to size. ::nmdel name Delete the specified symbol name from the private sym- bol table. ::objects Print a map of the target's virtual address space, showing only those mappings that correspond to the primary mapping (usually the text section) of each of the known load objects. ::quit $q Quit the debugger. ::regs $r Print the general-purpose register set of the representative thread. ::release SunOS 5.8 Last change: 14 Sep 1999 23 User Commands mdb(1) :R Release the previously attached process or core file. path ::set [ -wF ] [ +/-o option ] [ - s distance ] [ - I path ] [ -L ] [ -P prompt ]" 6 Get or set miscellaneous debugger properties. If no options are specified, the current set of debugger properties is displayed. The ::set dcmd recognizes the following options: -F Forcibly take over the next user process that ::attach is applied to, as if mdb had been exe- cuted with the -F option on the command line. -I Set the default path for locating macro files. The path argument may contain any of the special tokens described for the -I command-line option under OPTIONS below. -L Set the default path for locating debugger modules. The path argument may contain any of the special tokens described for the -I command-line option under OPTIONS below. -o Enable the specified debugger option. If the +o form is used, the option is disabled. The option strings are described along with the -o command-line option under OPTIONS below. -P Set the command prompt to the specified prompt string. -s Set the symbol matching distance to the speci- fied distance. Refer to the description of the -s command-line option under OPTIONS below for more information. -w Re-open the target for writing, as if mdb had been executed with the -w option on the command line. [ address ] ::stack [ count ] [ address ] $c [ count ] Print a C stack backtrace. If the dcmd is preceded by an explicit address, a backtrace beginning at this virtual memory address is displayed. Otherwise the stack of the representative thread is displayed. If an optional count value is given as an argument, no more than count arguments are displayed for each stack SunOS 5.8 Last change: 14 Sep 1999 24 User Commands mdb(1) frame in the output. ::status Print a summary of information related to the current target. ::typeset [+/-t] variable-name ... Set attributes for named variables. If one or more variable names are specified, they are defined and set to the value of dot. If the -t option is present, the user-defined tag associated with each variable is set. If the +t option is present, the tag is cleared. If no variable names are specified, the list of variables and their values is printed. ::unload module-name Unload the specified dmod. The list of active dmods may be printed using the ::dmods dcmd. Builtin modules may not be unloaded. Modules that are busy (that is, provide dcmds that are currently executing) may not be unloaded. ::unset variable-name ... Unset (remove) the specified variable(s) from the list of defined variables. Some variables are exported by mdb are marked as persistent, and may not be unset by the user. ::vars [-npt] Print a listing of named variables. If the -n option is present, the output is restricted to variables that currently have non-zero values. If the -p option is present, the variables are printed in a form suitable for re-processing by the debugger using the $< dcmd. This option can be used to record the variables to a macro file and then restore these values later. If the -t option is present, only the tagged variables are printed. Variables can be tagged using the -t option of the ::typeset dcmd. ::version Print the debugger version number. address ::vtop Print the physical address mapping for the specified virtual address, if possible. The ::vtop dcmd is only available when examining a kernel target, or when exa- mining a user process inside a kernel crash dump (after a ::context dcmd has been issued). [ address ] ::walk walker-name [ variable-name ] Walk through the elements of a data structure using SunOS 5.8 Last change: 14 Sep 1999 25 User Commands mdb(1) the specified walker. The available walkers can be listed using the ::walkers dcmd. Some walkers operate on a global data structure and do not require a start- ing address. For example, walk the list of proc struc- tures in the kernel. Other walkers operate on a specific data structure whose address must be speci- fied explicitly. For example, given a pointer to an address space, walk the list of segments. When used interactively, the ::walk dcmd will print the address of each element of the data structure in the default base. The dcmd can also be used to provide a list of addresses for a pipeline. The walker name may use the backquote (`) scoping operator described under dcmd and Walker Name Resolution, above. If the optional variable-name is specified, the specified variable will be assigned the value returned at each step of the walk when mdb invokes the next stage of the pipe- line. ::walkers List the available walkers and print a brief descrip- tion for each one. ::whence [-v] name ... ::which [-v] name ... Print the dmod that exports the specified dcmds and walkers. These dcmds can be used to determine which dmod is currently providing the global definition of the given dcmd or walker. Refer to the section on dcmd and Walker Name Resolution above for more information on global name resolution. The -v option will cause the dcmd to print the alternate definitions of each dcmd and walker in order of precedence. ::xdata List the external data buffers exported by the current target. External data buffers represent information associated with the target that can not be accessed through standard target facilities (that is, an address space, symbol table, or register set). These buffers may be consumed by dcmds; for more informa- tion, refer to the Solaris Modular Debugger Guide.

