[<prev] [next>] [day] [month] [year] [list]
Message-ID: <20250424194048.652571-1-marc.herbert@linux.intel.com>
Date: Thu, 24 Apr 2025 19:40:35 +0000
From: marc.herbert@...ux.intel.com
To: Marc.Herbert@...ux.intel.com
Cc: Kees Cook <kees@...nel.org>,
Miguel Ojeda <ojeda@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Marco Elver <elver@...gle.com>,
Changbin Du <changbin.du@...el.com>,
Tony Ambardar <tony.ambardar@...il.com>,
Jan Hendrik Farr <kernel@...rr.cc>,
Alexander Potapenko <glider@...gle.com>,
Uros Bizjak <ubizjak@...il.com>,
linux-kernel@...r.kernel.org
Subject: [PATCH] compiler_types.h: fix "unused variable" in __compiletime_assert()
From: Marc Herbert <Marc.Herbert@...ux.intel.com>
This refines commit c03567a8e8d5 ("include/linux/compiler.h: don't
perform compiletime_assert with -O0") and restores #ifdef __OPTIMIZE__
symmetry by evaluating the 'condition' variable in both compile-time
variants of __compiletimeassert().
As __OPTIMIZE__ is always true by default, this commit does not change
anything by default. But it fixes warnings with _non-default_ CFLAGS
like for instance this:
make CFLAGS_tcp.o='-Og -U__OPTIMIZE__'
from net/ipv4/tcp.c:273:
include/net/sch_generic.h: In function ‘qdisc_cb_private_validate’:
include/net/sch_generic.h:511:30:
error: unused variable ‘qcb’ [-Werror=unused-variable]
{
struct qdisc_skb_cb *qcb;
BUILD_BUG_ON(sizeof(skb->cb) < sizeof(*qcb));
...
}
Signed-off-by: Marc Herbert <Marc.Herbert@...ux.intel.com>
---
include/linux/compiler_types.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 501cffddc2f4..3f12ca49bb9e 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -525,6 +525,11 @@ struct ftrace_likely_data {
sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
#ifdef __OPTIMIZE__
+/* #ifdef __OPTIMIZE__ is only a good approximation; for instance "make
+ * CFLAGS_foo.o=-Og" defines __OPTIMIZE__, does not elide the
+ * conditional code and can break compilation with wrong error
+ * message(s). Combine with -U__OPTIMIZE__ when needed.
+ */
# define __compiletime_assert(condition, msg, prefix, suffix) \
do { \
/* \
@@ -538,7 +543,7 @@ struct ftrace_likely_data {
prefix ## suffix(); \
} while (0)
#else
-# define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
+# define __compiletime_assert(condition, msg, prefix, suffix) ((void)(condition))
#endif
#define _compiletime_assert(condition, msg, prefix, suffix) \
--
2.49.0
Powered by blists - more mailing lists