Merge branch 'perf/core' into perf/uprobes

[~andy/linux] / arch / tile / lib / memcpy_user_64.c

diff --git a/arch/tile/lib/memcpy_user_64.c b/arch/tile/lib/memcpy_user_64.c
index 4763b3aff1cc7695f340aae288e913a79a02f6ea..37440caa7370fe3d4c052086c6143bb6ab8e583c 100644 (file)
--- a/arch/tile/lib/memcpy_user_64.c
+++ b/arch/tile/lib/memcpy_user_64.c
@@ -14,7 +14,13 @@
  * Do memcpy(), but trap and return "n" when a load or store faults.
  *
  * Note: this idiom only works when memcpy() compiles to a leaf function.
- * If "sp" is updated during memcpy, the "jrp lr" will be incorrect.
+ * Here leaf function not only means it does not have calls, but also
+ * requires no stack operations (sp, stack frame pointer) and no
+ * use of callee-saved registers, else "jrp lr" will be incorrect since
+ * unwinding stack frame is bypassed. Since memcpy() is not complex so
+ * these conditions are satisfied here, but we need to be careful when
+ * modifying this file. This is not a clean solution but is the best
+ * one so far.
  *
  * Also note that we are capturing "n" from the containing scope here.
  */