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, GCC would yield: | 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) | | ~~~~~~~~~~~~~~~^ For reference, sparse also warns about it, c.f. [1]. This patch renames the variable from f to __flags (with two underscore prefixes as suggested in the Linux kernel coding style [2]) in order to prevent collisions. [1] https://lore.kernel.org/all/CAFGhKbyifH1a+nAMCvWM88TK6fpNPdzFtUXPmRGnnQeePV+1sw@xxxxxxxxxxxxxx/ [2] 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/latest/process/coding-style.html#macros-enums-and-rtl CC: Charlemagne Lasse <charlemagnelasse@xxxxxxxxx> Fixes: bfb1a7c91fb7 ("x86/bug: Merge annotate_reachable() into_BUG_FLAGS() asm") Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> --- Changelog: v2 -> v3: * add a mention that sparse is warning about this too. c.f. https://lore.kernel.org/all/CAKwvOdmSV3Nse+tGMBXvN=QvnOs6-ODZRJB0OF5Pd6BVb-scFw@xxxxxxxxxxxxxx/ v1 -> v2: * Update the reference link to the kernel documentation to latest version. * Do not break the Fixes: tag to a new line. * Added the Acked-by and Reviewed-by tags. --- arch/x86/include/asm/bug.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h index bab883c0b6fe..66570e95af39 100644 --- a/arch/x86/include/asm/bug.h +++ b/arch/x86/include/asm/bug.h @@ -77,9 +77,9 @@ do { \ */ #define __WARN_FLAGS(flags) \ do { \ - __auto_type f = BUGFLAG_WARNING|(flags); \ + __auto_type __flags = BUGFLAG_WARNING|(flags); \ instrumentation_begin(); \ - _BUG_FLAGS(ASM_UD2, f, ASM_REACHABLE); \ + _BUG_FLAGS(ASM_UD2, __flags, ASM_REACHABLE); \ instrumentation_end(); \ } while (0) -- 2.34.1
