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About linux : How-does-the-gettimeofday-syscall-wor‍k

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gettimeofday is a syscall of x86-86 according to this page(just search gettimeofday in the box):

int gettimeofday(struct timeval *tv, struct timezone *tz);

I thought the disassembly should be easy enough, just prepare the two pointers and call the related syscall, but its disassembly is doing much more:

(gdb) disas gettimeofday
Dump of assembler code for function gettimeofday:
0x00000034f408c2d0 <gettimeofday+0>: sub    $0x8,%rsp
0x00000034f408c2d4 <gettimeofday+4>: mov    $0xffffffffff600000,%rax
0x00000034f408c2db <gettimeofday+11>: callq  *%rax
0x00000034f408c2dd <gettimeofday+13>: cmp    $0xfffff001,%eax
0x00000034f408c2e2 <gettimeofday+18>: jae    0x34f408c2e9 <gettimeofday+25>
0x00000034f408c2e4 <gettimeofday+20>: add    $0x8,%rsp
0x00000034f408c2e8 <gettimeofday+24>: retq   
0x00000034f408c2e9 <gettimeofday+25>: mov    0x2c4cb8(%rip),%rcx        # 0x34f4350fa8 <free+3356736>
0x00000034f408c2f0 <gettimeofday+32>: xor    %edx,%edx
0x00000034f408c2f2 <gettimeofday+34>: sub    %rax,%rdx
0x00000034f408c2f5 <gettimeofday+37>: mov    %edx,%fs:(%rcx)
0x00000034f408c2f8 <gettimeofday+40>: or     $0xffffffffffffffff,%rax
0x00000034f408c2fc <gettimeofday+44>: jmp    0x34f408c2e4 <gettimeofday+20>
End of assembler dump. 

And I don’t see syscall at all.

Can anyone explain how it works?

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