int read(int fd, char *buf, size_t count);
------------------------------------------

On error, -1 is returned, and errno is set appropriately 
(to a positive number).

x86/Linux

00000000 <read>    pushl  %ebp
00000001 <read+1>  movl   %esp,%ebp
00000003 <read+3>  pushl  %ebx
00000004 <read+4>  movl   $0x3,%eax
00000009 <read+9>  movl   0x8(%ebp),%ebx
0000000c <read+c>  movl   0xc(%ebp),%ecx
0000000f <read+f>  movl   0x10(%ebp),%edx
00000012 <read+12> int    $0x80
00000014 <read+14> testl  %eax,%eax
00000016 <read+16> jnl    00000024 <read+24>
00000018 <read+18> negl   %eax
0000001a <read+1a> movl   %eax,0x0
0000001f <read+1f> movl   $0xffffffff,%eax
00000024 <read+24> popl   %ebx
00000025 <read+25> movl   %ebp,%esp
00000027 <read+27> popl   %ebp

RELOCATION RECORDS FOR [.text]:
OFFSET   TYPE              VALUE 
0000001b R_386_32          errno


Alpha/Digital UNIX

        __read:
  0x10: 43e07400        addq    zero, 0x3, 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