linux-kernel - [PATCH] slab: work around clang bug #42570

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Date:   Fri, 12 Jul 2019 11:04:39 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrey Konovalov <andreyknvl@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH] slab: work around clang bug #42570

Clang gets rather confused about two variables in the same special
section when one of them is not initialized, leading to an assembler
warning later:

/tmp/slab_common-18f869.s: Assembler messages:
/tmp/slab_common-18f869.s:7526: Warning: ignoring changed section attributes for .data..ro_after_init

Adding an initialization to kmalloc_caches is rather silly here
but does avoid the issue.

Link: https://bugs.llvm.org/show_bug.cgi?id=42570
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
We might decide to wait until this is fixed in clang, but
so far all versions targetting x86 seem to be affected.
---
 mm/slab_common.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 6c49dbb3769e..807490fe217a 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1028,7 +1028,8 @@ struct kmem_cache *__init create_kmalloc_cache(const char *name,
 }
 
 struct kmem_cache *
-kmalloc_caches[NR_KMALLOC_TYPES][KMALLOC_SHIFT_HIGH + 1] __ro_after_init;
+kmalloc_caches[NR_KMALLOC_TYPES][KMALLOC_SHIFT_HIGH + 1] __ro_after_init =
+{ /* initialization for https://bugs.llvm.org/show_bug.cgi?id=42570 */ };
 EXPORT_SYMBOL(kmalloc_caches);
 
 /*
-- 
2.20.0