[PATCH] tracing: Fix clang -Wint-in-bool-context warnings in IF_ASSIGN macro

[PATCH] tracing: Fix clang -Wint-in-bool-context warnings in IF_ASSIGN macro

[Nathan Chancellor]

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.

Add the implicit '!= 0' to the WARN_ON statement to fix the warnings.

Link: https://github.com/llvm/llvm-project/commit/28b38c277a2941e9e891b2db30652cfd962f070b
Link: https://github.com/ClangBuiltLinux/linux/issues/686
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 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

Re: [PATCH] tracing: Fix clang -Wint-in-bool-context warnings in IF_ASSIGN macro

[Nick Desaulniers]

On Wed, Sep 25, 2019 at 10:29 AM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> 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.
>
> Add the implicit '!= 0' to the WARN_ON statement to fix the warnings.
>
> Link: https://github.com/llvm/llvm-project/commit/28b38c277a2941e9e891b2db30652cfd962f070b
> Link: https://github.com/ClangBuiltLinux/linux/issues/686
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>

I can't think of a case that this warning is a bug (maybe David can
explain more), but seems like a small fix that can stop a big spew of
warnings, and IIUC this is the lone instance we see in the kernel.  In
that case, I prefer a tiny change to outright disabling the warning in
case it does find interesting cases later.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  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
>


-- 
Thanks,
~Nick Desaulniers

Re: [PATCH] tracing: Fix clang -Wint-in-bool-context warnings in IF_ASSIGN macro

[Dávid Bolvanský]

GCC C frontend does not warn, GCC C++ FE does. https://godbolt.org/z/_sczyM

So I (we?) think there is something weird in gcc frontends.

>> I can't think of a case that this warning is a bug (maybe David can
explain more),

In this case or generally? General bug example:

if (state == A || B)

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

Since this is just one occurrence and I recommend to just land this small fix.


st 25. 9. 2019 o 19:41 Nick Desaulniers <ndesaulniers@google.com> napísal(a):
>
> On Wed, Sep 25, 2019 at 10:29 AM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > 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.
> >
> > Add the implicit '!= 0' to the WARN_ON statement to fix the warnings.
> >
> > Link: https://github.com/llvm/llvm-project/commit/28b38c277a2941e9e891b2db30652cfd962f070b
> > Link: https://github.com/ClangBuiltLinux/linux/issues/686
> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
>
> I can't think of a case that this warning is a bug (maybe David can
> explain more), but seems like a small fix that can stop a big spew of
> warnings, and IIUC this is the lone instance we see in the kernel.  In
> that case, I prefer a tiny change to outright disabling the warning in
> case it does find interesting cases later.
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>
> > ---
> >  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
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers

Re: [PATCH] tracing: Fix clang -Wint-in-bool-context warnings in IF_ASSIGN macro

[Steven Rostedt]

On Thu, 26 Sep 2019 01:37:29 +0200
Dávid Bolvanský <david.bolvansky@gmail.com> wrote:

> GCC C frontend does not warn, GCC C++ FE does. https://godbolt.org/z/_sczyM
> 
> So I (we?) think there is something weird in gcc frontends.
> 
> >> I can't think of a case that this warning is a bug (maybe David can  
> explain more),
> 
> In this case or generally? General bug example:
> 
> if (state == A || B)
> 
> (should be if (state == A || state == B))
> 
> Since this is just one occurrence and I recommend to just land this small
> fix.
> 

Can we add the above comment to the commit log. I was stuck on
wondering what was wrong with the original code, and was ignoring the
patch because I couldn't see what was wrong.

-- Steve

[PATCH v2] tracing: Fix clang -Wint-in-bool-context warnings in IF_ASSIGN macro

[Nathan Chancellor]

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@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.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