How To Find The Value In A Register Gdb

This is going to exist a small sit-in or 'tip' to analyze registers and memory via gdb when debugging a program. These commands are pretty much useful when debugging a program. It has its own use cases.

Examine registers:

$info registers is the control which can exist used to come across current register values at the moment from gdb prompt. Below command can be used as a brusque cut to view registers:

(gdb) i r rax 0x1 1 rbx 0x7fff955a9df0 140735699131888 rcx 0xffffffffffffffff -1 rdx 0x7fff955a9e70 140735699132016 rsi 0x7fff955a9df0 140735699131888 rdi 0x16 22 rbp 0x7fff955a9e70 0x7fff955a9e70 rsp 0x7fff955a9dc0 0x7fff955a9dc0 r8 0x7fff955a9dd0 140735699131856 r9 0x1 1 r10 0x7fff955a9ef0 140735699132144 r11 0x293 659 r12 0x7fff955a9ef0 140735699132144 r13 0x0 0 r14 0x1 1 r15 0x0 0 rip 0x37e78da373 0x37e78da373 eflags 0x293 [ CF AF SF IF ] cs 0x33 51 ss 0x2b 43 ds 0x0 0 es 0x0 0 fs 0x0 0 gs 0x0 0

Register information can exist fetched individually . For ex: "Stack pointer" and "Education pointer" information can be fetched past:

                                  
                  (gdb) i r $sp
                  sp: 0x7fff955a9dc0
                  (gdb) i r $rip
                  rip            0x37e78da373    0x37e78da373
                  (gdb)

Examining retention :

This is pretty much useful when debugging a plan:

"x" is the command which can exist used for the same purpose.. The general format of 'x' command every bit shown hither.

                                  
                  (gdb) help x                  Examine retentiveness: x/FMT ADDRESS.                  
                  ADDRESS is an expression for the memory accost to examine.
                    FMT is a repeat count followed past a format letter and a size alphabetic character.
                    Format letters are o(octal), x(hex), d(decimal), u(unsigned decimal),
                    t(binary), f(float), a(address), i(instruction), c(char) and s(string).
                    Size letters are b(byte), h(halfword), w(word), g(giant, 8 bytes).
                    The specified number of objects of the specified size are printed
                    co-ordinate to the format.
                  Defaults for format and size letters are those previously used.
                    The default count is 1.  The default address is the post-obit the last thing printed
                    with this control or "impress".
                    (gdb)
                  In short :
                  Formats:
                    o – octal
                    d – decimal
                    10 – hexadecimal
                    u – unsigned integer
                    s – string
                    t – binary
                  Units:
                    b – byte
                    h – half
                    westward – word
                    thousand – double discussion
                  Instance use of 'x' command:
                  "three" words of memory 'higher up' stack pointer tin be displayed by:                  
                                      Just why I used "above" hither? 'Ans': It is homework/assignment for you 🙂
                  (gdb) x/3xw $sp
                    0x7fff955a9dc0:    0x00000000    0x00000000    0x0041ecb1
                    (gdb)
                  "two" machine instructions from 0x37e78da373/eip
                  (gdb) x/2i 0x37e78da373
                    => 0x37e78da373 :    mov    (%rsp),%rdi
                    0x37e78da377 :    mov    %rax,%rdx
                    (gdb)
                  To display a string yous can apply: ' I selected a random accost', so it may non give a human-readable example string as output.
                  (gdb) x/due south 0x0041ecb1
                    0x41ecb1:     "A\211\307藟\001"
                    (gdb)