Debugging with GDB

Node:GDB/MI Data Manipulation, Next:GDB/MI Program Control, Previous:GDB/MI Breakpoint Table Commands, Up:GDB/MI

### GDB/MI Data Manipulation

This section describes the GDB/MI commands that manipulate data: examine memory and registers, evaluate expressions, etc.

#### The `-data-disassemble` Command

##### Synopsis

          -data-disassemble
             [ -s start-addr -e end-addr ]
           | [ -f filename -l linenum [ -n lines ] ]
           -- mode

Where:

``start-addr``
  is the beginning address (or `$pc`)
``end-addr``
  is the end address
``filename``
  is the name of the file to disassemble
``linenum``
  is the line number to disassemble around
``lines``
  is the the number of disassembly lines to be produced. If it is -1, the whole function will be disassembled, in case no end-addr is specified. If end-addr is specified as a non-zero value, and lines is lower than the number of disassembly lines between start-addr and end-addr, only lines lines are displayed; if lines is higher than the number of lines between start-addr and end-addr, only the lines up to end-addr are displayed.
``mode``
  is either 0 (meaning only disassembly) or 1 (meaning mixed source and disassembly).

##### Result

The output for each instruction is composed of four fields:

- Address
- Func-name
- Offset
- Instruction

Note that whatever included in the instruction field, is not manipulated directely by GDB/MI, i.e. it is not possible to adjust its format.

##### GDB Command

There's no direct mapping from this command to the CLI.

##### Example

Disassemble from the current value of `$pc` to `$pc + 20`:

         (gdb)
         -data-disassemble -s $pc -e "$pc + 20" -- 0
         ^done,
         asm_insns=[
         {address="0x000107c0",func-name="main",offset="4",
         inst="mov  2, %o0"},
         {address="0x000107c4",func-name="main",offset="8",
         inst="sethi  %hi(0x11800), %o2"},
         {address="0x000107c8",func-name="main",offset="12",
         inst="or  %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"},
         {address="0x000107cc",func-name="main",offset="16",
         inst="sethi  %hi(0x11800), %o2"},
         {address="0x000107d0",func-name="main",offset="20",
         inst="or  %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"}]
         (gdb)

Disassemble the whole `main` function. Line 32 is part of `main`.

         -data-disassemble -f basics.c -l 32 -- 0
         ^done,asm_insns=[
         {address="0x000107bc",func-name="main",offset="0",
         inst="save  %sp, -112, %sp"},
         {address="0x000107c0",func-name="main",offset="4",
         inst="mov   2, %o0"},
         {address="0x000107c4",func-name="main",offset="8",
         inst="sethi %hi(0x11800), %o2"},
         [...]
         {address="0x0001081c",func-name="main",offset="96",inst="ret "},
         {address="0x00010820",func-name="main",offset="100",inst="restore "}]
         (gdb)

Disassemble 3 instructions from the start of `main`:

         (gdb)
         -data-disassemble -f basics.c -l 32 -n 3 -- 0
         ^done,asm_insns=[
         {address="0x000107bc",func-name="main",offset="0",
         inst="save  %sp, -112, %sp"},
         {address="0x000107c0",func-name="main",offset="4",
         inst="mov  2, %o0"},
         {address="0x000107c4",func-name="main",offset="8",
         inst="sethi  %hi(0x11800), %o2"}]
         (gdb)

Disassemble 3 instructions from the start of `main` in mixed mode:

         (gdb)
         -data-disassemble -f basics.c -l 32 -n 3 -- 1
         ^done,asm_insns=[
         src_and_asm_line={line="31",
         file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
           testsuite/gdb.mi/basics.c",line_asm_insn=[
         {address="0x000107bc",func-name="main",offset="0",
         inst="save  %sp, -112, %sp"}]},
         src_and_asm_line={line="32",
         file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
           testsuite/gdb.mi/basics.c",line_asm_insn=[
         {address="0x000107c0",func-name="main",offset="4",
         inst="mov  2, %o0"},
         {address="0x000107c4",func-name="main",offset="8",
         inst="sethi  %hi(0x11800), %o2"}]}]
         (gdb)

#### The `-data-evaluate-expression` Command

##### Synopsis

          -data-evaluate-expression expr

Evaluate expr as an expression. The expression could contain an inferior function call. The function call will execute synchronously. If the expression contains spaces, it must be enclosed in double quotes.

##### GDB Command

The corresponding GDB commands are `print`, `output`, and `call`. In `gdbtk` only, there's a corresponding `gdb_eval` command.

##### Example

In the following example, the numbers that precede the commands are the tokens described in GDB/MI Command Syntax. Notice how GDB/MI returns the same tokens in its output.

         211-data-evaluate-expression A
         211^done,value="1"
         (gdb)
         311-data-evaluate-expression &A
         311^done,value="0xefffeb7c"
         (gdb)
         411-data-evaluate-expression A+3
         411^done,value="4"
         (gdb)
         511-data-evaluate-expression "A + 3"
         511^done,value="4"
         (gdb)

#### The `-data-list-changed-registers` Command

##### Synopsis

          -data-list-changed-registers

Display a list of the registers that have changed.

