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Date:   Mon, 26 Apr 2021 09:30:21 -0700
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Subject: [PATCH v2] iw: set retain atrribute on sections
From:   Manoj Gupta <manojgupta@google.com>
To:     Johannes Berg <johannes.berg@intel.com>,
        Johannes Berg <johannes@sipsolutions.net>
Cc:     llozano@google.com, manojgupta@google.com,
        linux-wireless@vger.kernel.org, Fangrui Song <maskray@google.com>,
        stable@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

LLD 13 and GNU ld 2.37 support -z start-stop-gc which allows garbage
collection of C identifier name sections despite the __start_/__stop_
references.  Simply set the retain attribute so that GCC 11 (if
configure-time binutils is 2.36 or newer)/Clang 13 will set the
SHF_GNU_RETAIN section attribute to prevent garbage collection.

Without the patch, there are linker errors like the following with -z
start-stop-gc:
ld.lld: error: undefined symbol: __stop___cmd
>>> referenced by iw.c:418
>>>               iw.o:(__handle_cmd)

Suggested-by: Fangrui Song <maskray@google.com>

Cc: stable@vger.kernel.org

Signed-off-by: Manoj Gupta <manojgupta@google.com>
---
Changes v1 -> v2:
Apply the retain attribute to all places with attribute used.

 iw.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/iw.h b/iw.h
index 7f7f4fc..8ca8e44 100644
--- a/iw.h
+++ b/iw.h
@@ -118,8 +118,9 @@ struct chandef {
 		.parent = _section,					\
 		.selector = (_sel),					\
 	};								\
+	_Pragma("GCC diagnostic ignored \"-Wattributes\"") 		\
 	static struct cmd *__cmd ## _ ## _symname ## _ ## _handler ## _ ## _nlcmd ## _ ## _idby ## _ ## _hidden ## _p \
-	__attribute__((used,section("__cmd"))) =			\
+	__attribute__((used,retain,section("__cmd"))) =			\
 	&__cmd ## _ ## _symname ## _ ## _handler ## _ ## _nlcmd ## _ ## _idby ## _ ## _hidden
 #define __ACMD(_section, _symname, _name, _args, _nlcmd, _flags, _hidden, _idby, _handler, _help, _sel, _alias)\
 	__COMMAND(_section, _symname, _name, _args, _nlcmd, _flags, _hidden, _idby, _handler, _help, _sel);\
@@ -141,16 +142,18 @@ struct chandef {
 		.handler = (_handler),					\
 		.help = (_help),					\
 	 };								\
+	_Pragma("GCC diagnostic ignored \"-Wattributes\"") 		\
 	static struct cmd *__section ## _ ## _name ## _p		\
-	__attribute__((used,section("__cmd"))) = &__section ## _ ## _name
+	__attribute__((used,retain,section("__cmd"))) = &__section ## _ ## _name
 
 #define SECTION(_name)							\
 	struct cmd __section ## _ ## _name = {				\
 		.name = (#_name),					\
 		.hidden = 1,						\
 	};								\
+	_Pragma("GCC diagnostic ignored \"-Wattributes\"") 		\
 	static struct cmd *__section ## _ ## _name ## _p		\
-	__attribute__((used,section("__cmd"))) = &__section ## _ ## _name
+	__attribute__((used,retain,section("__cmd"))) = &__section ## _ ## _name
 
 #define DECLARE_SECTION(_name)						\
 	extern struct cmd __section ## _ ## _name;
@@ -162,13 +165,14 @@ struct vendor_event {
 };
 
 #define VENDOR_EVENT(_id, _subcmd, _callback)				\
+	_Pragma("GCC diagnostic ignored \"-Wattributes\"") 		\
 	const struct vendor_event 					\
 	vendor_event_ ## _id ## _ ## _subcmd = {			\
 		.vendor_id = _id,					\
 		.subcmd = _subcmd,					\
 		.callback = _callback,					\
 	}, * const vendor_event_ ## _id ## _ ## _subcmd ## _p		\
-	__attribute__((used,section("vendor_event"))) =			\
+	__attribute__((used,retain,section("vendor_event"))) =			\
 		&vendor_event_ ## _id ## _ ## _subcmd
 
 extern const char iw_version[];
-- 
2.31.1.498.g6c1eba8ee3d-goog