change readonly declared variable to readwrite linux

Change readonly declared variable to readwrite linux code#

It is not necessarily that const global and constant string go in the data section. A constant string does not only go in the data section but all types of const global data go in that section. In the above example, we are not able to change the array character is because it is a literal string. Now see the other example code, #include You can also see that I am able to change the value so it has read and write permission.

You can see the above example str is a global array, so it will go in the data segment. So let us see two C programs to understand this concept. In the data segment, I have said that the “data segment can be further classified into the two-part initialized read-only area and an initialized read-write area”. The size of the data segment increases as per the initialized global and static variables. Static int data2 = 0 //Stored in uninitialized area Int data1 = 0 //Stored in uninitialized area

Now add the global and static initialized variable and check the size.

bss increases as per the uninitialized global and static variables. Return gcc memory-layout.c -o size memory-layout Static int data2 //Stored in uninitialized area

Now add the global and static uninitialized variable and check the size.Now add the global uninitialized variable and check the size.You can see the size of the data segment has been increased. Static int data =10 // Stored in initialized area Now add the initialized static variable and check the size.Static int data // Stored in uninitialized area Now add a static uninitialized variable and check the size.} gcc memory-layout.c -o size memory-layout

Let see few examples to understand the memory layout of the C program. Note: The size command basically lists section sizes as well as total size for the input object file. It is sharable so that only a single copy needs to be in memory for frequently executed programs such as text editors etc.The text segment is a read-only segment that prevents a program from being accidentally modified.The text segment contains a binary of the compiled program.Static int data2 = 3 //Initialized static variable stored in DS Int data1 = 10 //Initialized global variable stored in DS This segment can be further classified into an initialized read-only area and an initialized read-write area.It has read-write permission so the value of the variable of this segment can be changed at run time.

Change readonly declared variable to readwrite linux code#

The size of this segment is determined by the size of the values in the program’s source code and does not change at run time.It contains the explicitly initialized global and static variables.Static int data2 // Uninitialized static variable stored in BSS Int data1 // Uninitialized global variable stored in BSS The program loader allocates memory for the BSS section when it loads the program.All variables in this segment initialized by the zero(0) and pointer with the null pointer.It contains all uninitialized global and static variables.Questions about dynamic memory allocation.It grows and shrinks in the opposite direction of the stack.Ĭhar *pStr = malloc(sizeof(char)*4) //stored in heap.The Heap area is shared by all shared libraries and dynamically loaded modules in a process.Heap area managed by the memory management functions like malloc, calloc, free, etc which may internally use the brk and sbrk system calls to adjust its size.

It is used to allocate the memory at run time.Int data //local variable stored in stack SP(stack pointer) register tracks the top of the stack.Function variables are pushed onto the stack when called and functions variables are popped off the stack when return. Stack frames contain the function’s local variables arguments and return value.A stack frame will create in the stack when a function is called.The stack contains local variables from functions and related book-keeping data.It located at a higher address and grows and shrinks opposite to the heap segment.as dynamic libraries, and different memoryīrk point -> | -| Dynamic memory is declared on the heap The actual static memory layout is specific to the processor, development tools, and the underlying hardware.ĥ. Note: You must remember that this is only an example. Below find the memory Layout of C Program A core file (core dumped file) also associated with a segmentation fault that is used by the developer to finding the root cause of the crashing (segmentation fault). If a program tries to access the memory in a way that is not allowed then segmentation fault occurs.Ī segmentation fault is a common problem that causes programs to crash. Basically, the memory layout of C program contains five segments these are the stack segment, heap segment, BSS (block started by symbol), DS (Data Segment) and text segment.Įach segment has own read, write and executable permission.