##### GDB Command

GDB doesn't have a direct analog for this command; `gdbtk` has the corresponding command `gdb_changed_register_list`.

##### Example

On a PPC MBX board:

         (gdb)
         -exec-continue
         ^running

         (gdb)
         *stopped,reason="breakpoint-hit",bkptno="1",frame={func="main",
         args=[],file="try.c",line="5"}
         (gdb)
         -data-list-changed-registers
         ^done,changed-registers=["0","1","2","4","5","6","7","8","9",
         "10","11","13","14","15","16","17","18","19","20","21","22","23",
         "24","25","26","27","28","30","31","64","65","66","67","69"]
         (gdb)

#### The `-data-list-register-names` Command

##### Synopsis

          -data-list-register-names [ ( regno )+ ]

Show a list of register names for the current target. If no arguments are given, it shows a list of the names of all the registers. If integer numbers are given as arguments, it will print a list of the names of the registers corresponding to the arguments. To ensure consistency between a register name and its number, the output list may include empty register names.

##### GDB Command

GDB does not have a command which corresponds to `-data-list-register-names`. In `gdbtk` there is a corresponding command `gdb_regnames`.

##### Example

For the PPC MBX board:

         (gdb)
         -data-list-register-names
         ^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7",
         "r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18",
         "r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29",
         "r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9",
         "f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20",
         "f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31",
         "", "pc","ps","cr","lr","ctr","xer"]
         (gdb)
         -data-list-register-names 1 2 3
         ^done,register-names=["r1","r2","r3"]
         (gdb)

#### The `-data-list-register-values` Command

##### Synopsis

          -data-list-register-values fmt [ ( regno )*]

Display the registers' contents. fmt is the format according to which the registers' contents are to be returned, followed by an optional list of numbers specifying the registers to display. A missing list of numbers indicates that the contents of all the registers must be returned.

Allowed formats for fmt are:

`x`
  Hexadecimal
`o`
  Octal
`t`
  Binary
`d`
  Decimal
`r`
  Raw
`N`
  Natural

##### GDB Command

The corresponding GDB commands are `info reg`, `info all-reg`, and (in `gdbtk`) `gdb_fetch_registers`.

##### Example

For a PPC MBX board (note: line breaks are for readability only, they don't appear in the actual output):

         (gdb)
         -data-list-register-values r 64 65
         ^done,register-values=[{number="64",value="0xfe00a300"},
         {number="65",value="0x00029002"}]
         (gdb)
         -data-list-register-values x
         ^done,register-values=[{number="0",value="0xfe0043c8"},
         {number="1",value="0x3fff88"},{number="2",value="0xfffffffe"},
         {number="3",value="0x0"},{number="4",value="0xa"},
         {number="5",value="0x3fff68"},{number="6",value="0x3fff58"},
         {number="7",value="0xfe011e98"},{number="8",value="0x2"},
         {number="9",value="0xfa202820"},{number="10",value="0xfa202808"},
         {number="11",value="0x1"},{number="12",value="0x0"},
         {number="13",value="0x4544"},{number="14",value="0xffdfffff"},
         {number="15",value="0xffffffff"},{number="16",value="0xfffffeff"},
         {number="17",value="0xefffffed"},{number="18",value="0xfffffffe"},
         {number="19",value="0xffffffff"},{number="20",value="0xffffffff"},
         {number="21",value="0xffffffff"},{number="22",value="0xfffffff7"},
         {number="23",value="0xffffffff"},{number="24",value="0xffffffff"},
         {number="25",value="0xffffffff"},{number="26",value="0xfffffffb"},
         {number="27",value="0xffffffff"},{number="28",value="0xf7bfffff"},
         {number="29",value="0x0"},{number="30",value="0xfe010000"},
         {number="31",value="0x0"},{number="32",value="0x0"},
         {number="33",value="0x0"},{number="34",value="0x0"},
         {number="35",value="0x0"},{number="36",value="0x0"},
         {number="37",value="0x0"},{number="38",value="0x0"},
         {number="39",value="0x0"},{number="40",value="0x0"},
         {number="41",value="0x0"},{number="42",value="0x0"},
         {number="43",value="0x0"},{number="44",value="0x0"},
         {number="45",value="0x0"},{number="46",value="0x0"},
         {number="47",value="0x0"},{number="48",value="0x0"},
         {number="49",value="0x0"},{number="50",value="0x0"},
         {number="51",value="0x0"},{number="52",value="0x0"},
         {number="53",value="0x0"},{number="54",value="0x0"},
         {number="55",value="0x0"},{number="56",value="0x0"},
         {number="57",value="0x0"},{number="58",value="0x0"},
         {number="59",value="0x0"},{number="60",value="0x0"},
         {number="61",value="0x0"},{number="62",value="0x0"},
         {number="63",value="0x0"},{number="64",value="0xfe00a300"},
         {number="65",value="0x29002"},{number="66",value="0x202f04b5"},
         {number="67",value="0xfe0043b0"},{number="68",value="0xfe00b3e4"},
         {number="69",value="0x20002b03"}]
         (gdb)

