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    Subject[PATCH 5.17 329/343] x86/bug: Prevent shadowing in __WARN_FLAGS
    Date
    From: Vincent Mailhol <mailhol.vincent@wanadoo.fr>

    commit 9ce02f0fc68326dd1f87a0a3a4c6ae7fdd39e6f6 upstream.

    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@mail.gmail.com/

    [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

    Fixes: bfb1a7c91fb7 ("x86/bug: Merge annotate_reachable() into_BUG_FLAGS() asm")
    Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
    Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
    Link: https://lkml.kernel.org/r/20220324023742.106546-1-mailhol.vincent@wanadoo.fr
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/include/asm/bug.h | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- 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)


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