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Tue, 8 May 2018 14:12:35 -0400 Received: from mail-pl0-f67.google.com ([209.85.160.67]:37208 "EHLO mail-pl0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933026AbeEHSMd (ORCPT ); Tue, 8 May 2018 14:12:33 -0400 X-Google-Smtp-Source: AB8JxZpn8YotiDjey9gcEcXDLm9f62D9CcjcYDJOZgLS5nvG8cK1CZtaZVEONIj266qKarht4uLaIg== Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 10.3 \(3273\)) Subject: Re: [PATCH] compiler-gcc: disable -ftracer for __noclone functions From: Nadav Amit In-Reply-To: <86f2fb42-b0eb-46d2-0aed-7efdb306bfe0@redhat.com> Date: Tue, 8 May 2018 11:12:30 -0700 Cc: Linux Kernel Mailing List , kvm list , lkml@tlinx.org, Andrew Morton , Michal Marek , stable@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <6E5A36F3-F83E-4022-BE3A-88F1BADA3EEF@gmail.com> References: <1459410252-15531-1-git-send-email-pbonzini@redhat.com> <6BAD64FE-CC59-40C3-9C42-90BB8EEE5453@gmail.com> <86f2fb42-b0eb-46d2-0aed-7efdb306bfe0@redhat.com> To: Paolo Bonzini X-Mailer: Apple Mail (2.3273) Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: Paolo Bonzini wrote: > On 05/05/2018 19:22, Nadav Amit wrote: >> Paolo Bonzini wrote: >>=20 >>> -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 >>> Cc: Michal Marek >>> Cc: stable@vger.kernel.org >>> Cc: kvm@vger.kernel.org >>> Reported-by: Linda Walsh >>> Signed-off-by: Paolo Bonzini >>> --- >>> 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"))) >>=20 >> [ Bringing the thread back from the dead for context ] >>=20 >> 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. >=20 > Hmm, I suppose we need to disable -fno-tracer globally... Has this > changed in recent versions of GCC? I don=E2=80=99t think so. I played with optimization attributes of gcc = some time ago and saw the same behavior. Unfortunately, I don=E2=80=99t easily find = the place in gcc that implements this behavior.