linux-kernel - [PATCH v2] tracing: Fix clang -Wint-in-bool-context warnings in IF

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Date:   Thu, 26 Sep 2019 09:22:59 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        David Bolvansky <david.bolvansky@...il.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH v2] tracing: Fix clang -Wint-in-bool-context warnings in IF_ASSIGN macro

After r372664 in clang, the IF_ASSIGN macro causes a couple hundred
warnings along the lines of:

kernel/trace/trace_output.c:1331:2: warning: converting the enum
constant to a boolean [-Wint-in-bool-context]
kernel/trace/trace.h:409:3: note: expanded from macro
'trace_assign_type'
                IF_ASSIGN(var, ent, struct ftrace_graph_ret_entry,
                ^
kernel/trace/trace.h:371:14: note: expanded from macro 'IF_ASSIGN'
                WARN_ON(id && (entry)->type != id);     \
                           ^
264 warnings generated.

This warning can catch issues with constructs like:

    if (state == A || B)

where the developer really meant:

    if (state == A || state == B)

This is currently the only occurrence of the warning in the kernel
tree across defconfig, allyesconfig, allmodconfig for arm32, arm64,
and x86_64. Add the implicit '!= 0' to the WARN_ON statement to fix
the warnings and find potential issues in the future.

Link: https://github.com/llvm/llvm-project/commit/28b38c277a2941e9e891b2db30652cfd962f070b
Link: https://github.com/ClangBuiltLinux/linux/issues/686
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
---

v1 -> v2:

* Update commit message to give context behind the warning and explain
  this is currently the only occurrence of this warning in the tree.
* Add Nick's Reviewed-by tag.

 kernel/trace/trace.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 26b0a08f3c7d..f801d154ff6a 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -365,11 +365,11 @@ static inline struct trace_array *top_trace_array(void)
 	__builtin_types_compatible_p(typeof(var), type *)
 
 #undef IF_ASSIGN
-#define IF_ASSIGN(var, entry, etype, id)		\
-	if (FTRACE_CMP_TYPE(var, etype)) {		\
-		var = (typeof(var))(entry);		\
-		WARN_ON(id && (entry)->type != id);	\
-		break;					\
+#define IF_ASSIGN(var, entry, etype, id)			\
+	if (FTRACE_CMP_TYPE(var, etype)) {			\
+		var = (typeof(var))(entry);			\
+		WARN_ON(id != 0 && (entry)->type != id);	\
+		break;						\
 	}
 
 /* Will cause compile errors if type is not found. */
-- 
2.23.0