System Calls in deep

What will you learn from this course?

• Basics of Inline Assembly

• Types of Inline Assembly: Basic and Extended

• GCC Assembly Syntax: AT&T

• Constraint strings

• Input and output operands

• Clobbering

• Various use cases of Inline assembly in Linux kernel: Interrupts, I/O Ports, Atomic operations, CPUID, Control Registers, Timestamp counters etc

• Deep understanding of system calls: Various ways of switching from user space to kernel space (int $0x80, sysenter/sysexit, syscall/sysret)

• VDSO

• Adding a new system call which doesn't accept any arguments

• Adding a system call which accept argument

• Kernel Symbols and Kernel Symbol table

• Writing a kernel module which overwrite the kernel symbol table

• Writing a kernel module which sniffs the parameters passed to a system call

Examples covered in this course:

• Add two numbers in inline assembly

• Add three numbers in inline assembly

• Subtract, divide, multiply in inline assembly

• Can we disable/enable interrupts in user space

• Checking whether interrupts are enabled and disabled in user space

• Enabling/Disabling interrupts in user space

• Implementing simple locking to avoid race conditions: Lock prefix, compare and exchange instructions

• And many