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Subject: Re: [PATCH] compiler-gcc: disable -ftracer for __noclone functions
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <1459410252-15531-1-git-send-email-pbonzini@redhat.com>
Date:   Sat, 5 May 2018 10:22:10 -0700
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        kvm list <kvm@vger.kernel.org>, lkml@tlinx.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Marek <mmarek@suse.cz>, stable@vger.kernel.org
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References: <1459410252-15531-1-git-send-email-pbonzini@redhat.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
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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
>=20
>    asm("2: ... \n
>         .pushsection data \n
>         .global vmx_return \n
>         vmx_return: .long 2b");
>=20
> and -ftracer causes a double declaration.
>=20
> 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(-)
>=20
> 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()
>=20
> /* 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 =E2=80=9Coptimizations=
=E2=80=9D. 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=