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x86: debugctlmsr arch_has_block_step

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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: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Roland McGrath
2008-01-30 13:30:54 +01:00
committed by Ingo Molnar
parent 7e9916040b
commit 10faa81e10
4 changed files with 80 additions and 3 deletions
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64
arch/x86/kernel/step.c
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@@ -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);