x86 single_step: TIF_FORCED_TF

This changes the single-step support to use a new thread_info flag
TIF_FORCED_TF instead of the PT_DTRACE flag in task_struct.ptrace.
This keeps arch implementation uses out of this non-arch field.

This changes the ptrace access to eflags to mask TF and maintain
the TIF_FORCED_TF flag directly if userland sets TF, instead of
relying on ptrace_signal_deliver.  The 64-bit and 32-bit kernels
are harmonized on this same behavior.  The ptrace_signal_deliver
approach works now, but this change makes the low-level register
access code reliable when called from different contexts than a
ptrace stop, which will be possible in the future.

The 64-bit do_debug exception handler is also changed not to clear TF
from user-mode registers.  This matches the 32-bit kernel's behavior.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 18 insertions, 2 deletions

diff --git a/arch/x86/ia32/ptrace32.c b/arch/x86/ia32/ptrace32.c
index 9d754b640205..5dee33417313 100644
--- a/arch/x86/ia32/ptrace32.c
+++ b/arch/x86/ia32/ptrace32.c
@@ -89,6 +89,15 @@ static int putreg32(struct task_struct *child, unsigned regno, u32 val)
                 __u64 *flags = &stack[offsetof(struct pt_regs, eflags)/8];
 
                 val &= FLAG_MASK;
+                /*
+                 * If the user value contains TF, mark that
+                 * it was not "us" (the debugger) that set it.
+                 * If not, make sure it stays set if we had.
+                 */
+                if (val & X86_EFLAGS_TF)
+                        clear_tsk_thread_flag(child, TIF_FORCED_TF);
+                else if (test_tsk_thread_flag(child, TIF_FORCED_TF))
+                        val |= X86_EFLAGS_TF;
                 *flags = val | (*flags & ~FLAG_MASK);
                 break;
         }
@@ -179,9 +188,17 @@ static int getreg32(struct task_struct *child, unsigned regno, u32 *val)
         R32(eax, rax);
         R32(orig_eax, orig_rax);
         R32(eip, rip);
-        R32(eflags, eflags);
         R32(esp, rsp);
 
+        case offsetof(struct user32, regs.eflags):
+                /*
+                 * If the debugger set TF, hide it from the readout.
+                 */
+                *val = stack[offsetof(struct pt_regs, eflags)/8];
+                if (test_tsk_thread_flag(child, TIF_FORCED_TF))
+                        *val &= ~X86_EFLAGS_TF;
+                break;
+
         case offsetof(struct user32, u_debugreg[0]):
                 *val = child->thread.debugreg0;
                 break;
@@ -425,4 +442,3 @@ asmlinkage long sys32_ptrace(long request, u32 pid, u32 addr, u32 data)
         put_task_struct(child);
         return ret;
 }
-