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From:   Charlemagne Lasse <charlemagnelasse@gmail.com>
Date:   Wed, 23 Mar 2022 20:30:22 +0100
Message-ID: <CAFGhKbyifH1a+nAMCvWM88TK6fpNPdzFtUXPmRGnnQeePV+1sw@mail.gmail.com>
Subject: Re: [PATCH] x86: bug.h: merge annotate_reachable into _BUG_FLAGS for __WARN_FLAGS
To:     ndesaulniers@google.com
Cc:     adobriyan@gmail.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, jpoimboe@redhat.com, linux-kernel@vger.kernel.org,
        linux-sparse@vger.kernel.org, llvm@lists.linux.dev,
        luc.vanoostenryck@gmail.com, mingo@redhat.com, nathan@kernel.org,
        peterz@infradead.org, tglx@linutronix.de, x86@kernel.org,
        Sasha Levin <sashal@kernel.org>
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> @@ -75,9 +77,9 @@ do {                                \
>   */
>  #define __WARN_FLAGS(flags)                    \
>  do {                                \
> +    __auto_type f = BUGFLAG_WARNING|(flags);        \
>      instrumentation_begin();                \
> -    _BUG_FLAGS(ASM_UD2, BUGFLAG_WARNING|(flags));        \
> -    annotate_reachable();                    \
> +    _BUG_FLAGS(ASM_UD2, f, ASM_REACHABLE);            \
>      instrumentation_end();                    \
>  } while (0)

This causes following sparse warning on x86:

make allnoconfig && touch init/version.c && make CHECK="sparse
-Wshadow"  C=1 init/version.o
#
# No change to .config
#
 CALL    scripts/checksyscalls.sh
 CALL    scripts/atomic/check-atomics.sh
 CHK     include/generated/compile.h
 CC      init/version.o
 CHECK   init/version.c
init/version.c: note: in included file (through
include/linux/rculist.h, include/linux/pid.h, include/linux/sched.h,
include/linux/utsname.h):
./include/linux/rcupdate.h:1007:9: warning: symbol 'f' shadows an earlier one
./include/linux/rcupdate.h:1001:47: originally declared here


Affected versions (from the ones on kernel.org):

* 5.17 - bfb1a7c91fb7 ("x86/bug: Merge annotate_reachable() into
_BUG_FLAGS() asm")
* 5.16.17 - fe0c95903a68 ("x86/bug: Merge annotate_reachable() into
_BUG_FLAGS() asm")

Cannot be seen when changing the variable name:

diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index bab883c0b6fe..cbd11e38252a 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 __f = BUGFLAG_WARNING|(flags);        \
     instrumentation_begin();                \
-    _BUG_FLAGS(ASM_UD2, f, ASM_REACHABLE);            \
+    _BUG_FLAGS(ASM_UD2, __f, ASM_REACHABLE);            \
     instrumentation_end();                    \
 } while (0)