DIIS

DevHeads IoT Integration Server•17mo ago•

1 reply

Marvee Amasi

Unexpected Memory Value Fluctuations in GDB While Debugging Pointer in x86-64 C Program

In my last question, I misunderstood how GDB interprets memory when using different formats like

x/d

x/d

and

x/1wd

x/1wd

. After some digging, I realized the issue was related to GDB displaying the same memory contents as both signed and unsigned integers. That cleared up the confusion about the "flipping" values.

Funny how I am facing a different issue with pointer manipulation and register inspection. I’m debugging a simple

C

C

program where

$rbx

$rbx

is pointing to dynamically allocated memory. Here's the setup in my main.c file
When I inspect

$rbx

$rbx

in GDB, I expect it to point to the buffer and show the correct values as

28

28

and

-5604

-5604

for

ptr[0]

ptr[0]

and

ptr[1]

ptr[1]

. When I execute these commands, I get some strange behavior which I logged in bash.txt
. Been making use of

x86-64

x86-64

,

GDB version 10.1

GDB version 10.1

and

Ubuntu 20.04

Ubuntu 20.04

as my environment
.
The values at the memory location are flipping between 28 and -5604, even though the program hasn’t modified the memory or stepped through any new instructions. I’m not sure if this is like caching, memory alignment issues, or a problem with the heap?