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branch-check: fix long->int truncation when profiling branches

PATCH In review Mikulas Patocka 1 participant 1 message May 30, 2018

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Mikulas Patocka

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PATCH 3/4 branch-check: fix long->int truncation when profiling branches

The function __builtin_expect returns long type (see the gcc documentation), and so do macros likely and unlikely. Unfortunatelly, when CONFIG_PROFILE_ANNOTATED_BRANCHES is selected, the macros likely and unlikely expand to __branch_check__ and __branch_check__ truncates the long type to int. This unintended truncation may cause bugs in various kernel code (we found a bug in dm-writecache because of it), so it's better to fix __branch_check__ to return long.

---
 include/linux/compiler.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
include/linux/compiler.h +1 -1
Index: linux-2.6/include/linux/compiler.h
===================================================================
@@ -21,7 +21,7 @@ void ftrace_likely_update(struct ftrace_
 #define unlikely_notrace(x)	__builtin_expect(!!(x), 0)
 
 #define __branch_check__(x, expect, is_constant) ({			\
-			int ______r;					\
+			long ______r;					\
 			static struct ftrace_likely_data		\
 				__attribute__((__aligned__(4)))		\
 				__attribute__((section("_ftrace_annotated_branch"))) \