Operating System-Class 5-Feb. 9^th

C:            int
                long int = long (same C type)

C99:       long long = new type

C doesn’t fix the size in bytes of the numeric types, just requires that

sizeof(long long) >= sizeof(long) >= sizeof(int)
- long long: 64 bits on most current system(that support C99)
- long:  32 bits on (almost) all 32 bit platforms
- int: 32 bits on almost all current platforms, including 64 bit platforms

64 bit Linux(sf06) has:    sizeof(longlong) = 8
                                                sizeof(long) = 8
                                                sizeof(int) = 4

sizeof(void *) = 4 on 32-bit platform / 8 on 64-bit platform

DLL: can be loaded anywhere in address space

- the actual location isn’t known until runtime

o actual location of DLL: saved in memory variable.

o Then to call a function in the DLL, the actual address is loaded and the code does “jump %g1”(jump to loaded address)

UNIX (including Linux) syscalls

- read, write, open, close

- exit

- int fork(): creates a process which is a clone of this process

o return 0 for the child (childpid for parent)

- exec*

o create a new virtual address space for given executable file

o redoes the current VA space

eg. Shell forks a new process, then use exec* syscall to run the command program in the new process.

- sounds wasteful, but memory management can avoid the memory copy

All syscalls: see Section 2 of man pages(syscall manual)

syscalls show all OS capability for a program, vary from UNIX to Windows.

- using syscalls directly in app program means no portability

- what to do?        standard C library – Section 3 of man pages

system to run a command, eg. system(“date”) <-- run in its own process

Java itself has a virtual machine!

XINU syscall:

- int write

- int read

- int putc

- int getc

- int create(caddr, ssize, prio, name, nargs, args, …)

o caddr: start address

o ssize: stack size(create near-empty stacks, just the args)

o prio: priority

o nargs, args: args to pass to new process

o somewhat like Windows CreateProcess

- kill(pid)

o pid: can be own pid

o UNIX: use exit to kill self