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    SubjectRe: [PATCH v2] parisc: fix personality flag check in copy_thread()
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    On Thu, 2012-08-02 at 09:12 +0200, Jiri Kosina wrote:
    > Directly comparing task_struct->personality against PER_* is not fully
    > correct, as it doesn't take flags potentially stored in top three bytes
    > into account.
    >
    > Analogically, directly forcefully setting personality to PER_LINUX32 or
    > PER_LINUX discards any flags stored in the top three bytes.
    >
    > Signed-off-by: Jiri Kosina <jkosina@suse.cz>
    > ---
    >
    > changed since v1: fix the bit ops to reflect the fact that PER_LINUX is
    > actually 0

    Tell me what you're trying to achieve (or what problem you're trying to
    solve), because personality is notoriously tricky.

    Usually personality = <whatever> is desired because if you look at the
    enum for personality, it does set the top three bits in quite a few
    cases. We actually don't need any of the top 3 byte features ... but I
    think making sure they're zeroed out is the correct thing to do.

    In particular, if we ever get around to a 64 bit user space, our
    personality will be PER_LINUX_FDPIC and then we will be setting the top
    three bytes.

    James


    > arch/parisc/kernel/process.c | 2 +-
    > arch/parisc/kernel/sys_parisc.c | 8 ++++----
    > 2 files changed, 5 insertions(+), 5 deletions(-)
    >
    > diff --git a/arch/parisc/kernel/process.c b/arch/parisc/kernel/process.c
    > index d4b94b3..2c05a92 100644
    > --- a/arch/parisc/kernel/process.c
    > +++ b/arch/parisc/kernel/process.c
    > @@ -309,7 +309,7 @@ copy_thread(unsigned long clone_flags, unsigned long usp,
    > cregs->ksp = (unsigned long)stack
    > + (pregs->gr[21] & (THREAD_SIZE - 1));
    > cregs->gr[30] = usp;
    > - if (p->personality == PER_HPUX) {
    > + if (personality(p->personality) == PER_HPUX) {
    > #ifdef CONFIG_HPUX
    > cregs->kpc = (unsigned long) &hpux_child_return;
    > #else
    > diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_parisc.c
    > index c9b9322..7f9658e 100644
    > --- a/arch/parisc/kernel/sys_parisc.c
    > +++ b/arch/parisc/kernel/sys_parisc.c
    > @@ -225,12 +225,12 @@ long parisc_personality(unsigned long personality)
    > long err;
    >
    > if (personality(current->personality) == PER_LINUX32
    > - && personality == PER_LINUX)
    > - personality = PER_LINUX32;
    > + && personality(personality) == PER_LINUX)
    > + personality |= PER_LINUX32;
    >
    > err = sys_personality(personality);
    > - if (err == PER_LINUX32)
    > - err = PER_LINUX;
    > + if (personality(err) == PER_LINUX32)
    > + err &= ~PER_LINUX32;
    >
    > return err;
    > }
    >




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