OPTIONS

The following options are supported: -A Disables automatic loading of mdb modules. By default, mdb will attempt to load debugger modules correspond- ing to the active shared libraries in a user process or core file, or to the loaded kernel modules in the live operating system or an operating system crash SunOS 5.8 Last change: 14 Sep 1999 26 User Commands mdb(1) dump. -F Forcibly takes over the specified user process, if necessary. By default, mdb will refuse to attach to a user process that is already under the control of another debugging tool, such as truss(1). With the -F option, mdb will attach to these processes anyway. This may produce unexpected interactions between mdb and the other tools attempting to control the process. -I Sets default path for locating macro files. Macro files are read using the $< or $<< dcmds. The path is a sequence of directory names delimited by colon (:) characters. The -I include path and -L library path (see below) may also contain any of the following tokens: %i Expands to the current instruction set architecture (ISA) name ('sparc', 'sparcv9', or 'i386'). %o Expands to the old value of the path being modified. This is useful for appending or prepending directories to an existing path. %p Expands to the current platform string (either uname -i or the platform string stored in the process core file or crash dump). %r Expands to the pathname of the root directory. An alternate root directory may be specified using the -R option. If no -R option is present, the root directory is derived dynamically from the path to the mdb exe- cutable itself. For example, if /bin/mdb is executed, the root directory will be /. If /net/hostname/bin/mdb were executed, the root direc- tory would be derived as /net/hostname. %t Expands to the name of the current target. This will either be the literal string 'proc' (a user process or user process core file), or 'kvm' (a kernel crash dump or the live operating system). The default include path for 32-bit mdb is: %r/usr/platform/%p/lib/adb:%r/usr/lib/adb The default include path for 64-bit mdb is: %r/usr/platform/%p/lib/adb/%i:%r/usr/lib/adb/%i SunOS 5.8 Last change: 14 Sep 1999 27 User Commands mdb(1) -k Forces kernel debugging mode. By default, mdb will attempt to infer whether the object and core file operands refer to a user executable and core dump, or to a pair of operating system crash dump files. The -k option forces mdb to assume these files are operating system crash dump files. If no object or core operand is specified, but the -k option is specified, mdb will default to an object file of /dev/ksyms and a core file of /dev/kmem. Access to /dev/kmem is restricted to group sys. -L Sets default path for locating debugger modules. Modules are loaded automatically on startup or using the ::load dcmd. The path is a sequence of directory names delimited by colon (:) characters. The -L library path may also contain any of the tokens shown for -I above. -m Disables demand-loading of kernel module symbols. By default, mdb will process the list of loaded kernel modules and perform demand loading of per-module sym- bol tables. If the -m option is specified, mdb will not attempt to process the kernel module list or pro- vide per-module symbol tables. As a result, mdb modules corresponding to active kernel modules will not be loaded on startup. -M Preloads all kernel module symbols. By default, mdb performs demand-loading for kernel module symbols: the complete symbol table for a module is read when an address is that module's text or data section is referenced. With the -M option, mdb will load the com- plete symbol table of all kernel modules during startup. -o option Enables the specified debugger option. If the +o form of the option is used, the specified option is dis- abled. Unless noted below, each option is off by default. mdb recognizes the following option argu- ments: adb Enable stricter adb(1) compatibility. The prompt will be set to the empty string and many mdb features, such as the output pager, will be dis- abled. follow_child The debugger will follow the child process if a fork(2)) system call occurs. By default, the debugger remains attached to the original target process (the parent). SunOS 5.8 Last change: 14 Sep 1999 28 User Commands mdb(1) ignoreeof The debugger will not exit when an EOF sequence (^D) is entered at the terminal. The ::quit dcmd must be used to quit. pager The output pager will be enabled (default). repeatlast If a NEWLINE is entered as the complete command at the terminal, mdb will repeat the previous command with the current value of dot. This option is implied by -o adb. -p pid Attach to and stop the specified process-id. mdb will use the /proc/pid/object/a.out file as the executable file pathname. -P Sets the command prompt. The default prompt is '> '. -R Sets root directory for pathname expansion. By default, the root directory is derived from the path- name of the mdb executable itself. The root directory is substituted in place of the %r token during path- name expansion. -s distance Sets the symbol matching distance for address-to- symbol-name conversions to the specified distance. By default, mdb sets the distance to zero, which enables a smart-matching mode. Each ELF symbol table entry includes a value V and size S, representing the size of the function or data object in bytes. In smart mode, mdb matches an address A with the given symbol if A is in the range [ V, V + S ). If any non-zero distance is specified, the same algorithm is used, but S in the expression above is always the specified absolute distance and the symbol size is ignored. -S Suppresses processing of the user's ~/.mdbrc file. By default, mdb will read and process the macro file .mdbrc if one is present in the user's home directory, as defined by $HOME. If the -S option is present, this file will not be read. -u Forces user debugging mode. By default, mdb will attempt to infer whether the object and core file operands refer to a user executable and core dump, or to a pair of operating system crash dump files. The -u option forces mdb to assume these files are not operating system crash dump files. SunOS 5.8 Last change: 14 Sep 1999 29 User Commands mdb(1) -V Sets disassembler version. By default, mdb will attempt to infer the appropriate disassembler version for the debug target. The disassembler can be set explicitly using the -V option. The ::disasms dcmd lists the available disassembler versions. -w Opens the specified object and core files for writing. -y Sends explicit terminal initialization sequences for tty mode. Some terminals, such as require explicit initialization sequences to switch into a tty mode. Without this initialization sequence, terminal features such as standout mode may not be available to mdb.

