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    SubjectRe: [PATCH] uprobes/core: handle breakpoint and signal step exception.

    * Srikar Dronamraju <srikar@linux.vnet.ibm.com> wrote:

    > * Ingo Molnar <mingo@elte.hu> [2012-03-08 14:48:09]:
    >
    > >
    > > * Srikar Dronamraju <srikar@linux.vnet.ibm.com> wrote:
    > >
    > > > @@ -233,9 +233,11 @@ static inline void __user *arch_compat_alloc_user_space(long len)
    > > >
    > > > if (test_thread_flag(TIF_IA32)) {
    > > > sp = task_pt_regs(current)->sp;
    > > > +#ifdef CONFIG_X86_64
    > > > } else {
    > > > /* -128 for the x32 ABI redzone */
    > > > sp = __this_cpu_read(old_rsp) - 128;
    > > > +#endif
    > > > }
    > > >
    > > > return (void __user *)round_down(sp - len, 16);
    > >
    > > So 'sp' is undefined if that TIF check fails?
    > >
    > > Also, on a 32-bit kernel the TIF check probably fails all the
    > > time, because we don't set TIF_IA32 (and don't know that flag).
    >
    > >
    > > It would probably be better to make the whole helper inline
    > > #ifdef 64-bit, it does not look very useful on 32-bit.
    > >
    >
    > arch_compat_alloc_user_space gets called from compat_alloc_user_space
    > which is arch agnostic and exported too.
    >
    > So I will change this to
    >
    > void __user *arch_compat_alloc_user_space(long len)
    > {
    > if (is_ia32_compat_task(current))
    > sp = task_pt_regs(current)->sp;
    > #ifdef CONFIG_X86_64
    > else
    > /* -128 for the x32 ABI redzone */
    > sp = __this_cpu_read(old_rsp) - 128;
    > #endif
    >
    > return (void __user *)round_down(sp - len, 16);
    > }
    >
    > where is_ia32_compat_task() is the new macro that you
    > suggested we put in compat.h which would return true if the
    > task is 32 bit emulated on x86_64 or running on i386 machine.
    >
    > Hence we can avoid the case where sp is not set.

    Ok - looks good at first glance.

    Thanks,

    Ingo


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