On Mon, Nov 25, 2024 at 09:18:18AM -0500, Mathieu Desnoyers wrote:
> On 2024-11-23 12:38, Linus Torvalds wrote:
> I tried the following alteration to the code, which triggers an
> unexpected compiler warning on master, but not on v6.12. I suspect
> this is something worth discussing:
>
> static inline void trace_##name(proto) \
> { \
> if (static_branch_unlikely(&__tracepoint_##name.key)) { \
> if (cond) \
> scoped_guard(preempt_notrace) \
> __DO_TRACE_CALL(name, TP_ARGS(args)); \
So coding style would like braces here for it being multi-line. As
opposed to C that only mandates it for multi-statement. And then the
problem doesn't occur.
> } \
> if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \
> WARN_ONCE(!rcu_is_watching(), \
> "RCU not watching for tracepoint"); \
> } \
> }
>
> I suspect this is caused by the "else" at the end of the __scoped_guard() macro:
>
> #define __scoped_guard(_name, _label, args...) \
> for (CLASS(_name, scope)(args); \
> __guard_ptr(_name)(&scope) || !__is_cond_ptr(_name); \
> ({ goto _label; })) \
> if (0) { \
> _label: \
> break; \
> } else
>
> #define scoped_guard(_name, args...) \
> __scoped_guard(_name, __UNIQUE_ID(label), args)
>
> AFAIU this is a new warning introduced by
>
> commit fcc22ac5baf ("cleanup: Adjust scoped_guard() macros to avoid potential warning")
Yeah,.. So strictly speaking the code is fine, but the various compilers
don't like it when that else dangles :/
