Date: Thu, 14 Jun 2018 10:20:45 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: broken __kernel_mode_t affecting some big endian archs On Thu, Jun 14, 2018 at 01:19:31PM +0200, Natanael Copa wrote: > On Wed, 13 Jun 2018 20:54:42 -0400 > Rich Felker <dalias@...c.org> wrote: > > > It's been semi-known for a long time (I say semi-, because nobody's > > had the setup to test most of them well, or at least nobody I'm > > communicating with regularly) that some archs are failing libc-test > > sysvipc tests. I think I've tracked down the root cause. > > > > Linux defined __kernel_mode_t as short on some old archs, and used it > > in place of mode_t in the ipc_perm structure. The field is padded out > > to 32 bits, so on little endian archs it's no problem for us to just > > (as we do) ignore the incorrect type and declare the structure with > > mode_t, as POSIX requires. However on big-endian archs, the padding is > > on the wrong side and this trick doesn't work. > > > > On MIPS we fixed a similar issue in struct stat, where dev_t was > > incorrectly padded, with a fixup in syscall_arch.h. However this time > > a large number of archs are affected, and patching them all up > > individually seems nasty. > > > > My leaning is to have syscall_arch.h expose a macro indicating the > > bug, and have msgctl, semctl, and shmctl each do the fixup if it's > > set. > > > > FWIW the affected archs seem to be (only in big endian variants): > > - ARM > > - M68k (in-progress port) > > - Microblaze > > - SH > > - Sparc (future port) > > Is s390s affected too? Presumably you mean s390x, and it's not affected -- the bad (short) definition of __kernel_mode_t is contingent on 32-bit s390 in the s390 version of asm/posix_types.h. This seems to be a pattern across several archs with 32/64 bit variants, and there doesn't seem to be any explanation for why it should be except possibly that, when adding the 64-bit variant, somebody noticed the awful legacy __kernel_mode_t definition and thought to fix it... Rich
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