From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ahmed Moneeb Azab Subject: System Calls in x86_32 Date: Tue, 17 Jun 2008 18:56:53 -0400 Message-ID: <48584135.9000301@ncsu.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org 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? Ahmed