From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49081) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gWKkz-0007CR-U9 for qemu-devel@nongnu.org; Mon, 10 Dec 2018 07:33:54 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gWKkw-0001Or-Im for qemu-devel@nongnu.org; Mon, 10 Dec 2018 07:33:53 -0500 Received: from mail-wr1-f66.google.com ([209.85.221.66]:34262) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1gWKkw-0001OM-BC for qemu-devel@nongnu.org; Mon, 10 Dec 2018 07:33:50 -0500 Received: by mail-wr1-f66.google.com with SMTP id j2so10323480wrw.1 for ; Mon, 10 Dec 2018 04:33:50 -0800 (PST) References: <20181210114654.31433-1-peter.maydell@linaro.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Mon, 10 Dec 2018 13:33:45 +0100 MIME-Version: 1.0 In-Reply-To: <20181210114654.31433-1-peter.maydell@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH] target/i386/kvm.c: Don't mark cpuid_data as QEMU_PACKED List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell , qemu-devel@nongnu.org Cc: Eduardo Habkost , kvm@vger.kernel.org, patches@linaro.org, Marcelo Tosatti , Paolo Bonzini , Richard Henderson On 12/10/18 12:46 PM, Peter Maydell wrote: > clang complains about taking the address of a packed > member of a struct: > > target/i386/kvm.c:1245:27: warning: taking address of packed member 'cpuid' of class or structure '' may result in an unaligned pointer value [-Waddress-of-packed-member] > c = cpuid_find_entry(&cpuid_data.cpuid, 1, 0); > ^~~~~~~~~~~~~~~~ > target/i386/kvm.c:1297:31: warning: taking address of packed member 'cpuid' of class or structure '' may result in an unaligned pointer value [-Waddress-of-packed-member] > c = cpuid_find_entry(&cpuid_data.cpuid, kvm_base, 0); > ^~~~~~~~~~~~~~~~ > > The kernel's definitions of struct kvm_cpuid2 and struct > kvm_cpuid_entry2 are carefully set up with padding fields > so that there is no between-struct padding anyway, so > the QEMU_PACKED annotation is unnecessary and might result > in the compiler generating worse code. Drop it, and instead > assert at build time that there is no stray padding. > > Signed-off-by: Peter Maydell Reviewed-by: Philippe Mathieu-Daudé > --- > target/i386/kvm.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/target/i386/kvm.c b/target/i386/kvm.c > index b2401d13ea7..739cf8c8ea1 100644 > --- a/target/i386/kvm.c > +++ b/target/i386/kvm.c > @@ -864,7 +864,15 @@ int kvm_arch_init_vcpu(CPUState *cs) > struct { > struct kvm_cpuid2 cpuid; > struct kvm_cpuid_entry2 entries[KVM_MAX_CPUID_ENTRIES]; > - } QEMU_PACKED cpuid_data; > + } cpuid_data; > + /* > + * The kernel defines these structs with padding fields so there > + * should be no extra padding in our cpuid_data struct. > + */ > + QEMU_BUILD_BUG_ON(sizeof(cpuid_data) != > + sizeof(struct kvm_cpuid2) + > + sizeof(struct kvm_cpuid_entry2) * KVM_MAX_CPUID_ENTRIES); > + > X86CPU *cpu = X86_CPU(cs); > CPUX86State *env = &cpu->env; > uint32_t limit, i, j, cpuid_i; >