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From:   Sathvika Vasireddy <sv@linux.ibm.com>
To:     linuxppc-dev@lists.ozlabs.org
Cc:     jpoimboe@redhat.com, peterz@infradead.org,
        linux-kernel@vger.kernel.org, aik@ozlabs.ru, mpe@ellerman.id.au,
        mingo@redhat.com, christophe.leroy@csgroup.eu, rostedt@goodmis.org,
        mbenes@suse.cz, npiggin@gmail.com, chenzhongjin@huawei.com,
        naveen.n.rao@linux.vnet.ibm.com, sv@linux.ibm.com
Subject: [PATCH v3 01/16] powerpc: Fix __WARN_FLAGS() for use with Objtool
Date:   Mon, 12 Sep 2022 13:50:05 +0530
Message-Id: <20220912082020.226755-2-sv@linux.ibm.com>
In-Reply-To: <20220912082020.226755-1-sv@linux.ibm.com>
References: <20220912082020.226755-1-sv@linux.ibm.com>
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Commit 1e688dd2a3d675 ("powerpc/bug: Provide better flexibility to
WARN_ON/__WARN_FLAGS() with asm goto") updated __WARN_FLAGS() to use asm
goto, and added a call to 'unreachable()' after the asm goto for optimal
code generation. With CONFIG_OBJTOOL enabled, 'annotate_unreachable()'
statement in 'unreachable()' tries to note down the location of the
subsequent instruction in a separate elf section to aid code flow
analysis. However, on powerpc, this results in gcc emitting a call to a
symbol of size 0. This results in objtool complaining of "unannotated
intra-function call" since the target symbol is not a valid function
call destination.

Objtool wants this annotation for code flow analysis, which we are not
yet enabling on powerpc. As such, expand the call to 'unreachable()' in
__WARN_FLAGS() without annotate_unreachable():
        barrier_before_unreachable();
        __builtin_unreachable();

This still results in optimal code generation for __WARN_FLAGS(), while
getting rid of the objtool warning.

We still need barrier_before_unreachable() to work around gcc bugs 82365
and 106751:
- https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365
- https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106751

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
---
 arch/powerpc/include/asm/bug.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
index 61a4736355c2..ef42adb44aa3 100644
--- a/arch/powerpc/include/asm/bug.h
+++ b/arch/powerpc/include/asm/bug.h
@@ -99,7 +99,8 @@
 	__label__ __label_warn_on;				\
 								\
 	WARN_ENTRY("twi 31, 0, 0", BUGFLAG_WARNING | (flags), __label_warn_on); \
-	unreachable();						\
+	barrier_before_unreachable();				\
+	__builtin_unreachable();				\
 								\
 __label_warn_on:						\
 	break;							\
-- 
2.31.1