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    SubjectRe: [PATCH] compat: Fix endian issue in union sigval
    On Tue, Feb 24, 2015 at 04:54:17PM -0500, Chris Metcalf wrote:
    > On 2/14/2015 6:22 AM, Catalin Marinas wrote:
    > >1. user populates sival_int compat_sigevent and invokes
    > > compat_sys_mq_notify()
    > >2. kernel get_compat_sigevent() copies compat_sigevent into the native
    > > sigevent. compat and native sival_int are the same, no problem so
    > > far. The other half of 64-bit sival_ptr is zeroed by a memset in this
    > > function (this other half can be top or bottom, depending on
    > > endianness)
    > >3. signal is about to be delivered to user via arch code. The
    > > compat_ptr(from->si_ptr) conversion always takes the least
    > > significant part of the native si_ptr. On big endian 64-bit, this is
    > > zero because get_compat_sigevent() populated the top part of si_ptr
    > > with si_int.
    > >
    > >So delivering such signals to compat user always sets si_int to 0.
    > >Little endian is fine.
    > I looked at this again as I was getting ready to do a tile patch, and realized
    > why tile and arm64 are different here: tile does a field-by-field copy in
    > copy_siginfo_from_user32(), like parisc and s390. As a result, we initialize
    > the 64-bit kernel si_ptr value by cast from the 32-bit user si_ptr value, rather
    > than blindly writing into the lower-addressed half of the 64-bit sigval.

    It's not about copy_siginfo_from_user32() but the generic
    get_compat_sigevent() which always uses sival_int (called from e.g.


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