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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: mmotm/arch/x86/kernel/traps.c
===================================================================
--- mmotm.orig/arch/x86/kernel/traps.c
+++ mmotm/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 */

/* Catch kmemcheck conditions first of all! */
if (condition & DR_STEP && kmemcheck_trap(regs))
@@ -585,61 +586,42 @@ 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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