#### The `-data-read-memory` Command

##### Synopsis

          -data-read-memory [ -o byte-offset ]
            address word-format word-size
            nr-rows nr-cols [ aschar ]

where:

``address``
  An expression specifying the address of the first memory word to be read. Complex expressions containing embedded white space should be quoted using the C convention.
``word-format``
  The format to be used to print the memory words. The notation is the same as for GDB's `print` command (see Output formats).
``word-size``
  The size of each memory word in bytes.
``nr-rows``
  The number of rows in the output table.
``nr-cols``
  The number of columns in the output table.
``aschar``
  If present, indicates that each row should include an ASCII dump. The value of aschar is used as a padding character when a byte is not a member of the printable ASCII character set (printable ASCII characters are those whose code is between 32 and 126, inclusively).
``byte-offset``
  An offset to add to the address before fetching memory.

This command displays memory contents as a table of nr-rows by nr-cols words, each word being word-size bytes. In total, ``nr-rows`*` nr-cols`*` word-size`` bytes are read (returned as `total-bytes`). Should less than the requested number of bytes be returned by the target, the missing words are identified using `N/A`. The number of bytes read from the target is returned in `nr-bytes` and the starting address used to read memory in `addr`.

The address of the next/previous row or page is available in `next-row` and `prev-row`, `next-page` and `prev-page`.

##### GDB Command

The corresponding GDB command is `x`. `gdbtk` has `gdb_get_mem` memory read command.

##### Example

Read six bytes of memory starting at `bytes+6` but then offset by `-6` bytes. Format as three rows of two columns. One byte per word. Display each word in hex.

         (gdb)
         9-data-read-memory -o -6 -- bytes+6 x 1 3 2
         9^done,addr="0x00001390",nr-bytes="6",total-bytes="6",
         next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396",
         prev-page="0x0000138a",memory=[
         {addr="0x00001390",data=["0x00","0x01"]},
         {addr="0x00001392",data=["0x02","0x03"]},
         {addr="0x00001394",data=["0x04","0x05"]}]
         (gdb)

Read two bytes of memory starting at address `shorts + 64` and display as a single word formatted in decimal.

         (gdb)
         5-data-read-memory shorts+64 d 2 1 1
         5^done,addr="0x00001510",nr-bytes="2",total-bytes="2",
         next-row="0x00001512",prev-row="0x0000150e",
         next-page="0x00001512",prev-page="0x0000150e",memory=[
         {addr="0x00001510",data=["128"]}]
         (gdb)

Read thirty two bytes of memory starting at `bytes+16` and format as eight rows of four columns. Include a string encoding with `x` used as the non-printable character.

         (gdb)
         4-data-read-memory bytes+16 x 1 8 4 x
         4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32",
         next-row="0x000013c0",prev-row="0x0000139c",
         next-page="0x000013c0",prev-page="0x00001380",memory=[
         {addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"},
         {addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"},
         {addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"},
         {addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"},
         {addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"},
         {addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"},
         {addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"},
         {addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"}]
         (gdb)

#### The `-display-delete` Command

##### Synopsis

          -display-delete number

Delete the display number.

##### GDB Command

The corresponding GDB command is `delete display`.

##### Example

N.A.

#### The `-display-disable` Command

##### Synopsis

          -display-disable number

Disable display number.

##### GDB Command

The corresponding GDB command is `disable display`.

##### Example

N.A.

#### The `-display-enable` Command

##### Synopsis

          -display-enable number

Enable display number.

##### GDB Command

The corresponding GDB command is `enable display`.

##### Example

N.A.

#### The `-display-insert` Command

##### Synopsis

          -display-insert expression

Display expression every time the program stops.

##### GDB Command

The corresponding GDB command is `display`.

##### Example

N.A.

#### The `-display-list` Command

##### Synopsis

          -display-list

List the displays. Do not show the current values.

##### GDB Command

The corresponding GDB command is `info display`.

##### Example

N.A.

#### The `-environment-cd` Command

##### Synopsis

          -environment-cd pathdir

Set GDB's working directory.

##### GDB Command

The corresponding GDB command is `cd`.

##### Example

         (gdb)
         -environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
         ^done
         (gdb)

#### The `-environment-directory` Command

##### Synopsis

          -environment-directory pathdir

Add directory pathdir to beginning of search path for source files.

##### GDB Command

The corresponding GDB command is `dir`.

##### Example

         (gdb)
         -environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
         ^done
         (gdb)

#### The `-environment-path` Command

##### Synopsis

          -environment-path ( pathdir )+

Add directories pathdir to beginning of search path for object files.

##### GDB Command

The corresponding GDB command is `path`.

##### Example

         (gdb)
         -environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb
         ^done
         (gdb)

#### The `-environment-pwd` Command

##### Synopsis

          -environment-pwd

Show the current working directory.

##### GDB command

The corresponding GDB command is `pwd`.

##### Example

         (gdb)
         -environment-pwd
         ~Working directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb.
         ^done
         (gdb)