[Xen-devel] System Calls in x86_32

[Ahmed Moneeb Azab <amazab@xxxxxxxx>]

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


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