From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53272) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cnkh0-00012Z-IF for qemu-devel@nongnu.org; Tue, 14 Mar 2017 07:32:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cnkgx-0000AN-QM for qemu-devel@nongnu.org; Tue, 14 Mar 2017 07:32:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37410) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cnkgx-00009P-Jr for qemu-devel@nongnu.org; Tue, 14 Mar 2017 07:32:39 -0400 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C3AF080461 for ; Tue, 14 Mar 2017 11:32:39 +0000 (UTC) Date: Tue, 14 Mar 2017 11:32:35 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20170314113234.GE2445@work-vm> References: <20170313195547.21466-1-eblake@redhat.com> <20170313195547.21466-7-eblake@redhat.com> <20170313200752.GG5512@work-vm> <89b9b8e6-b5ca-8056-783b-598e07bf5da0@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <89b9b8e6-b5ca-8056-783b-598e07bf5da0@redhat.com> Subject: Re: [Qemu-devel] [PATCH v2 06/30] trace: Fix parameter types in migration List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake Cc: qemu-devel@nongnu.org, stefanha@redhat.com, Juan Quintela * Eric Blake (eblake@redhat.com) wrote: > On 03/13/2017 03:07 PM, Dr. David Alan Gilbert wrote: > > * Eric Blake (eblake@redhat.com) wrote: > >> An upcoming patch will let the compiler warn us when we are silently > >> losing precision in traces; update the trace definitions to pass > >> through the full value at the callsite. > >> > >> Signed-off-by: Eric Blake > >> --- > >> migration/trace-events | 4 ++-- > >> 1 file changed, 2 insertions(+), 2 deletions(-) > >> > > >> -postcopy_ram_fault_thread_request(uint64_t hostaddr, const char *ramblock, size_t offset) "Request for HVA=%" PRIx64 " rb=%s offset=%zx" > >> +postcopy_ram_fault_thread_request(unsigned long long hostaddr, const char *ramblock, size_t offset) "Request for HVA=%llx rb=%s offset=%zx" > > > > Hmm - why? > > That's called as: > > trace_postcopy_ram_fault_thread_request(msg.arg.pagefault.address, > > qemu_ram_get_idstr(rb), > > rb_offset); > > struct uffd_msg msg; > > struct uffd_msg { > > .. > > union { > > struct { > > __u64 flags; > > __u64 address; > > } pagefault; > > .. > > } arg; > > } > > > > So why is a PRIx64 not the right way to print a __u64 ? > > Because __u64 is not the same type as uint64_t. On 64-bit Linux, __u64 > is 'unsigned long long', while uint64_t is 'unsigned long'. > > > (I prefer %llx to the horrid PRIx64 syntax, but it still seems weird in this case) > > As it is, I'm not sure if __u64 is always 'unsigned long long' in ALL > Linux clients; an even-more-conservative patch would be to switch all > callers to use explicit casts to something (like uint64_t or unsigned > long long) that we have full control over, rather than passing __u64 > where we have no control over what type it ultimately resolves to. That would be my preference - casting to (uint64_t) at the caller and keep this as PRIx64. We know it's a 64bit value so we should never use unsigned long long anywhere for it. Dave > > -- > Eric Blake eblake redhat com +1-919-301-3266 > Libvirt virtualization library http://libvirt.org > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK