[PATCH v2 1/3] compiler.h: define __no_initialize

[glider@google.com]

For CONFIG_INIT_STACK_ALL it's sometimes handy to disable
force-initialization for a local variable, if it is known to be initialized
later on before the first use. This can be done by using the
__no_initialize macro.

__no_initialize should be applied carefully, as future changes to
the code around the local variable may introduce paths on which the
variable remains uninitialized before the use.

Signed-off-by: Alexander Potapenko <glider@google.com>

---

v2:
 - changed __do_not_initialize to __no_initialize as requested by Kees
   Cook
---
 include/linux/compiler-clang.h | 10 ++++++++++
 include/linux/compiler_types.h |  4 ++++
 2 files changed, 14 insertions(+)

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index 333a6695a918c..27f774b27b061 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -24,6 +24,16 @@
 #define __no_sanitize_address
 #endif
 
+/*
+ * Disable initialization of a local variable when building with
+ * CONFIG_INIT_STACK_ALL.
+ */
+#ifdef CONFIG_INIT_STACK_ALL
+#define __no_initialize __attribute__((uninitialized))
+#else
+#define __no_initialize
+#endif
+
 /*
  * Not all versions of clang implement the the type-generic versions
  * of the builtin overflow checkers. Fortunately, clang implements
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 72393a8c1a6c5..0208699c855af 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -216,6 +216,10 @@ struct ftrace_likely_data {
 # define __no_fgcse
 #endif
 
+#ifndef __no_initialize
+#define __no_initialize
+#endif
+
 /* Are two types/vars the same type (ignoring qualifiers)? */
 #define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
 
-- 
2.25.0.265.gbab2e86ba0-goog