Debugging with GDB - GDB/MI Data Manipulation

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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 section 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 section 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 then 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)

Go to the first, previous, next, last section, table of contents.

GDB/MI Data Manipulation

The -data-disassemble Command

Synopsis

Result

GDB Command

Example

The -data-evaluate-expression Command

Synopsis

GDB Command

Example

The -data-list-changed-registers Command

Synopsis

GDB Command

Example

The -data-list-register-names Command

Synopsis

GDB Command

Example

The -data-list-register-values Command

Synopsis

GDB Command

Example

The -data-read-memory Command

Synopsis

GDB Command

Example

The -display-delete Command

Synopsis

GDB Command

Example

The -display-disable Command

Synopsis

GDB Command

Example

The -display-enable Command

Synopsis

GDB Command

Example

The -display-insert Command

Synopsis

GDB Command

Example

The -display-list Command

Synopsis

GDB Command

Example

The -environment-cd Command

Synopsis

GDB Command

Example

The -environment-directory Command

Synopsis

GDB Command

Example

The -environment-path Command

Synopsis

GDB Command

Example

The -environment-pwd Command

Synopsis

GDB command

Example

The `-data-disassemble` Command

The `-data-evaluate-expression` Command

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

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

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

The `-data-read-memory` Command

The `-display-delete` Command

The `-display-disable` Command

The `-display-enable` Command

The `-display-insert` Command

The `-display-list` Command

The `-environment-cd` Command

The `-environment-directory` Command

The `-environment-path` Command

The `-environment-pwd` Command