pid_t getpid(void);
-------------------

getpid  returns  the  process  ID  of the current process.

x86/Linux

00000000 <getpid>    pushl  %ebp
00000001 <getpid+1>  movl   %esp,%ebp
00000003 <getpid+3>  movl   $0x14,%eax
00000008 <getpid+8>  int    $0x80
0000000a <getpid+a>  testl  %eax,%eax
0000000c <getpid+c>  jnl    0000001a <getpid+1a>
0000000e <getpid+e>  negl   %eax
00000010 <getpid+10> movl   %eax,0x0
00000015 <getpid+15> movl   $0xffffffff,%eax
0000001a <getpid+1a> movl   %ebp,%esp
0000001c <getpid+1c> popl   %ebp


RELOCATION RECORDS FOR [.text]:
OFFSET   TYPE              VALUE 
00000010 R_386_32          errno


Alpha/Digital UNIX

        __getpid:
  0x10: 43e29400        addq    zero, 0x14, v0
  0x14: 00000083        call_pal        callsys
  0x18: e6600005        beq     a3, 0x30
  0x1c: c3a00000        br      gp, 0x20
  0x20: 27bd0001        ldah    gp, 1(gp)
  0x24: 23bd8030        lda     gp, -32720(gp)
  0x28: a79d8010        ldq     at, -32752(gp)
  0x2c: 6bfc0000        jmp     zero, (at), _cerror
  0x30: 6bfa8001        ret     zero, (ra), 1