Csapp: Exception Control Flow

In general cases, the sequence of instructions processed by the processor is contiguous (sequential execution).

The exception control flow provides a jump to instructions, part of which is implemented by the hardware, and partly by the operating system.

Exception handling

at system startup, the operating system allocates and initializes a jump table called the exception table:

The code that will find and execute the corresponding exception handler from the Jump table when the exception is triggered (so-called kernel-state code?):

System calls

Each system call is an exception, and an exception is triggered when a system call function in the C library is called.

In a IA32 system, a system call is provided through a trap instruction called an int 0x80 (exception number).

All Linux system calls are passed through registers.

Here is an example of a system call

int Main () {    write (1"Hello, world\n");    Exit (0);      }

The corresponding assembly code

Main:    movl $4,%eax       system call number    MOVL $,%ebx       file descriptor    movl $string,%ecx "Hello, world\n"     movl $len,%edx     length    int $0x80      ...

Csapp: Exception Control Flow