OPERANDS

The following operands are supported: object Specifies an ELF format object file to examine. mdb provides the ability to examine and edit ELF format executables (ET_EXEC), ELF dynamic library files (ET_DYN), ELF relocatable object files (ET_REL), and operating system unix.X symbol table files. core Specifies an ELF process core file (ET_CORE), or an operating system crash dump vmcore.X file. If an ELF core file operand is provided without a corresponding object file, mdb will attempt to infer the name of the executable file that produced the core using several different algorithms. If no executable is found, mdb will still execute, but some symbol information may be unavailable. suffix Specifies the numerical suffix representing a pair of operating system crash dump files. For example, if the suffix is '3', mdb infers that it should examine the files 'unix.3' and 'vmcore.3'. The string of digits will not be interpreted as a suffix if an actual file of the same name is present in the current directory.

EXIT STATUS

The following exit values are returned: 0 Debugger completed execution successfully. 1 A fatal error occurred. 2 Invalid command line options were specified. SunOS 5.8 Last change: 14 Sep 1999 30 User Commands mdb(1)

ENVIRONMENT VARIABLES

HISTSIZE This variable is used to determine the maximum length of the command history list. If this variable is not present, the default length is 128. HOME This variable is used to determine the pathname of the user's home directory, where a .mdbrc file may reside. If this variable is not present, no .mdbrc processing will occur. SHELL This variable is used to determine the pathname of the shell used to process shell escapes requested using the ! meta-character. If this variable is not present, /bin/sh is used.

