Gdb/GDB 002fMI-Data-Manipulation
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27.16 GDB/MI Data Manipulation
This section describes the GDB/MI commands that manipulate data: examine memory and registers, evaluate expressions, etc.
For details about what an addressable memory unit is, see addressable memory unit.
The -data-disassemble
Command
Synopsis
-data-disassemble [ -s start-addr -e end-addr ] | [ -a addr ] | [ -f filename -l linenum [ -n lines ] ] -- mode
Where:
- ‘
start-addr
’ is the beginning address (or
$pc
)- ‘
end-addr
’ is the end address
- ‘
addr
’ is an address anywhere within (or the name of) the function to disassemble. If an address is specified, the whole function surrounding that address will be disassembled. If a name is specified, the whole function with that name will be disassembled.
- ‘
filename
’ is the name of the file to disassemble
- ‘
linenum
’ is the line number to disassemble around
- ‘
lines
’ is 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. Ifend-addr
is specified as a non-zero value, andlines
is lower than the number of disassembly lines betweenstart-addr
andend-addr
, onlylines
lines are displayed; iflines
is higher than the number of lines betweenstart-addr
andend-addr
, only the lines up toend-addr
are displayed.- ‘
mode
’ is one of:
- 0 disassembly only
- 1 mixed source and disassembly (deprecated)
- 2 disassembly with raw opcodes
- 3 mixed source and disassembly with raw opcodes (deprecated)
- 4 mixed source and disassembly
- 5 mixed source and disassembly with raw opcodes
Modes 1 and 3 are deprecated. The output is “source centric” which hasn’t proved useful in practice. See Machine Code, for a discussion of the difference between
/m
and/s
output of thedisassemble
command.
Result
The result of the -data-disassemble
command will be a list named
‘asm_insns
’, the contents of this list depend on the mode
used with the -data-disassemble
command.
For modes 0 and 2 the ‘asm_insns
’ list contains tuples with the
following fields:
address
- The address at which this instruction was disassembled.
func-name
- The name of the function this instruction is within.
offset
- The decimal offset in bytes from the start of ‘
func-name
’. inst
- The text disassembly for this ‘
address
’. opcodes
- This field is only present for modes 2, 3 and 5. This contains the raw opcode bytes for the ‘
inst
’ field.
For modes 1, 3, 4 and 5 the ‘asm_insns
’ list contains tuples named
‘src_and_asm_line
’, each of which has the following fields:
line
The line number within ‘
file
’.file
The file name from the compilation unit. This might be an absolute file name or a relative file name depending on the compile command used.
fullname
Absolute file name of ‘
file
’. It is converted to a canonical form using the source file search path (see Specifying Source Directories) and after resolving all the symbolic links.If the source file is not found this field will contain the path as present in the debug information.
line_asm_insn
This is a list of tuples containing the disassembly for ‘
line
’ in ‘file
’. The fields of each tuple are the same as for-data-disassemble
inmode
0 and 2, so ‘address
’, ‘func-name
’, ‘offset
’, ‘inst
’, and optionally ‘opcodes
’.
Note that whatever included in the ‘inst
’ field, is not
manipulated directly by GDB/MI, i.e., it is not possible to
adjust its format.
GDB Command
The corresponding GDB command is ‘disassemble
’.
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="../../../src/gdb/testsuite/gdb.mi/basics.c", fullname="/absolute/path/to/src/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="../../../src/gdb/testsuite/gdb.mi/basics.c", fullname="/absolute/path/to/src/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",disp="keep",bkptno="1",frame={ func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c", line="5",arch="powerpc"} (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 [ --skip-unavailable ] fmt [ ( regno )*]
Display the registers’ contents. The format according to which the
registers’ contents are to be returned is given by fmt
, 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. The --skip-unavailable
option
indicates that only the available registers are to 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
This command is deprecated, use -data-read-memory-bytes
instead.
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 -data-read-memory-bytes
Command
Synopsis
-data-read-memory-bytes [ -o offset ] address count
where:
- ‘
address
’ - An expression specifying the address of the first addressable memory unit to be read. Complex expressions containing embedded white space should be quoted using the C convention.
- ‘
count
’ - The number of addressable memory units to read. This should be an integer literal.
- ‘
offset
’ - The offset relative to
address
at which to start reading. This should be an integer literal. This option is provided so that a frontend is not required to first evaluate address and then perform address arithmetics itself.
This command attempts to read all accessible memory regions in the specified range. First, all regions marked as unreadable in the memory map (if one is defined) will be skipped. See Memory Region Attributes. Second, GDB will attempt to read the remaining regions. For each one, if reading full region results in an errors, GDB will try to read a subset of the region.
In general, every single memory unit in the region may be readable or not, and the only way to read every readable unit is to try a read at every address, which is not practical. Therefore, GDB will attempt to read all accessible memory units at either beginning or the end of the region, using a binary division scheme. This heuristic works well for reading across a memory map boundary. Note that if a region has a readable range that is neither at the beginning or the end, GDB will not read it.
The result record (see GDB/MI Result Records) that is output of
the command includes a field named ‘memory
’ whose content is a
list of tuples. Each tuple represent a successfully read memory block
and has the following fields:
begin
- The start address of the memory block, as hexadecimal literal.
end
- The end address of the memory block, as hexadecimal literal.
offset
- The offset of the memory block, as hexadecimal literal, relative to the start address passed to
-data-read-memory-bytes
. contents
- The contents of the memory block, in hex.
GDB Command
The corresponding GDB command is ‘x
’.
Example
(gdb) -data-read-memory-bytes &a 10 ^done,memory=[{begin="0xbffff154",offset="0x00000000", end="0xbffff15e", contents="01000000020000000300"}] (gdb)
The -data-write-memory-bytes
Command
Synopsis
-data-write-memory-bytes address contents -data-write-memory-bytes address contents [count]
where:
- ‘
address
’ - An expression specifying the address of the first addressable memory unit to be written. Complex expressions containing embedded white space should be quoted using the C convention.
- ‘
contents
’ - The hex-encoded data to write. It is an error if
contents
does not represent an integral number of addressable memory units. - ‘
count
’ - Optional argument indicating the number of addressable memory units to be written. If
count
is greater thancontents
’ length, GDB will repeatedly writecontents
until it fillscount
memory units.
GDB Command
There’s no corresponding GDB command.
Example
(gdb) -data-write-memory-bytes &a "aabbccdd" ^done (gdb)
(gdb) -data-write-memory-bytes &a "aabbccdd" 16e ^done (gdb)
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