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Subject[RFC Patch 3/9] 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_32.c | 67 ++++++++++++++++-----------------------------
arch/x86/kernel/traps_64.c | 64 ++++++++++++++++++++----------------------
2 files changed, 54 insertions(+), 77 deletions(-)

Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/traps_32.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/traps_32.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/traps_32.c
@@ -890,11 +890,12 @@ void __kprobes do_int3(struct pt_regs *r
void __kprobes do_debug(struct pt_regs *regs, long error_code)
{
struct task_struct *tsk = current;
- unsigned int condition;
+ unsigned long dr6;

trace_hardirqs_fixup();

- 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.
@@ -902,60 +903,40 @@ void __kprobes do_debug(struct pt_regs *
clear_tsk_thread_flag(tsk, TIF_DEBUGCTLMSR);
tsk->thread.debugctlmsr = 0;

- if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
- SIGTRAP) == NOTIFY_STOP)
+ /* 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 */
if (regs->flags & X86_EFLAGS_IF)
local_irq_enable();

- /* 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;
}

- if (regs->flags & X86_VM_MASK)
- goto debug_vm86;
-
- /* 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) {
- /*
- * We already checked v86 mode above, so we can
- * check for kernel mode by just checking the CPL
- * of CS.
- */
- if (!user_mode(regs))
- goto clear_TF_reenable;
+ if ((dr6 & DR_STEP) && !user_mode(regs)) {
+ tsk->thread.vdr6 &= ~DR_STEP;
+ set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
+ regs->flags &= ~X86_EFLAGS_TF;
}

- /* Ok, finally something we can handle */
- send_sigtrap(tsk, regs, error_code);
-
- /*
- * Disable additional traps. They'll be re-enabled when
- * the signal is delivered.
- */
-clear_dr7:
- set_debugreg(0, 7);
- return;
-
-debug_vm86:
- handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code, 1);
- return;
-
-clear_TF_reenable:
- set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
- regs->flags &= ~X86_EFLAGS_TF;
- return;
+ if (tsk->thread.vdr6 & (DR_STEP|DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3))
+ send_sigtrap(tsk, regs, error_code);
}

+
/*
* Note that we play around with the 'TS' bit in an attempt to get
* the correct behaviour even in the presence of the asynchronous
Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/traps_64.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/traps_64.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/traps_64.c
@@ -894,13 +894,14 @@ asmlinkage __kprobes struct pt_regs *syn
asmlinkage void __kprobes do_debug(struct pt_regs * regs,
unsigned long error_code)
{
+ unsigned long dr6;;
struct task_struct *tsk = current;
- unsigned long condition;
siginfo_t info;

trace_hardirqs_fixup();

- 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.
@@ -908,48 +909,43 @@ asmlinkage void __kprobes do_debug(struc
clear_tsk_thread_flag(tsk, TIF_DEBUGCTLMSR);
tsk->thread.debugctlmsr = 0;

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

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;
}

- 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.vdr6 &= ~DR_STEP;
+ set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
+ regs->flags &= ~X86_EFLAGS_TF;
}

- /* Ok, finally something we can handle */
- tsk->thread.trap_no = 1;
- tsk->thread.error_code = error_code;
- info.si_signo = SIGTRAP;
- info.si_errno = 0;
- info.si_code = TRAP_BRKPT;
- info.si_addr = user_mode(regs) ? (void __user *)regs->ip : NULL;
- force_sig_info(SIGTRAP, &info, tsk);
-
-clear_dr7:
- set_debugreg(0, 7);
- preempt_conditional_cli(regs);
- return;
-
-clear_TF_reenable:
- set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
- regs->flags &= ~X86_EFLAGS_TF;
- preempt_conditional_cli(regs);
- return;
+ if (tsk->thread.vdr6 & (DR_STEP|DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)) {
+ tsk->thread.trap_no = 1;
+ tsk->thread.error_code = error_code;
+ info.si_signo = SIGTRAP;
+ info.si_errno = 0;
+ info.si_code = TRAP_BRKPT;
+ info.si_addr = user_mode(regs) ? (void __user *)regs->ip : NULL;
+ force_sig_info(SIGTRAP, &info, tsk);
+ }
}

static int kernel_math_error(struct pt_regs *regs, const char *str, int trapnr)

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