Segmentation faults commonly occur when programs attempt to access memory regions that they are not allowed to access. This article provides an overview of segmentation faults with practical examples. We will discuss how segmentation faults can occur in x86 assembly as well as C along with some debugging techniques.
See the previous article in the series, How to use the ObjDump tool with x86.
What are segmentation faults in x86 assembly?
A segmentation fault occurs when a program attempts to access a memory location that it is not allowed to access, or attempts to access a memory location in a way that is not allowed (for example, attempting to write to a read-only location).
Let us consider the following x86 assembly example.
message db “Welcome to Segmentation Faults! ”
mov eax, 4
mov ebx, 1
mov ecx, message
mov edx, 32
As we can notice, the preceding program calls the subroutine _printMessage when it is executed. When we read this program without executing, it looks innocent without any evident problems. Let us assemble and link it using the following commands.