Do system calls in x86_64 linux still generate interrupts?

Solution 1:

Yes, modern C code for Linux x86_64 uses the syscall instruction, see for example glibc sysdeps/unix/sysv/linux/x86_64/syscall.S. No, this does not mean system call interrupts go away, due to compatibility.

https://www.kernel.org/doc/Documentation/x86/entry_64.txt

The x86 architecture has quite a few different ways to jump into kernel code. Most of these entry points are registered in arch/x86/kernel/traps.c and implemented in arch/x86/entry/entry_64.S for 64-bit, arch/x86/entry/entry_32.S for 32-bit and finally arch/x86/entry/entry_64_compat.S which implements the 32-bit compatibility syscall entry points and thus provides for 32-bit processes the ability to execute syscalls when running on 64-bit kernels.

The IDT vector assignments are listed in arch/x86/include/asm/irq_vectors.h.

Some of these entries are:

• system_call: syscall instruction from 64-bit code.

• entry_INT80_compat: int 0x80 from 32-bit or 64-bit code; compat syscall either way.

• entry_INT80_compat, ia32_sysenter: syscall and sysenter from 32-bit code

And for read only syscalls (gettimeofday) there is vDSO which does not enter kernel mode at all.

system calls can be profiled in a few ways, such as ftrace or eBPF. In addition to being obsolete in 64 bit mode, interrupts happen for reasons other than system calls.