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, 2 insertions, 0 deletions

diff --git a/include/asm-x86/thread_info_32.h b/include/asm-x86/thread_info_32.h
index a516e9192f11..009ecc6ad38b 100644
--- a/include/asm-x86/thread_info_32.h
+++ b/include/asm-x86/thread_info_32.h
@@ -138,6 +138,7 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_IO_BITMAP           18      /* uses I/O bitmap */
 #define TIF_FREEZE              19      /* is freezing for suspend */
 #define TIF_NOTSC               20      /* TSC is not accessible in userland */
+#define TIF_FORCED_TF           21      /* true if TF in eflags artificially */
 
 #define _TIF_SYSCALL_TRACE      (1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING         (1<<TIF_SIGPENDING)
@@ -153,6 +154,7 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_IO_BITMAP          (1<<TIF_IO_BITMAP)
 #define _TIF_FREEZE             (1<<TIF_FREEZE)
 #define _TIF_NOTSC              (1<<TIF_NOTSC)
+#define _TIF_FORCED_TF          (1<<TIF_FORCED_TF)
 
 /* work to do on interrupt/exception return */
 #define _TIF_WORK_MASK \