Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> On 05/05/2018 19:22, Nadav Amit wrote:
>> Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>>
>>> -ftracer can duplicate asm blocks causing compilation to fail in
>>> noclone functions. For example, KVM declares a global variable
>>> in an asm like
>>>
>>> asm("2: ... \n
>>> .pushsection data \n
>>> .global vmx_return \n
>>> vmx_return: .long 2b");
>>>
>>> and -ftracer causes a double declaration.
>>>
>>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>>> Cc: Michal Marek <mmarek@xxxxxxx>
>>> Cc: stable@xxxxxxxxxxxxxxx
>>> Cc: kvm@xxxxxxxxxxxxxxx
>>> Reported-by: Linda Walsh <lkml@xxxxxxxxx>
>>> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>>> ---
>>> include/linux/compiler-gcc.h | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
>>> index 22ab246feed3..eeae401a2412 100644
>>> --- a/include/linux/compiler-gcc.h
>>> +++ b/include/linux/compiler-gcc.h
>>> @@ -199,7 +199,7 @@
>>> #define unreachable() __builtin_unreachable()
>>>
>>> /* Mark a function definition as prohibited from being cloned. */
>>> -#define __noclone __attribute__((__noclone__))
>>> +#define __noclone __attribute__((__noclone__, __optimize__("no-tracer")))
>>
>> [ Bringing the thread back from the dead for context ]
>>
>> Setting different optimization attributes to certain functions apparently
>> prevents gcc from inlining functions with different “optimizations”. This
>> results in poor compilation - most notably of vmx_vcpu_run() - and causes
>> short functions such as to_vmx() not to be inlined.
>
> Hmm, I suppose we need to disable -fno-tracer globally... Has this
> changed in recent versions of GCC?
I don’t think so. I played with optimization attributes of gcc some time ago
and saw the same behavior. Unfortunately, I don’t easily find the place in
gcc that implements this behavior.