FILES

$HOME/.mdbrc User mdb initialization file. The .mdbrc file, if present, is processed after the debug target has been initialized, but before module auto-loading is per- formed or any commands have been read from standard input. /dev/kmem Kernel virtual memory image device. This device spe- cial file is used as the core file when examining the live operating system. /dev/ksyms Kernel symbol table device. This device special file is used as the object file when examining the live operating system. /proc/pid/* Process information files that are read when examining and controlling user processes. /usr/lib/adb /usr/platform/platform-name/lib/adb Default directories for macro files that are read with the $< and $<< dcmds. platform-name is the name of the platform, derived either from information in a core file or crash dump, or from the current machine as if by uname -i (see uname(1)). /usr/lib/mdb /usr/platform/platform-name/lib/mdb Default directories for debugger modules that are loaded using the ::load dcmds. platform-name is the SunOS 5.8 Last change: 14 Sep 1999 31 User Commands mdb(1) name of the platform, derived either from information in a core file or crash dump, or from the current machine as if by uname -i (see uname(1)).

ATTRIBUTES

See attributes(5) for descriptions of the following attri- butes: ____________________________________________________________ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | | ____________________________|_____________________________|_ | Availability | SUNWmdb (32-bit), SUNWmdbx| | | (64-bit) | |_____________________________|_____________________________| | Interface Stability | Evolving | |_____________________________|_____________________________|

SEE ALSO

adb(1), gcore(1), proc(1), pgrep(1), ps(1), stty(1), truss(1), uname(1), coreadm(1M), dumpadm(1M), savecore(1M), fork(2), _lwp_self(2), pipe(2), elf(3ELF), libthread(3THR), libthread_db(3LIB), signal(3C), signal(3HEAD), thr_self(3THR), core(4), libkvm(4), proc(4), attributes(5), largefile(5), ksyms(7D), mem(7D) Linker and Libraries Guide Solaris Modular Debugger Guide

WARNINGS

Use of the Error Recovery Mechanism The debugger and its dmods execute in the same address space, and thus it is quite possible that a buggy dmod can cause mdb to dump core or otherwise misbehave. The mdb resume capability, described above under Signal Handling, provides a limited recovery mechanism for these situations. However, it is not possible for mdb to know definitively whether the dmod in question has corrupted only its own state, or the debugger's global state. Therefore a resume operation cannot be guaranteed to be safe, or to prevent a subsequent crash of the debugger. The safest course of action following a resume is to save any important debug information, and then quit and restart the debugger. Use of the Debugger to Modify the Live Operating System The use of the debugger to modify (that is, write to) the address space of live running operating system is extremely dangerous, and may result in a system panic in the event the user damages a kernel data structure. SunOS 5.8 Last change: 14 Sep 1999 32 User Commands mdb(1)

NOTES

Limitations on Examining Process Core Files mdb does not provide support for examining process core files that were generated by a release of Solaris preceding Solaris 2.6. If a core file from one operating system release is examined on a different operating system release, the run-time link-editor debugging interface (librtld_db) may not be able to initialize. In this case, symbol informa- tion for shared libraries will not be available. Further- more, since shared mappings are not present in user core files, the text section and read-only data of shared libraries may not match the data that was present in the process at the time it dumped core. Core files from Solaris Intel systems may not be examined on Solaris SPARC systems, and vice-versa. Limitations on Examining Crash Dump Files Crash dumps from Solaris 7 and earlier releases may only be examined with the aid of the libkvm from the corresponding operating system release. If a crash dump from one operating system release is examined using the dmods from a different operating system release, changes in the kernel implementa- tion may prevent some dcmds or walkers from working prop- erly. mdb will issue a warning message if it detects this condition. Crash dumps from Solaris Intel systems may not be examined on Solaris SPARC systems, and vice-versa. Relationship Between 32-bit and 64-bit Debugger mdb provides support for debugging both 32-bit and 64-bit programs. Once it has examined the target and determined its data model, mdb will automatically re-execute the mdb binary that has the same data model as the target, if necessary. This approach simplifies the task of writing debugger modules, because the modules that are loaded will use the same data model as the primary target. Only the 64-bit debugger may be used to debug 64-bit target programs. The 64-bit debugger can only be used on a system that is running the 64-bit operating environment. Developer Information The Solaris Modular Debugger Guide provides a more detailed description of mdb features, as well as information for debugger module developers. SunOS 5.8 Last change: 14 Sep 1999 33