Re: [PATCH v4 0/2] Basic nested VMX test suite

[Paolo Bonzini <pbonzini@redhat.com>]

Il 17/07/2013 15:48, Arthur Chunqi Li ha scritto:
> Actually, both structure are kind to me and except for some concerns
> Gleb's solutions seems easier to read.
> 
> The first concern is Gleb's way cannot set a seperate stack for
> HOST_RSP, which I predefined this can be set by test suite's init
> function. I have discussed with Jan and he said we don't have such
> test cases.
> 
> The second is huge function and more assembler codes, I will separate
> vmx_handler codes and this is not important.
> 
> I have another question, I write codes like this:
> 
> asm volatile("vmlaunch;seta %0\n\t" : "=m"(ret));

Note that this asm needs a "memory" clobber too.  This is what I
referred to as "more complications in where to put compiler barriers" in
my earlier message.  In general, bypassing compiler optimizations is why
I preferred your earlier solution.

> /* Should not reach here */
> printf("%s : vmlaunch failed, ret=%d.\n", __func__, ret);
> goto err;
> 
> while(1) {
> ....
> }
> 
> Then because we use -O1 optimization param for our test cases, all the
> codes after "goto" are gone and I got the following error:
> 
> /root/xelatex.kvm-unit-tests-vmx.git/x86/vmx.c:247: undefined
> reference to `vmx_return'
> collect2: ld returned 1 exit status
> 
> So how could I disable the opt for this function or bypass such occasion?

You can do something like

   ret = 0;
   asm volatile("vmlaunch;seta %0\n\t" : "=m"(ret) : : "memory");
   /* Actually we go straight to the while(1) below if ret==0 */
   if (ret) {
       printf("%s : vmlaunch failed, ret=%d.\n", __func__, ret);
       goto err;
   }

   while(1) {
       ...
   }

or if you want to make it more explicit to the compiler:

   ret = 0;
   /* asm goto cannot have outputs :( */
   asm volatile goto ("vmlaunch;seta (%0)\n\t" : : "r"(&ret)
                      : "memory" : resume);
   printf("%s : vmlaunch failed, ret=%d.\n", __func__, ret);
   goto err;

resume:
   while(1) {
       ...
   }

Paolo