[PATCH 1/3] compiler.h: define __do_not_initialize

[glider at 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
__do_not_initialize macro.

__do_not_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 at google.com>
---
 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..9204334d39261 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 __do_not_initialize __attribute__((uninitialized))
+#else
+#define __do_not_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..b216beb5586fc 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -180,6 +180,10 @@ struct ftrace_likely_data {
 
 #endif /* __ASSEMBLY__ */
 
+#ifndef __do_not_initialize
+#define __do_not_initialize
+#endif
+
 /*
  * The below symbols may be defined for one or more, but not ALL, of the above
  * compilers. We don't consider that to be an error, so set them to nothing.
-- 
2.25.0.265.gbab2e86ba0-goog