Xen devel - Dec 2008 - GET_CURRENT macro in entry.S

I am unable to understand what this macro in  entry.S does. Can someone
please explain its working?

#define GET_CURRENT(reg)         \
        movl $STACK_SIZE-4, reg; \
        orl  %esp, reg;          \
        andl $~3,reg;            \
        movl (reg),reg;

Also, how does the address of "struct vcpu" come in %ebx ? How do I
obtain
it?

Please help.

-Pallavi


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Bottom of stack is cpu_info structure:

struct cpu_info {
    struct cpu_user_regs guest_cpu_user_regs;
    unsigned int         processor_id;
    struct vcpu         *current_vcpu;
};

Below code locates cpu_info on current stack (esp), and then fetch current_vcpu
pointer into ebx.

Thanks,
Kevin

________________________________
From: xen-devel-bounces@lists.xensource.com
[mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of pallavi jk
Sent: Tuesday, December 30, 2008 12:45 AM
To: xen-devel@lists.xensource.com; Keir Fraser; Jeremy Fitzhardinge
Subject: [Xen-devel] GET_CURRENT macro in entry.S

I am unable to understand what this macro in  entry.S does. Can someone please
explain its working?

#define GET_CURRENT(reg)         \
        movl $STACK_SIZE-4, reg; \
        orl  %esp, reg;          \
        andl $~3,reg;            \
        movl (reg),reg;

Also, how does the address of "struct vcpu" come in %ebx ? How do I
obtain it?

Please help.

-Pallavi


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel