Messages in this thread | | | From | Vincent MAILHOL <> | Date | Sat, 5 Mar 2022 12:57:50 +0900 | Subject | Re: [PATCH] x86/bug: __WARN_FLAGS: prevent shadowing by renaming local variable f to __flags |
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On Tue. 5 Mar 2022 à 04:26, Nick Desaulniers <ndesaulniers@google.com> wrote: > On Thu, Mar 3, 2022 at 3:08 AM Vincent Mailhol > <mailhol.vincent@wanadoo.fr> wrote: > > The macro __WARN_FLAGS() uses a local variable named "f". This being a > > common name, there is a risk of shadowing other variables. > > > > For example: > > > > | In file included from ./include/linux/bug.h:5, > > | from ./include/linux/cpumask.h:14, > > | from ./arch/x86/include/asm/cpumask.h:5, > > | from ./arch/x86/include/asm/msr.h:11, > > | from ./arch/x86/include/asm/processor.h:22, > > | from ./arch/x86/include/asm/timex.h:5, > > | from ./include/linux/timex.h:65, > > | from ./include/linux/time32.h:13, > > | from ./include/linux/time.h:60, > > | from ./include/linux/stat.h:19, > > | from ./include/linux/module.h:13, > > | from virt/lib/irqbypass.mod.c:1: > > | ./include/linux/rcupdate.h: In function 'rcu_head_after_call_rcu': > > | ./arch/x86/include/asm/bug.h:80:21: warning: declaration of 'f' shadows a parameter [-Wshadow] > > | 80 | __auto_type f = BUGFLAG_WARNING|(flags); \ > > | | ^ > > | ./include/asm-generic/bug.h:106:17: note: in expansion of macro '__WARN_FLAGS' > > | 106 | __WARN_FLAGS(BUGFLAG_ONCE | \ > > | | ^~~~~~~~~~~~ > > | ./include/linux/rcupdate.h:1007:9: note: in expansion of macro 'WARN_ON_ONCE' > > | 1007 | WARN_ON_ONCE(func != (rcu_callback_t)~0L); > > | | ^~~~~~~~~~~~ > > | In file included from ./include/linux/rbtree.h:24, > > | from ./include/linux/mm_types.h:11, > > | from ./include/linux/buildid.h:5, > > | from ./include/linux/module.h:14, > > | from virt/lib/irqbypass.mod.c:1: > > | ./include/linux/rcupdate.h:1001:62: note: shadowed declaration is here > > | 1001 | rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) > > | | ~~~~~~~~~~~~~~~^ > > > > This patch renames the variable from f to __flags (with two underscore > > prefixes as suggested in the Linux kernel coding style [1]) in order > > to prevent collisions. > > > > [1] Linux kernel coding style, section 12) Macros, Enums and RTL, > > paragraph 5) namespace collisions when defining local variables in > > macros resembling functions > > https://www.kernel.org/doc/html/v4.10/process/coding-style.html#macros-enums-and-rtl
Indeed! Will update this in v2 (and will also fix the Fixes: tag as pointed by Josh).
> Ah, thanks for the patch. I missed that coding style recommendation. > Might want to link to a newer (or evergreen) version of the docs > though: > https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl > Not sure what happens when we start shadowing variables named __flags, > but maybe we cross that bridge if/when we get there.
Ack.
> Thanks for the fix! > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
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