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    Subject[Patch 3/10] Modifying generic debug exception to use virtual debug registers
    This patch modifies the breakpoint exception handler code to use the abstract
    register names.

    Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
    Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
    ---
    arch/x86/kernel/traps.c | 66 +++++++++++++++++-------------------------------
    1 file changed, 24 insertions(+), 42 deletions(-)

    Index: linux-hbkpt-lkml-29-rc2/arch/x86/kernel/traps.c
    ===================================================================
    --- linux-hbkpt-lkml-29-rc2.orig/arch/x86/kernel/traps.c
    +++ linux-hbkpt-lkml-29-rc2/arch/x86/kernel/traps.c
    @@ -570,10 +570,11 @@ asmlinkage __kprobes struct pt_regs *syn
    dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
    {
    struct task_struct *tsk = current;
    - unsigned long condition;
    + unsigned long dr6;
    int si_code;

    - get_debugreg(condition, 6);
    + get_debugreg(dr6, 6);
    + set_debugreg(0, 6); /* DR6 may or may not be cleared by the CPU */

    /*
    * The processor cleared BTF, so don't mark that we need it set.
    @@ -581,61 +582,42 @@ dotraplinkage void __kprobes do_debug(st
    clear_tsk_thread_flag(tsk, TIF_DEBUGCTLMSR);
    tsk->thread.debugctlmsr = 0;

    - if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
    + /* Store the virtualized DR6 value */
    + tsk->thread.vdr6 = dr6;
    +
    + if (notify_die(DIE_DEBUG, "debug", regs, dr6, error_code,
    SIGTRAP) == NOTIFY_STOP)
    return;

    /* It's safe to allow irq's after DR6 has been saved */
    preempt_conditional_sti(regs);

    - /* Mask out spurious debug traps due to lazy DR7 setting */
    - if (condition & (DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)) {
    - if (!tsk->thread.debugreg7)
    - goto clear_dr7;
    + if (regs->flags & X86_VM_MASK) {
    + handle_vm86_trap((struct kernel_vm86_regs *) regs,
    + error_code, 1);
    + return;
    }

    #ifdef CONFIG_X86_32
    - if (regs->flags & X86_VM_MASK)
    - goto debug_vm86;
    #endif

    - /* Save debug status register where ptrace can see it */
    - tsk->thread.debugreg6 = condition;
    -
    - /*
    - * Single-stepping through TF: make sure we ignore any events in
    - * kernel space (but re-enable TF when returning to user mode).
    - */
    - if (condition & DR_STEP) {
    - if (!user_mode(regs))
    - goto clear_TF_reenable;
    - }
    -
    - si_code = get_si_code(condition);
    - /* Ok, finally something we can handle */
    - send_sigtrap(tsk, regs, error_code, si_code);
    -
    /*
    - * Disable additional traps. They'll be re-enabled when
    - * the signal is delivered.
    + * Single-stepping through system calls: ignore any exceptions in
    + * kernel space, but re-enable TF when returning to user mode.
    + *
    + * We already checked v86 mode above, so we can check for kernel mode
    + * by just checking the CPL of CS.
    */
    -clear_dr7:
    - set_debugreg(0, 7);
    - preempt_conditional_cli(regs);
    - return;
    -
    -#ifdef CONFIG_X86_32
    -debug_vm86:
    - handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code, 1);
    - preempt_conditional_cli(regs);
    - return;
    -#endif
    + if ((dr6 & DR_STEP) && !user_mode(regs)) {
    + tsk->thread.vdr6 &= ~DR_STEP;
    + set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
    + regs->flags &= ~X86_EFLAGS_TF;
    + }
    + si_code = get_si_code(dr6);
    + if (tsk->thread.vdr6 & (DR_STEP|DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3))
    + send_sigtrap(tsk, regs, error_code, si_code);

    -clear_TF_reenable:
    - set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
    - regs->flags &= ~X86_EFLAGS_TF;
    preempt_conditional_cli(regs);
    - return;
    }

    #ifdef CONFIG_X86_64

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