hw-breakpoints: modifying generic debug exception to use thread-specific debug registers

This patch modifies the breakpoint exception handler code to use the new
abstract debug register names.

[ fweisbec@gmail.com: fix conflict against kmemcheck ]

[ Impact: refactor and cleanup x86 debug exception handler ]

Original-patch-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index a1d2883..de99132 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -529,73 +529,52 @@ asmlinkage __kprobes struct pt_regs *sync_regs(struct pt_regs *eregs)
 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);
 
+       /* DR6 may or may not be cleared by the CPU */
+       set_debugreg(0, 6);
        /*
         * The processor cleared BTF, so don't mark that we need it set.
         */
        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.debugreg6 = 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).
+        * 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.
         */
-       if (condition & DR_STEP) {
-               if (!user_mode(regs))
-                       goto clear_TF_reenable;
+       if ((dr6 & DR_STEP) && !user_mode(regs)) {
+               tsk->thread.debugreg6 &= ~DR_STEP;
+               set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
+               regs->flags &= ~X86_EFLAGS_TF;
        }
-
-       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.
-        */
-clear_dr7:
-       set_debugreg(0, 7);
+       si_code = get_si_code(tsk->thread.debugreg6);
+       if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS))
+               send_sigtrap(tsk, regs, error_code, si_code);
        preempt_conditional_cli(regs);
-       return;
 
-#ifdef CONFIG_X86_32
-debug_vm86:
-       /* reenable preemption: handle_vm86_trap() might sleep */
-       dec_preempt_count();
-       handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code, 1);
-       conditional_cli(regs);
-       return;
-#endif
-
-clear_TF_reenable:
-       set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
-       regs->flags &= ~X86_EFLAGS_TF;
-       preempt_conditional_cli(regs);
        return;
 }