Commit 10faa81e authored by Roland McGrath's avatar Roland McGrath Committed by Ingo Molnar
Browse files

x86: debugctlmsr arch_has_block_step 



This implements user-mode step-until-branch on x86 using the BTF bit
in MSR_IA32_DEBUGCTLMSR.  It's just like single-step, only less so.

Signed-off-by: default avatarRoland McGrath <roland@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 7e991604

arch/x86/kernel/step.c

+61 −3
Original line number Diff line number Diff line
@@ -107,7 +107,10 @@ static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs) 
	return 0;

}



void user_enable_single_step(struct task_struct *child)

/*

 * Enable single-stepping.  Return nonzero if user mode is not using TF itself.

 */

static int enable_single_step(struct task_struct *child)

{

	struct pt_regs *regs = task_pt_regs(child);
@@ -122,7 +125,7 @@ void user_enable_single_step(struct task_struct *child) 
	 * If TF was already set, don't do anything else

	 */

	if (regs->eflags & X86_EFLAGS_TF)

		return;

		return 0;



	/* Set TF on the kernel stack.. */

	regs->eflags |= X86_EFLAGS_TF;
@@ -133,13 +136,68 @@ void user_enable_single_step(struct task_struct *child) 
	 * won't clear it by hand later.

	 */

	if (is_setting_trap_flag(child, regs))

		return;

		return 0;



	set_tsk_thread_flag(child, TIF_FORCED_TF);



	return 1;

}



/*

 * Install this value in MSR_IA32_DEBUGCTLMSR whenever child is running.

 */

static void write_debugctlmsr(struct task_struct *child, unsigned long val)

{

	child->thread.debugctlmsr = val;



	if (child != current)

		return;



#ifdef CONFIG_X86_64

	wrmsrl(MSR_IA32_DEBUGCTLMSR, val);

#else

	wrmsr(MSR_IA32_DEBUGCTLMSR, val, 0);

#endif

}



/*

 * Enable single or block step.

 */

static void enable_step(struct task_struct *child, bool block)

{

	/*

	 * Make sure block stepping (BTF) is not enabled unless it should be.

	 * Note that we don't try to worry about any is_setting_trap_flag()

	 * instructions after the first when using block stepping.

	 * So noone should try to use debugger block stepping in a program

	 * that uses user-mode single stepping itself.

	 */

	if (enable_single_step(child) && block) {

		set_tsk_thread_flag(child, TIF_DEBUGCTLMSR);

		write_debugctlmsr(child, DEBUGCTLMSR_BTF);

	} else if (test_and_clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR)) {

		write_debugctlmsr(child, 0);

	}

}



void user_enable_single_step(struct task_struct *child)

{

	enable_step(child, 0);

}



void user_enable_block_step(struct task_struct *child)

{

	enable_step(child, 1);

}



void user_disable_single_step(struct task_struct *child)

{

	/*

	 * Make sure block stepping (BTF) is disabled.

	 */

	if (test_and_clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR))

		write_debugctlmsr(child, 0);



	/* Always clear TIF_SINGLESTEP... */

	clear_tsk_thread_flag(child, TIF_SINGLESTEP);

arch/x86/kernel/traps_32.c

+6 −0
Original line number Diff line number Diff line
@@ -837,6 +837,12 @@ fastcall void __kprobes do_debug(struct pt_regs * regs, long error_code) 


	get_debugreg(condition, 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,

					SIGTRAP) == NOTIFY_STOP)

		return;

arch/x86/kernel/traps_64.c

+6 −0
Original line number Diff line number Diff line
@@ -850,6 +850,12 @@ asmlinkage void __kprobes do_debug(struct pt_regs * regs, 


	get_debugreg(condition, 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,

						SIGTRAP) == NOTIFY_STOP)

		return;

include/asm-x86/ptrace.h

+7 −0
Original line number Diff line number Diff line
@@ -150,6 +150,13 @@ enum { 
extern void user_enable_single_step(struct task_struct *);

extern void user_disable_single_step(struct task_struct *);



extern void user_enable_block_step(struct task_struct *);

#ifdef CONFIG_X86_DEBUGCTLMSR

#define arch_has_block_step()	(1)

#else

#define arch_has_block_step()	(boot_cpu_data.x86 >= 6)

#endif



struct user_desc;

extern int do_get_thread_area(struct task_struct *p, int idx,

			      struct user_desc __user *info);