_syscall1() dump:
Dump of assembler code for function umask:
0x0000000000000030 <umask+0>:   mov    $0x5f,%eax
0x0000000000000035 <umask+5>:   movslq %edi,%rdi
0x0000000000000038 <umask+8>:   syscall
0x000000000000003a <umask+10>:  cmp    $0xffffffffffffff80,%rax
0x000000000000003e <umask+14>:  jbe    0x51 <umask+33>
0x0000000000000040 <umask+16>:  neg    %rax
0x0000000000000043 <umask+19>:  mov    %rax,0(%rip)        # 0x4a <umask+26>
0x000000000000004a <umask+26>:  mov    $0xffffffffffffffff,%rax
0x0000000000000051 <umask+33>:  retq
0x0000000000000052 <umask+34>:  data16
0x0000000000000053 <umask+35>:  data16
0x0000000000000054 <umask+36>:  data16
0x0000000000000055 <umask+37>:  nop
0x0000000000000056 <umask+38>:  data16
0x0000000000000057 <umask+39>:  data16
0x0000000000000058 <umask+40>:  data16
0x0000000000000059 <umask+41>:  nop
0x000000000000005a <umask+42>:  data16
0x000000000000005b <umask+43>:  data16
0x000000000000005c <umask+44>:  nop
0x000000000000005d <umask+45>:  data16
0x000000000000005e <umask+46>:  data16
0x000000000000005f <umask+47>:  nop

INLINE_SYCALL() dump:
Dump of assembler code for function wrapper_umask:
0x0000000000000000 <wrapper_umask+0>:   mov    %edi,%edi
0x0000000000000002 <wrapper_umask+2>:   mov    $0x5f,%rax
0x0000000000000009 <wrapper_umask+9>:   syscall
0x000000000000000b <wrapper_umask+11>:  cmp    $0xfffffffffffff000,%rax
0x0000000000000011 <wrapper_umask+17>:  jbe    0x24 <wrapper_umask+36>
0x0000000000000013 <wrapper_umask+19>:  neg    %rax
0x0000000000000016 <wrapper_umask+22>:  mov    %rax,0(%rip)        # 0x1d <wrapper_umask+29>
0x000000000000001d <wrapper_umask+29>:  mov    $0xffffffffffffffff,%rax
0x0000000000000024 <wrapper_umask+36>:  retq
0x0000000000000025 <wrapper_umask+37>:  data16
0x0000000000000026 <wrapper_umask+38>:  data16
0x0000000000000027 <wrapper_umask+39>:  data16
0x0000000000000028 <wrapper_umask+40>:  nop
0x0000000000000029 <wrapper_umask+41>:  data16
0x000000000000002a <wrapper_umask+42>:  data16
0x000000000000002b <wrapper_umask+43>:  data16
0x000000000000002c <wrapper_umask+44>:  nop
0x000000000000002d <wrapper_umask+45>:  data16
0x000000000000002e <wrapper_umask+46>:  data16
0x000000000000002f <wrapper_umask+47>:  nop


Disassemble of umask() from a statically linked prog:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main()
{
        umask(666);
        return 0;
}


Dump of assembler code for function umask:
0x0000000000406a20 <umask+0>:   mov    $0x5f,%rax
0x0000000000406a27 <umask+7>:   syscall
0x0000000000406a29 <umask+9>:   retq
0x0000000000406a2a <umask+10>:  nop
0x0000000000406a2b <umask+11>:  nop
0x0000000000406a2c <umask+12>:  nop
0x0000000000406a2d <umask+13>:  nop
0x0000000000406a2e <umask+14>:  nop
0x0000000000406a2f <umask+15>:  nop