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[Xen-devel] System Calls in x86_32

  • To: xen-devel@xxxxxxxxxxxxxxxxxxx
  • From: Ahmed Moneeb Azab <amazab@xxxxxxxx>
  • Date: Tue, 17 Jun 2008 18:56:53 -0400
  • Delivery-date: Tue, 17 Jun 2008 15:57:25 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

Hi All,

I need help understanding how the direct system calls work on the x86_32 architecture.

What I understand is that when a guest is initialized, it uses the hypercall do_set_trap_table to initialize the trap table which calls init_int80_direct_trap for system call interrupts. The later updates the int80_desc structure in the VCPU of the guest so that the new address gets the callback directly.

What I do not understand is where does the call back occur. Int80 is not handles in the x86_32's entry.S?!!!! So, where is the code that issues the callback?

Why is architecture is different on x86_64. The entry.S contains an entry for int80. Does this affect the performance of the guests?


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