[PATCH] x86_64: clean up ptrace single-stepping

Ported from i386 (originally from Linus)

clean up ptrace single-stepping, make PT_DTRACE exact.
  
  (This makes the naming of "DTRACE" purely historical, since
  on x86 it now means "single step in progress").

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 50 insertions, 29 deletions

diff --git a/arch/x86_64/kernel/ptrace.c b/arch/x86_64/kernel/ptrace.c
index 0b7b101debdf..002237c3b6a2 100644
--- a/arch/x86_64/kernel/ptrace.c
+++ b/arch/x86_64/kernel/ptrace.c
@@ -63,6 +63,12 @@ static inline unsigned long get_stack_long(struct task_struct *task, int offset)
         return (*((unsigned long *)stack));
 }
 
+static inline struct pt_regs *get_child_regs(struct task_struct *task)
+{
+        struct pt_regs *regs = (void *)task->thread.rsp0;
+        return regs - 1;
+}
+
 /*
  * this routine will put a word on the processes privileged stack. 
  * the offset is how far from the base addr as stored in the TSS.  
@@ -80,6 +86,42 @@ static inline long put_stack_long(struct task_struct *task, int offset,
         return 0;
 }
 
+static void set_singlestep(struct task_struct *child)
+{
+        struct pt_regs *regs = get_child_regs(child);
+
+        /*
+         * Always set TIF_SINGLESTEP - this guarantees that
+         * we single-step system calls etc..  This will also
+         * cause us to set TF when returning to user mode.
+         */
+        set_tsk_thread_flag(child, TIF_SINGLESTEP);
+
+        /*
+         * If TF was already set, don't do anything else
+         */
+        if (regs->eflags & TRAP_FLAG)
+                return;
+
+        /* Set TF on the kernel stack.. */
+        regs->eflags |= TRAP_FLAG;
+
+        child->ptrace |= PT_DTRACE;
+}
+
+static void clear_singlestep(struct task_struct *child)
+{
+        /* Always clear TIF_SINGLESTEP... */
+        clear_tsk_thread_flag(child, TIF_SINGLESTEP);
+
+        /* But touch TF only if it was set by us.. */
+        if (child->ptrace & PT_DTRACE) {
+                struct pt_regs *regs = get_child_regs(child);
+                regs->eflags &= ~TRAP_FLAG;
+                child->ptrace &= ~PT_DTRACE;
+        }
+}
+
 /*
  * Called by kernel/ptrace.c when detaching..
  *
@@ -87,11 +129,7 @@ static inline long put_stack_long(struct task_struct *task, int offset,
  */
 void ptrace_disable(struct task_struct *child)
 { 
-        long tmp;
-
-        clear_tsk_thread_flag(child, TIF_SINGLESTEP);
-        tmp = get_stack_long(child, EFL_OFFSET) & ~TRAP_FLAG;
-        put_stack_long(child, EFL_OFFSET, tmp);
+        clear_singlestep(child);
 }
 
 static int putreg(struct task_struct *child,
@@ -338,8 +376,7 @@ asmlinkage long sys_ptrace(long request, long pid, unsigned long addr, long data
                 }
                 break;
         case PTRACE_SYSCALL: /* continue and stop at next (return from) syscall */
-        case PTRACE_CONT: { /* restart after signal. */
-                long tmp;
+        case PTRACE_CONT:    /* restart after signal. */
 
                 ret = -EIO;
                 if ((unsigned long) data > _NSIG)
@@ -350,14 +387,11 @@ asmlinkage long sys_ptrace(long request, long pid, unsigned long addr, long data
                         clear_tsk_thread_flag(child,TIF_SYSCALL_TRACE);
                 clear_tsk_thread_flag(child, TIF_SINGLESTEP);
                 child->exit_code = data;
-        /* make sure the single step bit is not set. */
-                tmp = get_stack_long(child, EFL_OFFSET);
-                tmp &= ~TRAP_FLAG;
-                put_stack_long(child, EFL_OFFSET,tmp);
+                /* make sure the single step bit is not set. */
+                clear_singlestep(child);
                 wake_up_process(child);
                 ret = 0;
                 break;
-        }
 
 #ifdef CONFIG_IA32_EMULATION
                 /* This makes only sense with 32bit programs. Allow a
@@ -394,41 +428,28 @@ asmlinkage long sys_ptrace(long request, long pid, unsigned long addr, long data
  * perhaps it should be put in the status that it wants to 
  * exit.
  */
-        case PTRACE_KILL: {
-                long tmp;
-
+        case PTRACE_KILL:
                 ret = 0;
                 if (child->exit_state == EXIT_ZOMBIE)   /* already dead */
                         break;
                 clear_tsk_thread_flag(child, TIF_SINGLESTEP);
                 child->exit_code = SIGKILL;
                 /* make sure the single step bit is not set. */
-                tmp = get_stack_long(child, EFL_OFFSET) & ~TRAP_FLAG;
-                put_stack_long(child, EFL_OFFSET, tmp);
+                clear_singlestep(child);
                 wake_up_process(child);
                 break;
-        }
-
-        case PTRACE_SINGLESTEP: {  /* set the trap flag. */
-                long tmp;
 
+        case PTRACE_SINGLESTEP:    /* set the trap flag. */
                 ret = -EIO;
                 if ((unsigned long) data > _NSIG)
                         break;
                 clear_tsk_thread_flag(child,TIF_SYSCALL_TRACE);
-                if ((child->ptrace & PT_DTRACE) == 0) {
-                        /* Spurious delayed TF traps may occur */
-                        child->ptrace |= PT_DTRACE;
-                }
-                tmp = get_stack_long(child, EFL_OFFSET) | TRAP_FLAG;
-                put_stack_long(child, EFL_OFFSET, tmp);
-                set_tsk_thread_flag(child, TIF_SINGLESTEP);
+                set_singlestep(child);
                 child->exit_code = data;
                 /* give it a chance to run. */
                 wake_up_process(child);
                 ret = 0;
                 break;
-        }
 
         case PTRACE_DETACH:
                 /* detach a process that was attached. */