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
Link: http://lkml.kernel.org/r/20190926162258.466321-1-natechancellor@gmail.com
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 26b0a08f3c7d46e9359f2c6fef83f67edceed031..f801d154ff6a3bb71950c215d8598c9a9a5acbe0 100644 (file)
--- 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. */