Memory in GDB (x command)

 

Memory in GDB (x command)

You can use the EXAMINE command (abbreviated as X) to view the value in the memory address. The syntax of the X command is as follows:

X/<n/f/u> <ADDR>

N, f, and u are optional parameters.

N is a positive integer that shows the memory length, that is, the content of several addresses is displayed from the current address to the back.

F indicates the display format. See the preceding figure. If the address refers to a string, the format can be S. If location 10 is the instruction address, the format can be I.
X displays variables in hexadecimal format.
D. Display variables in decimal format.
U displays unsigned integers in hexadecimal format.
O display variables in octal format.
T display variables in binary format.
A displays variables in hexadecimal format.
C. Display variables in character format.
F. Display variables in floating point format.

U indicates the number of bytes requested from the current address. If not specified, GDB defaults to four bytes. The U parameter can be replaced by the following characters. B represents a single byte, H represents a double byte, W represents a four byte, and G represents an octal node. When we specify the byte length, GDB reads and writes the specified byte starting from the memory address specified by the memory and takes it as a value.

Bhwg

X/4bt &

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<ADDR> indicates a memory address.
The n/f/U parameters can be used together. For example:

Command: X/3uh 0x54320 indicates that the content is read from the memory address 0x54320, h indicates that the two bytes are used as a unit, 3 indicates three units, and the u table is displayed in hexadecimal format.

Output Format
Generally, GDB outputs the value of a variable based on the type of the variable. However, you can also customize the output format of GDB. For example, you want to output a hexadecimal integer or a binary value to view the bitwise of the integer variable. To do this, you can use the gdb data display format:

X displays variables in hexadecimal format.
D. Display variables in decimal format.
U displays unsigned integers in hexadecimal format.
O display variables in octal format.
T display variables in binary format.
A displays variables in hexadecimal format.
C. Display variables in character format.
F. Display variables in floating point format.
(GDB) p I
$21 = 101

(GDB) P/A I
$22 = 0x65

(GDB) P/C I
$23 = 101 'E'

(GDB) P/F I
$24 = 1.20.31145e-43

(GDB) P/x I
$25 = 0x65

(GDB) P/T I
$26 = 1100101