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>

1 files changed, 24 insertions, 45 deletions

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index a1d288327ff0..de9913247dd0 100644
--- 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;
 }