[Bug 65561] KVM:Entry failed on Single stepping sti instruction

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=65561

--- Comment #18 from Jidong Xiao <jidong.xiao@gmail.com> ---
Hi, Paolo,

I am still reading the source code so as to understand the root cause of this
problem. In particular, I added some printk statements in x86_emulate_insn().
For example, I added the following printk statement.

...
        switch (c->b) {
        case 0x00 ... 0x05:
                printk(KERN_ERR "DEBUG: Passed %s %d
\n",__FUNCTION__,__LINE__);
              add:              /* add */
                emulate_2op_SrcV("add", c->src, c->dst, ctxt->eflags);
                break;
...

And then in the guest OS, I run a c program like this:

linux:~/code/testc # cat test.c
#include <stdio.h>

int main(void)
{
        int foo = 10, bar = 15;
        __asm__ __volatile__("add  %%ebx,%%eax"
                             :"=a"(foo)
                             :"a"(foo), "b"(bar)
                             );
        printf("foo+bar=%d\n", foo);
        return 0;
}

I thought that because I am using the "add" instruction, the printk statement
in the host os kernel should be invoked, however, my experimental result prove
it's untrue. So I am totally confused with this kvm emulator.

If the kvm trying to emulate these instructions, why that, when I run these
instructions in the guest, the corresponding emulate code are not invoked? So
how to trigger this printk statement? Thanks.

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