debugging,assembly,x86,gdb , Why is “info register ebp” in gdb not displaying a decimal number?


Why is “info register ebp” in gdb not displaying a decimal number?

Question:

Tag: debugging,assembly,x86,gdb

I am debugging a very simple code with gdb:

mov ebp,eax     ; Save # of bytes read from file for later

Here is my output:

Breakpoint 2, Read () at hexdump1.asm:44
(gdb) info register eax
eax   0xd      13
(gdb) step
Read () at hexdump1.asm:45
(gdb) info register ebp
ebp   0xd      0xd

Why is gdb showing me 0xd 13 for eax but 0xd 0xd for ebp?


Answer:

Your question is why (gdb) info register eax displays the content of EAX with a hex and a decimal number, while (gdb) info register ebx only uses hex numbers for EBP, right?

That is not only the case for EBP, but also for ESP, EFLAGS and EIP, too. I think, that has no special meaning. gdb just tries to display it in a usefull way. For example for EFLAGS, you want to see the status of the flags and not a decimal number (in the example below IF is set). In the case of EBP and ESP, we are talking about registers which are usually used to point to an address in the stack/memory. Thus normally, you do not want to know the decimal value. Okay, in this case, showing hex twice is quite useless though.

Here is an example which displays the content of all registers with the info registers command (i r is the short form, I just found out :P).

    (gdb) i r
    eax            0x0  0
    ecx            0x0  0
    edx            0x0  0
    ebx            0x0  0
    esp            0xbffff234   0xbffff234
    ebp            0x0  0x0
    esi            0x0  0
    edi            0x0  0
    eip            0x804822d    0x804822d 
    eflags         0x202    [ IF ]
    cs             0x73 115
    ss             0x7b 123
    ds             0x7b 123
    es             0x7b 123
    fs             0x0  0
    gs             0x0  0

more infos: https://sourceware.org/gdb/onlinedocs/gdb/Registers.html


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