x86: user_regset helpers

This adds some inlines to linux/regset.h intended for arch code to use in
its user_regset get and set functions.  These make it pretty easy to deal
with the interface's optional kernel-space or user-space pointers and its
generalized access to a part of the register data at a time.

In simple cases where the internal data structure matches the exported
layout (core dump format), a get function can be nothing but a call to
user_regset_copyout, and a set function a call to user_regset_copyin.

In other cases the exported layout is usually made up of a few pieces each
stored contiguously in a different internal data structure.  These helpers
make it straightforward to write a get or set function by processing each
contiguous chunk of the data in order.  The start_pos and end_pos arguments
are always constants, so these inlines collapse to a small amount of code.

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, 116 insertions, 0 deletions

diff --git a/include/linux/regset.h b/include/linux/regset.h
index 85d0fb0a014d..761c931af975 100644
--- a/include/linux/regset.h
+++ b/include/linux/regset.h
@@ -15,6 +15,7 @@
 
 #include <linux/compiler.h>
 #include <linux/types.h>
+#include <linux/uaccess.h>
 struct task_struct;
 struct user_regset;
 
@@ -203,4 +204,119 @@ struct user_regset_view {
 const struct user_regset_view *task_user_regset_view(struct task_struct *tsk);
 
 
+/*
+ * These are helpers for writing regset get/set functions in arch code.
+ * Because @start_pos and @end_pos are always compile-time constants,
+ * these are inlined into very little code though they look large.
+ *
+ * Use one or more calls sequentially for each chunk of regset data stored
+ * contiguously in memory.  Call with constants for @start_pos and @end_pos,
+ * giving the range of byte positions in the regset that data corresponds
+ * to; @end_pos can be -1 if this chunk is at the end of the regset layout.
+ * Each call updates the arguments to point past its chunk.
+ */
+
+static inline int user_regset_copyout(unsigned int *pos, unsigned int *count,
+                                      void **kbuf,
+                                      void __user **ubuf, const void *data,
+                                      const int start_pos, const int end_pos)
+{
+        if (*count == 0)
+                return 0;
+        BUG_ON(*pos < start_pos);
+        if (end_pos < 0 || *pos < end_pos) {
+                unsigned int copy = (end_pos < 0 ? *count
+                                     : min(*count, end_pos - *pos));
+                data += *pos - start_pos;
+                if (*kbuf) {
+                        memcpy(*kbuf, data, copy);
+                        *kbuf += copy;
+                } else if (__copy_to_user(*ubuf, data, copy))
+                        return -EFAULT;
+                else
+                        *ubuf += copy;
+                *pos += copy;
+                *count -= copy;
+        }
+        return 0;
+}
+
+static inline int user_regset_copyin(unsigned int *pos, unsigned int *count,
+                                     const void **kbuf,
+                                     const void __user **ubuf, void *data,
+                                     const int start_pos, const int end_pos)
+{
+        if (*count == 0)
+                return 0;
+        BUG_ON(*pos < start_pos);
+        if (end_pos < 0 || *pos < end_pos) {
+                unsigned int copy = (end_pos < 0 ? *count
+                                     : min(*count, end_pos - *pos));
+                data += *pos - start_pos;
+                if (*kbuf) {
+                        memcpy(data, *kbuf, copy);
+                        *kbuf += copy;
+                } else if (__copy_from_user(data, *ubuf, copy))
+                        return -EFAULT;
+                else
+                        *ubuf += copy;
+                *pos += copy;
+                *count -= copy;
+        }
+        return 0;
+}
+
+/*
+ * These two parallel the two above, but for portions of a regset layout
+ * that always read as all-zero or for which writes are ignored.
+ */
+static inline int user_regset_copyout_zero(unsigned int *pos,
+                                           unsigned int *count,
+                                           void **kbuf, void __user **ubuf,
+                                           const int start_pos,
+                                           const int end_pos)
+{
+        if (*count == 0)
+                return 0;
+        BUG_ON(*pos < start_pos);
+        if (end_pos < 0 || *pos < end_pos) {
+                unsigned int copy = (end_pos < 0 ? *count
+                                     : min(*count, end_pos - *pos));
+                if (*kbuf) {
+                        memset(*kbuf, 0, copy);
+                        *kbuf += copy;
+                } else if (__clear_user(*ubuf, copy))
+                        return -EFAULT;
+                else
+                        *ubuf += copy;
+                *pos += copy;
+                *count -= copy;
+        }
+        return 0;
+}
+
+static inline int user_regset_copyin_ignore(unsigned int *pos,
+                                            unsigned int *count,
+                                            const void **kbuf,
+                                            const void __user **ubuf,
+                                            const int start_pos,
+                                            const int end_pos)
+{
+        if (*count == 0)
+                return 0;
+        BUG_ON(*pos < start_pos);
+        if (end_pos < 0 || *pos < end_pos) {
+                unsigned int copy = (end_pos < 0 ? *count
+                                     : min(*count, end_pos - *pos));
+                if (*kbuf)
+                        *kbuf += copy;
+                else
+                        *ubuf += copy;
+                *pos += copy;
+                *count -= copy;
+        }
+        return 0;
+}
+
+
 #endif  /* <linux/regset.h> */