I read that in the newer kernels system calls are invoked using the INT X80 instruction and also using the sysenter instruction. And also the sysenter instruction gives faster invocation as compared to the other method.

How could I check which all system calls are invoked by that method?

1 Answer 1


Unless you're running a pre-2.6 kernel, you won't be using the int x80 method for invoking most system calls. They have been replaced in favor of the systenter/sysexit method since kernel 2.6 (started in the 2.5 series) for things that matter.

Note that if you have old binaries that were built against older kernels, those could still be using the int x80 method - the only thing you can do about that is rebuilding them (or getting updated binaries).
Run ldd your_exe on the program you're worried about. If it lists linux-gate.so.1 or linux-vdso.so.1, it's using the new syscalls. If not, it's (most likely) using the old method.
For static binaries, it's harder to tell. One way would be to objdump your_exe | less and look for system call wrappers (__gettimeofday is a good candidate). You'll see from the disassembly if it is using an interrupt or not.

A good rundown of how the old INT 80 calls worked and how the new syscall interface came to be and is setup can be found here: System calls (by Andries Brouwer).
Another good read: What is linux-gate.so.1?.

Both these articles are linked in this other one: Sysenter Based System Call Mechanism in Linux 2.6, and points to the Understanding The Linux Kernel book by Daniel P. Bovet, Marco Cesati which is good for more general information.

So in short: don't worry about it. If you've got a recent-enough system (CPU, kernel and distribution), you're using the "fast" system calls.

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