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    Subject[PATCH 03/11] uml: fix signal code x86-64 [for 2.6.15]
    Date
    From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

    The problems in this area came to light while fixing a compile failure with
    GCC 4, in commit bcb01b8a67476e6f748086e626df8424cc27036d. I went comparing this
    code with x86_64 frame construction (which we should ABI compatible with) and
    resync'ed the code a bit.

    It isn't yet perfect, because we don't yet save floating point context. But that
    will come later.

    Please give a critical eye, even because things currently have no reported
    misbehaviour, and this code is complex enough.

    CC: Andi Kleen <ak@suse.de>
    Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
    ---

    arch/um/sys-x86_64/signal.c | 19 ++++++++++++++++---
    1 files changed, 16 insertions(+), 3 deletions(-)

    diff --git a/arch/um/sys-x86_64/signal.c b/arch/um/sys-x86_64/signal.c
    --- a/arch/um/sys-x86_64/signal.c
    +++ b/arch/um/sys-x86_64/signal.c
    @@ -164,6 +164,7 @@ struct rt_sigframe

    #define round_down(m, n) (((m) / (n)) * (n))

    +/* Taken from arch/x86_64/kernel/signal.c:setup_rt_frame(). */
    int setup_signal_stack_si(unsigned long stack_top, int sig,
    struct k_sigaction *ka, struct pt_regs * regs,
    siginfo_t *info, sigset_t *set)
    @@ -173,9 +174,21 @@ int setup_signal_stack_si(unsigned long
    int err = 0;
    struct task_struct *me = current;

    - frame = (struct rt_sigframe __user *)
    - round_down(stack_top - sizeof(struct rt_sigframe), 16) - 8;
    - frame = (struct rt_sigframe *) ((unsigned long) frame - 128);
    + /* Leave space on the stack for the Red Zone, and for saving FP
    + * registers, even if this doesn't happen. We don't have a way to test
    + * used_math(), so we do that inconditionally.
    + *
    + * XXX: RED-PEN: currently, we're using a Red Zone also for any
    + * alternate stack set up by sigaltstack(), which x86-64 doesn't do
    + * (because there shouldn't be any code executing there). This could
    + * cause failures if user setup a too little alternate stack.*/
    +
    + fp = (struct rt_sigframe *) round_down(stack_top - 128 -
    + sizeof(struct _fpstate), 16);
    +
    + /* Now leave the space for the rest of signal frame. */
    + frame = (void __user *) round_down((unsigned long) fp -
    + sizeof(struct rt_sigframe), 16) - 8;

    if (!access_ok(VERIFY_WRITE, fp, sizeof(struct _fpstate)))
    goto out;
    -
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