Add arch_ptrace_stop

This adds support to allow asm/ptrace.h to define two new macros,
arch_ptrace_stop_needed and arch_ptrace_stop.  These control special
machine-specific actions to be done before a ptrace stop.  The new code
compiles away to nothing when the new macros are not defined.  This is the
case on all machines to begin with.

On ia64, these macros will be defined to solve the long-standing issue of
ptrace vs register backing store.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Petr Tesarik <ptesarik@suse.cz>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Matthew Wilcox <willy@debian.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 515bff053de8..6ab80714a916 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -204,6 +204,41 @@ static inline void user_enable_block_step(struct task_struct *task)
 }
 #endif  /* arch_has_block_step */
 
+#ifndef arch_ptrace_stop_needed
+/**
+ * arch_ptrace_stop_needed - Decide whether arch_ptrace_stop() should be called
+ * @code:       current->exit_code value ptrace will stop with
+ * @info:       siginfo_t pointer (or %NULL) for signal ptrace will stop with
+ *
+ * This is called with the siglock held, to decide whether or not it's
+ * necessary to release the siglock and call arch_ptrace_stop() with the
+ * same @code and @info arguments.  It can be defined to a constant if
+ * arch_ptrace_stop() is never required, or always is.  On machines where
+ * this makes sense, it should be defined to a quick test to optimize out
+ * calling arch_ptrace_stop() when it would be superfluous.  For example,
+ * if the thread has not been back to user mode since the last stop, the
+ * thread state might indicate that nothing needs to be done.
+ */
+#define arch_ptrace_stop_needed(code, info)     (0)
+#endif
+
+#ifndef arch_ptrace_stop
+/**
+ * arch_ptrace_stop - Do machine-specific work before stopping for ptrace
+ * @code:       current->exit_code value ptrace will stop with
+ * @info:       siginfo_t pointer (or %NULL) for signal ptrace will stop with
+ *
+ * This is called with no locks held when arch_ptrace_stop_needed() has
+ * just returned nonzero.  It is allowed to block, e.g. for user memory
+ * access.  The arch can have machine-specific work to be done before
+ * ptrace stops.  On ia64, register backing store gets written back to user
+ * memory here.  Since this can be costly (requires dropping the siglock),
+ * we only do it when the arch requires it for this particular stop, as
+ * indicated by arch_ptrace_stop_needed().
+ */
+#define arch_ptrace_stop(code, info)            do { } while (0)
+#endif
+
 #endif
 
 #endif