From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH v3 01/17] y2038: asm-generic: Extend sysvipc data structures Date: Thu, 19 Apr 2018 23:24:36 +0200 Message-ID: References: <20180419143737.606138-1-arnd@arndb.de> <20180419143737.606138-2-arnd@arndb.de> <87efjbnswr.fsf@xmission.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: "Eric W. Biederman" Cc: y2038 Mailman List , Linux Kernel Mailing List , Linux API , linux-arch , GNU C Library , Thomas Gleixner , Deepa Dinamani , Al Viro , Albert ARIBAUD , linux-s390 , Martin Schwidefsky , the arch/x86 maintainers , Catalin Marinas , Will Deacon , "open list:RALINK MIPS ARCHITECTURE" , James Hogan , Ralf Baechle , linuxppc-dev List-Id: linux-api@vger.kernel.org On Thu, Apr 19, 2018 at 5:20 PM, Arnd Bergmann wrote: > On Thu, Apr 19, 2018 at 4:59 PM, Eric W. Biederman wrote: >> I suspect you want to use __kernel_ulong_t here instead of a raw >> unsigned long. If nothing else it seems inconsistent to use typedefs >> in one half of the structure and no typedefs in the other half. > > Good catch, there is definitely something wrong here, but I think using > __kernel_ulong_t for all members would also be wrong, as that > still changes the layout on x32, which effectively is > > struct msqid64_ds { > ipc64_perm msg_perm; > u64 msg_stime; > u32 __unused1; > /* 32 bit implict padding */ > u64 msg_rtime; > u32 __unused2; > /* 32 bit implict padding */ > u64 msg_ctime; > u32 __unused3; > /* 32 bit implict padding */ > __kernel_pid_t shm_cpid; /* pid of creator */ > __kernel_pid_t shm_lpid; /* pid of last operator */ > .... > }; > > The choices here would be to either use a mix of > __kernel_ulong_t and unsigned long, or taking the x32 > version back into arch/x86/include/uapi/asm/ so the > generic version at least makes some sense. > > I can't use __kernel_time_t for the lower half on 32-bit > since it really should be unsigned. After thinking about it some more, I conclude that the structure is simply incorrect on x32: The __kernel_ulong_t usage was introduced in 2013 in commit b9cd5ca22d67 ("uapi: Use __kernel_ulong_t in struct msqid64_ds") and apparently was correct initially as __BITS_PER_LONG evaluated to 64, but it broke with commit f4b4aae18288 ("x86/headers/uapi: Fix __BITS_PER_LONG value for x32 builds") that changed the value of __BITS_PER_LONG and introduced the extra padding in 2015. The same change apparently also broke a lot of other definitions, e.g. $ echo "#include " | gcc -mx32 -E -xc - | grep -A3 __kernel_size_t typedef unsigned int __kernel_size_t; typedef int __kernel_ssize_t; typedef int __kernel_ptrdiff_t; Those used to be defined as 'unsigned long long' and 'long long' respectively, so now all kernel interfaces using those on x32 became incompatible! Arnd