glibc and the vsyscall page

[Sharath George]

How does glibc trap into the kernel for x86 systems.
I notice that the kernel has a vsyscall-int80.S file which is made available 
to the userspace.
My question is , by default does glibc direcly use the int $0x80 instruction 
or does it make a call into the vsyscall page provided by the kernel?

Thanks in advance,
Sharath

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