[PATCH] compiler-gcc: disable -ftracer for __noclone functions

[PATCH] compiler-gcc: disable -ftracer for __noclone functions

[Paolo Bonzini]

-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@linux-foundation.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: stable@vger.kernel.org
Cc: kvm@vger.kernel.org
Reported-by: Linda Walsh <lkml@tlinx.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 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")))
 
 #endif /* GCC_VERSION >= 40500 */
 
-- 
2.5.5

Re: [PATCH] compiler-gcc: disable -ftracer for __noclone functions

[kbuild test robot]

Hi Paolo,

[auto build test WARNING on v4.6-rc1]
[also build test WARNING on next-20160331]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]

url:    https://github.com/0day-ci/linux/commits/Paolo-Bonzini/compiler-gcc-disable-ftracer-for-__noclone-functions/20160331-154556
reproduce:
        # apt-get install sparse
        make ARCH=x86_64 allmodconfig
        make C=1 CF=-D__CHECK_ENDIAN__


sparse warnings: (new ones prefixed by >>)

   include/linux/compiler.h:232:8: sparse: attribute 'no_sanitize_address': unknown attribute
>> arch/x86/kvm/vmx.c:8610:13: sparse: attribute '__optimize__': unknown attribute

vim +/__optimize__ +8610 arch/x86/kvm/vmx.c

d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8594  	int i, nr_msrs;
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8595  	struct perf_guest_switch_msr *msrs;
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8596  
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8597  	msrs = perf_guest_get_msrs(&nr_msrs);
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8598  
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8599  	if (!msrs)
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8600  		return;
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8601  
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8602  	for (i = 0; i < nr_msrs; i++)
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8603  		if (msrs[i].host == msrs[i].guest)
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8604  			clear_atomic_switch_msr(vmx, msrs[i].msr);
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8605  		else
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8606  			add_atomic_switch_msr(vmx, msrs[i].msr, msrs[i].guest,
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8607  					msrs[i].host);
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8608  }
d7cd9796 arch/x86/kvm/vmx.c Gleb Natapov    2011-10-05  8609  
a3b5ba49 arch/x86/kvm/vmx.c Lai Jiangshan   2011-02-11 @8610  static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
6aa8b732 drivers/kvm/vmx.c  Avi Kivity      2006-12-10  8611  {
a2fa3e9f drivers/kvm/vmx.c  Gregory Haskins 2007-07-27  8612  	struct vcpu_vmx *vmx = to_vmx(vcpu);
d974baa3 arch/x86/kvm/vmx.c Andy Lutomirski 2014-10-08  8613  	unsigned long debugctlmsr, cr4;
104f226b arch/x86/kvm/vmx.c Avi Kivity      2010-11-18  8614  
104f226b arch/x86/kvm/vmx.c Avi Kivity      2010-11-18  8615  	/* Record the guest's net vcpu time for enforced NMI injections. */
104f226b arch/x86/kvm/vmx.c Avi Kivity      2010-11-18  8616  	if (unlikely(!cpu_has_virtual_nmis() && vmx->soft_vnmi_blocked))
104f226b arch/x86/kvm/vmx.c Avi Kivity      2010-11-18  8617  		vmx->entry_time = ktime_get();
104f226b arch/x86/kvm/vmx.c Avi Kivity      2010-11-18  8618  

:::::: The code at line 8610 was first introduced by commit
:::::: a3b5ba49a8c58d9a578e016523b047467a41e047 KVM: VMX: add the __noclone attribute to vmx_vcpu_run

:::::: TO: Lai Jiangshan <laijs@cn.fujitsu.com>
:::::: CC: Marcelo Tosatti <mtosatti@redhat.com>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

Re: [PATCH] compiler-gcc: disable -ftracer for __noclone functions

[Nadav Amit]

Paolo Bonzini <pbonzini@redhat.com> 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@linux-foundation.org>
> Cc: Michal Marek <mmarek@suse.cz>
> Cc: stable@vger.kernel.org
> Cc: kvm@vger.kernel.org
> Reported-by: Linda Walsh <lkml@tlinx.org>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> 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.

Regards,
Nadav

Re: [PATCH] compiler-gcc: disable -ftracer for __noclone functions

[Paolo Bonzini]

On 05/05/2018 19:22, Nadav Amit wrote:
> Paolo Bonzini <pbonzini@redhat.com> 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@linux-foundation.org>
>> Cc: Michal Marek <mmarek@suse.cz>
>> Cc: stable@vger.kernel.org
>> Cc: kvm@vger.kernel.org
>> Reported-by: Linda Walsh <lkml@tlinx.org>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>> 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?

Paolo

Re: [PATCH] compiler-gcc: disable -ftracer for __noclone functions

[Nadav Amit]

Paolo Bonzini <pbonzini@redhat.com> wrote:

> On 05/05/2018 19:22, Nadav Amit wrote:
>> Paolo Bonzini <pbonzini@redhat.com> 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@linux-foundation.org>
>>> Cc: Michal Marek <mmarek@suse.cz>
>>> Cc: stable@vger.kernel.org
>>> Cc: kvm@vger.kernel.org
>>> Reported-by: Linda Walsh <lkml@tlinx.org>
>>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>>> ---
>>> 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.