Dobin 0x11_MemoryLayout.pdf

Stack:

• There is one contiguous memory region containing the stack for the process
• LIFO - Last in, First Out
• Contains funtion local variables
• Also contains: Saved Instruction Pointer (SIP)
• Current function adds data to the top (bottom) of the stack

Heap: 

• There is on contiguous memory region containing the heap
• Memory allocator returns specific pieces of the memory region
• For malloc()
• Alos contains: heap management data

Code region contains:

• Compiled program code

Programs are stored in ELF files

ELF: Executable and Linkable Format

• Like COFF, PE (EXE), ....

ELF types:

• ET_EXEC: Executable File
• ET_REL: Relocatable File
• ET_DYN: Shared Object File

ELF "views"

• Sections
• Segments

Sturcture of ELF file from top to bottom:

1. ELF Header
2. Program Header Table (contains the location of sections)
3. Sections (are contained in segments)
4. Section Header Table (contains locationn of sections

Sections:

• .text: Executable instructions
• .bss: Unitialized data (usualy the heap)
• .data: initialized data
• .rodata: Read-Only data
• .got: Global Offset Table
• .plt: Prcedure Linkage Table
• .init / .fini: initialiyation instructions ("glibc")

.plt, .text, .init get written into code block

.got, .data, .bss is written into the heap

unalocated space is the stack.

The process of creating a process from an ELF file is called: "Linking and Loading"

Sections:

• Are for compiler (gcc), to link several objec t files together (.o)

Segments:

• Are for the loader, to create the process
• Consists of one or more sections