How to disassemble a memory range with GDB?

Question

I\'m trying to disassemble a program to see a syscall assembly instruction (the INT instruction, I believe) and the handler with GDB and have written a little program (see b

Answer 1

fopen() is a C library function and so you won't see any syscall instructions in your code, just a regular function call. At some point, it does call open(2), but it does that via a trampoline. There is simply a jump to the VDSO page, which is provided by the kernel to every process. The VDSO then provides code to make the system call. On modern processors, the SYSCALL or SYSENTER instructions will be used, but you can also use INT 80h on x86 processors.